text: 
  /* pngrutil.c - utilities to read a PNG file
   *
   * Copyright (c) 2018 Cosmin Truta
   * Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson
   * Copyright (c) 1996-1997 Andreas Dilger
   * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
   *
   * This code is released under the libpng license.
   * For conditions of distribution and use, see the disclaimer
   * and license in png.h
   *
   * This file contains routines that are only called from within
   * libpng itself during the course of reading an image.
   */
  
  #include "pngpriv.h"
  
  #ifdef PNG_READ_SUPPORTED
  
  png_uint_32 PNGAPI
  png_get_uint_31(png_const_structrp png_ptr, png_const_bytep buf)
  {
     png_uint_32 uval = png_get_uint_32(buf);
  
     if (uval > PNG_UINT_31_MAX)
        png_error(png_ptr, "PNG unsigned integer out of range");
  
     return (uval);
  }
  
  #if defined(PNG_READ_gAMA_SUPPORTED) || defined(PNG_READ_cHRM_SUPPORTED)
  /* The following is a variation on the above for use with the fixed
   * point values used for gAMA and cHRM.  Instead of png_error it
   * issues a warning and returns (-1) - an invalid value because both
   * gAMA and cHRM use *unsigned* integers for fixed point values.
   */
  #define PNG_FIXED_ERROR (-1)
  
  static png_fixed_point /* PRIVATE */
  png_get_fixed_point(png_structrp png_ptr, png_const_bytep buf)
  {
     png_uint_32 uval = png_get_uint_32(buf);
  
     if (uval <= PNG_UINT_31_MAX)
        return (png_fixed_point)uval; /* known to be in range */
  
     /* The caller can turn off the warning by passing NULL. */
     if (png_ptr != NULL)
        png_warning(png_ptr, "PNG fixed point integer out of range");
  
     return PNG_FIXED_ERROR;
  }
  #endif
  
  #ifdef PNG_READ_INT_FUNCTIONS_SUPPORTED
  /* NOTE: the read macros will obscure these definitions, so that if
   * PNG_USE_READ_MACROS is set the library will not use them internally,
   * but the APIs will still be available externally.
   *
   * The parentheses around "PNGAPI function_name" in the following three
   * functions are necessary because they allow the macros to co-exist with
   * these (unused but exported) functions.
   */
  
  /* Grab an unsigned 32-bit integer from a buffer in big-endian format. */
  png_uint_32 (PNGAPI
  png_get_uint_32)(png_const_bytep buf)
  {
     png_uint_32 uval =
         ((png_uint_32)(*(buf    )) << 24) +
         ((png_uint_32)(*(buf + 1)) << 16) +
         ((png_uint_32)(*(buf + 2)) <<  8) +
         ((png_uint_32)(*(buf + 3))      ) ;
  
     return uval;
  }
  
  /* Grab a signed 32-bit integer from a buffer in big-endian format.  The
   * data is stored in the PNG file in two's complement format and there
   * is no guarantee that a 'png_int_32' is exactly 32 bits, therefore
   * the following code does a two's complement to native conversion.
   */
  png_int_32 (PNGAPI
  png_get_int_32)(png_const_bytep buf)
  {
     png_uint_32 uval = png_get_uint_32(buf);
     if ((uval & 0x80000000) == 0) /* non-negative */
        return (png_int_32)uval;
  
     uval = (uval ^ 0xffffffff) + 1;  /* 2's complement: -x = ~x+1 */
     if ((uval & 0x80000000) == 0) /* no overflow */
        return -(png_int_32)uval;
     /* The following has to be safe; this function only gets called on PNG data
      * and if we get here that data is invalid.  0 is the most safe value and
      * if not then an attacker would surely just generate a PNG with 0 instead.
      */
     return 0;
  }
  
  /* Grab an unsigned 16-bit integer from a buffer in big-endian format. */
  png_uint_16 (PNGAPI
  png_get_uint_16)(png_const_bytep buf)
  {
     /* ANSI-C requires an int value to accommodate at least 16 bits so this
      * works and allows the compiler not to worry about possible narrowing
      * on 32-bit systems.  (Pre-ANSI systems did not make integers smaller
      * than 16 bits either.)
      */
     unsigned int val =
         ((unsigned int)(*buf) << 8) +
         ((unsigned int)(*(buf + 1)));
  
     return (png_uint_16)val;
  }
  
  #endif /* READ_INT_FUNCTIONS */
  
  /* Read and check the PNG file signature */
  void /* PRIVATE */
  png_read_sig(png_structrp png_ptr, png_inforp info_ptr)
  {
     size_t num_checked, num_to_check;
  
     /* Exit if the user application does not expect a signature. */
     if (png_ptr->sig_bytes >= 8)
        return;
  
     num_checked = png_ptr->sig_bytes;
     num_to_check = 8 - num_checked;
  
  #ifdef PNG_IO_STATE_SUPPORTED
     png_ptr->io_state = PNG_IO_READING | PNG_IO_SIGNATURE;
  #endif
  
     /* The signature must be serialized in a single I/O call. */
     png_read_data(png_ptr, &(info_ptr->signature[num_checked]), num_to_check);
     png_ptr->sig_bytes = 8;
  
     if (png_sig_cmp(info_ptr->signature, num_checked, num_to_check) != 0)
     {
        if (num_checked < 4 &&
            png_sig_cmp(info_ptr->signature, num_checked, num_to_check - 4))
           png_error(png_ptr, "Not a PNG file");
        else
           png_error(png_ptr, "PNG file corrupted by ASCII conversion");
     }
     if (num_checked < 3)
        png_ptr->mode |= PNG_HAVE_PNG_SIGNATURE;
  }
  
  /* Read the chunk header (length + type name).
   * Put the type name into png_ptr->chunk_name, and return the length.
   */
  png_uint_32 /* PRIVATE */
  png_read_chunk_header(png_structrp png_ptr)
  {
     png_byte buf[8];
     png_uint_32 length;
  
  #ifdef PNG_IO_STATE_SUPPORTED
     png_ptr->io_state = PNG_IO_READING | PNG_IO_CHUNK_HDR;
  #endif
  
     /* Read the length and the chunk name.
      * This must be performed in a single I/O call.
      */
     png_read_data(png_ptr, buf, 8);
     length = png_get_uint_31(png_ptr, buf);
  
     /* Put the chunk name into png_ptr->chunk_name. */
     png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(buf+4);
  
     png_debug2(0, "Reading %lx chunk, length = %lu",
         (unsigned long)png_ptr->chunk_name, (unsigned long)length);
  
     /* Reset the crc and run it over the chunk name. */
     png_reset_crc(png_ptr);
     png_calculate_crc(png_ptr, buf + 4, 4);
  
     /* Check to see if chunk name is valid. */
     png_check_chunk_name(png_ptr, png_ptr->chunk_name);
  
     /* Check for too-large chunk length */
     png_check_chunk_length(png_ptr, length);
  
  #ifdef PNG_IO_STATE_SUPPORTED
     png_ptr->io_state = PNG_IO_READING | PNG_IO_CHUNK_DATA;
  #endif
  
     return length;
  }
  
  /* Read data, and (optionally) run it through the CRC. */
  void /* PRIVATE */
  png_crc_read(png_structrp png_ptr, png_bytep buf, png_uint_32 length)
  {
     if (png_ptr == NULL)
        return;
  
     png_read_data(png_ptr, buf, length);
     png_calculate_crc(png_ptr, buf, length);
  }
  
  /* Optionally skip data and then check the CRC.  Depending on whether we
   * are reading an ancillary or critical chunk, and how the program has set
   * things up, we may calculate the CRC on the data and print a message.
   * Returns '1' if there was a CRC error, '0' otherwise.
   */
  int /* PRIVATE */
  png_crc_finish(png_structrp png_ptr, png_uint_32 skip)
  {
     /* The size of the local buffer for inflate is a good guess as to a
      * reasonable size to use for buffering reads from the application.
      */
     while (skip > 0)
     {
        png_uint_32 len;
        png_byte tmpbuf[PNG_INFLATE_BUF_SIZE];
  
        len = (sizeof tmpbuf);
        if (len > skip)
           len = skip;
        skip -= len;
  
        png_crc_read(png_ptr, tmpbuf, len);
     }
  
     if (png_crc_error(png_ptr) != 0)
     {
        if (PNG_CHUNK_ANCILLARY(png_ptr->chunk_name) != 0 ?
            (png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN) == 0 :
            (png_ptr->flags & PNG_FLAG_CRC_CRITICAL_USE) != 0)
        {
           png_chunk_warning(png_ptr, "CRC error");
        }
  
        else
           png_chunk_error(png_ptr, "CRC error");
  
        return (1);
     }
  
     return (0);
  }
  
  /* Compare the CRC stored in the PNG file with that calculated by libpng from
   * the data it has read thus far.
   */
  int /* PRIVATE */
  png_crc_error(png_structrp png_ptr)
  {
     png_byte crc_bytes[4];
     png_uint_32 crc;
     int need_crc = 1;
  
     if (PNG_CHUNK_ANCILLARY(png_ptr->chunk_name) != 0)
     {
        if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_MASK) ==
            (PNG_FLAG_CRC_ANCILLARY_USE | PNG_FLAG_CRC_ANCILLARY_NOWARN))
           need_crc = 0;
     }
  
     else /* critical */
     {
        if ((png_ptr->flags & PNG_FLAG_CRC_CRITICAL_IGNORE) != 0)
           need_crc = 0;
     }
  
  #ifdef PNG_IO_STATE_SUPPORTED
     png_ptr->io_state = PNG_IO_READING | PNG_IO_CHUNK_CRC;
  #endif
  
     /* The chunk CRC must be serialized in a single I/O call. */
     png_read_data(png_ptr, crc_bytes, 4);
  
     if (need_crc != 0)
     {
        crc = png_get_uint_32(crc_bytes);
        return ((int)(crc != png_ptr->crc));
     }
  
     else
        return (0);
  }
  
  #if defined(PNG_READ_iCCP_SUPPORTED) || defined(PNG_READ_iTXt_SUPPORTED) ||\
      defined(PNG_READ_pCAL_SUPPORTED) || defined(PNG_READ_sCAL_SUPPORTED) ||\
      defined(PNG_READ_sPLT_SUPPORTED) || defined(PNG_READ_tEXt_SUPPORTED) ||\
      defined(PNG_READ_zTXt_SUPPORTED) || defined(PNG_SEQUENTIAL_READ_SUPPORTED)
  /* Manage the read buffer; this simply reallocates the buffer if it is not small
   * enough (or if it is not allocated).  The routine returns a pointer to the
   * buffer; if an error occurs and 'warn' is set the routine returns NULL, else
   * it will call png_error (via png_malloc) on failure.  (warn == 2 means
   * 'silent').
   */
  static png_bytep
  png_read_buffer(png_structrp png_ptr, png_alloc_size_t new_size, int warn)
  {
     png_bytep buffer = png_ptr->read_buffer;
  
     if (buffer != NULL && new_size > png_ptr->read_buffer_size)
     {
        png_ptr->read_buffer = NULL;
        png_ptr->read_buffer_size = 0;
        png_free(png_ptr, buffer);
        buffer = NULL;
     }
  
     if (buffer == NULL)
     {
        buffer = png_voidcast(png_bytep, png_malloc_base(png_ptr, new_size));
  
        if (buffer != NULL)
        {
           memset(buffer, 0, new_size); /* just in case */
           png_ptr->read_buffer = buffer;
           png_ptr->read_buffer_size = new_size;
        }
  
        else if (warn < 2) /* else silent */
        {
           if (warn != 0)
               png_chunk_warning(png_ptr, "insufficient memory to read chunk");
  
           else
               png_chunk_error(png_ptr, "insufficient memory to read chunk");
        }
     }
  
     return buffer;
  }
  #endif /* READ_iCCP|iTXt|pCAL|sCAL|sPLT|tEXt|zTXt|SEQUENTIAL_READ */
  
  /* png_inflate_claim: claim the zstream for some nefarious purpose that involves
   * decompression.  Returns Z_OK on success, else a zlib error code.  It checks
   * the owner but, in final release builds, just issues a warning if some other
   * chunk apparently owns the stream.  Prior to release it does a png_error.
   */
  static int
  png_inflate_claim(png_structrp png_ptr, png_uint_32 owner)
  {
     if (png_ptr->zowner != 0)
     {
        char msg[64];
  
        PNG_STRING_FROM_CHUNK(msg, png_ptr->zowner);
        /* So the message that results is "<chunk> using zstream"; this is an
         * internal error, but is very useful for debugging.  i18n requirements
         * are minimal.
         */
        (void)png_safecat(msg, (sizeof msg), 4, " using zstream");
  #if PNG_RELEASE_BUILD
        png_chunk_warning(png_ptr, msg);
        png_ptr->zowner = 0;
  #else
        png_chunk_error(png_ptr, msg);
  #endif
     }
  
     /* Implementation note: unlike 'png_deflate_claim' this internal function
      * does not take the size of the data as an argument.  Some efficiency could
      * be gained by using this when it is known *if* the zlib stream itself does
      * not record the number; however, this is an illusion: the original writer
      * of the PNG may have selected a lower window size, and we really must
      * follow that because, for systems with with limited capabilities, we
      * would otherwise reject the application's attempts to use a smaller window
      * size (zlib doesn't have an interface to say "this or lower"!).
      *
      * inflateReset2 was added to zlib 1.2.4; before this the window could not be
      * reset, therefore it is necessary to always allocate the maximum window
      * size with earlier zlibs just in case later compressed chunks need it.
      */
     {
        int ret; /* zlib return code */
  #if ZLIB_VERNUM >= 0x1240
        int window_bits = 0;
  
  # if defined(PNG_SET_OPTION_SUPPORTED) && defined(PNG_MAXIMUM_INFLATE_WINDOW)
        if (((png_ptr->options >> PNG_MAXIMUM_INFLATE_WINDOW) & 3) ==
            PNG_OPTION_ON)
        {
           window_bits = 15;
           png_ptr->zstream_start = 0; /* fixed window size */
        }
  
        else
        {
           png_ptr->zstream_start = 1;
        }
  # endif
  
  #endif /* ZLIB_VERNUM >= 0x1240 */
  
        /* Set this for safety, just in case the previous owner left pointers to
         * memory allocations.
         */
        png_ptr->zstream.next_in = NULL;
        png_ptr->zstream.avail_in = 0;
        png_ptr->zstream.next_out = NULL;
        png_ptr->zstream.avail_out = 0;
  
        if ((png_ptr->flags & PNG_FLAG_ZSTREAM_INITIALIZED) != 0)
        {
  #if ZLIB_VERNUM >= 0x1240
           ret = inflateReset2(&png_ptr->zstream, window_bits);
  #else
           ret = inflateReset(&png_ptr->zstream);
  #endif
        }
  
        else
        {
  #if ZLIB_VERNUM >= 0x1240
           ret = inflateInit2(&png_ptr->zstream, window_bits);
  #else
           ret = inflateInit(&png_ptr->zstream);
  #endif
  
           if (ret == Z_OK)
              png_ptr->flags |= PNG_FLAG_ZSTREAM_INITIALIZED;
        }
  
  #if ZLIB_VERNUM >= 0x1290 && \
     defined(PNG_SET_OPTION_SUPPORTED) && defined(PNG_IGNORE_ADLER32)
        if (((png_ptr->options >> PNG_IGNORE_ADLER32) & 3) == PNG_OPTION_ON)
           /* Turn off validation of the ADLER32 checksum in IDAT chunks */
           ret = inflateValidate(&png_ptr->zstream, 0);
  #endif
  
        if (ret == Z_OK)
           png_ptr->zowner = owner;
  
        else
           png_zstream_error(png_ptr, ret);
  
        return ret;
     }
  
  #ifdef window_bits
  # undef window_bits
  #endif
  }
  
  #if ZLIB_VERNUM >= 0x1240
  /* Handle the start of the inflate stream if we called inflateInit2(strm,0);
   * in this case some zlib versions skip validation of the CINFO field and, in
   * certain circumstances, libpng may end up displaying an invalid image, in
   * contrast to implementations that call zlib in the normal way (e.g. libpng
   * 1.5).
   */
  int /* PRIVATE */
  png_zlib_inflate(png_structrp png_ptr, int flush)
  {
     if (png_ptr->zstream_start && png_ptr->zstream.avail_in > 0)
     {
        if ((*png_ptr->zstream.next_in >> 4) > 7)
        {
           png_ptr->zstream.msg = "invalid window size (libpng)";
           return Z_DATA_ERROR;
        }
  
        png_ptr->zstream_start = 0;
     }
  
     return inflate(&png_ptr->zstream, flush);
  }
  #endif /* Zlib >= 1.2.4 */
  
  #ifdef PNG_READ_COMPRESSED_TEXT_SUPPORTED
  #if defined(PNG_READ_zTXt_SUPPORTED) || defined (PNG_READ_iTXt_SUPPORTED)
  /* png_inflate now returns zlib error codes including Z_OK and Z_STREAM_END to
   * allow the caller to do multiple calls if required.  If the 'finish' flag is
   * set Z_FINISH will be passed to the final inflate() call and Z_STREAM_END must
   * be returned or there has been a problem, otherwise Z_SYNC_FLUSH is used and
   * Z_OK or Z_STREAM_END will be returned on success.
   *
   * The input and output sizes are updated to the actual amounts of data consumed
   * or written, not the amount available (as in a z_stream).  The data pointers
   * are not changed, so the next input is (data+input_size) and the next
   * available output is (output+output_size).
   */
  static int
  png_inflate(png_structrp png_ptr, png_uint_32 owner, int finish,
      /* INPUT: */ png_const_bytep input, png_uint_32p input_size_ptr,
      /* OUTPUT: */ png_bytep output, png_alloc_size_t *output_size_ptr)
  {
     if (png_ptr->zowner == owner) /* Else not claimed */
     {
        int ret;
        png_alloc_size_t avail_out = *output_size_ptr;
        png_uint_32 avail_in = *input_size_ptr;
  
        /* zlib can't necessarily handle more than 65535 bytes at once (i.e. it
         * can't even necessarily handle 65536 bytes) because the type uInt is
         * "16 bits or more".  Consequently it is necessary to chunk the input to
         * zlib.  This code uses ZLIB_IO_MAX, from pngpriv.h, as the maximum (the
         * maximum value that can be stored in a uInt.)  It is possible to set
         * ZLIB_IO_MAX to a lower value in pngpriv.h and this may sometimes have
         * a performance advantage, because it reduces the amount of data accessed
         * at each step and that may give the OS more time to page it in.
         */
        png_ptr->zstream.next_in = PNGZ_INPUT_CAST(input);
        /* avail_in and avail_out are set below from 'size' */
        png_ptr->zstream.avail_in = 0;
        png_ptr->zstream.avail_out = 0;
  
        /* Read directly into the output if it is available (this is set to
         * a local buffer below if output is NULL).
         */
        if (output != NULL)
           png_ptr->zstream.next_out = output;
  
        do
        {
           uInt avail;
           Byte local_buffer[PNG_INFLATE_BUF_SIZE];
  
           /* zlib INPUT BUFFER */
           /* The setting of 'avail_in' used to be outside the loop; by setting it
            * inside it is possible to chunk the input to zlib and simply rely on
            * zlib to advance the 'next_in' pointer.  This allows arbitrary
            * amounts of data to be passed through zlib at the unavoidable cost of
            * requiring a window save (memcpy of up to 32768 output bytes)
            * every ZLIB_IO_MAX input bytes.
            */
           avail_in += png_ptr->zstream.avail_in; /* not consumed last time */
  
           avail = ZLIB_IO_MAX;
  
           if (avail_in < avail)
              avail = (uInt)avail_in; /* safe: < than ZLIB_IO_MAX */
  
           avail_in -= avail;
           png_ptr->zstream.avail_in = avail;
  
           /* zlib OUTPUT BUFFER */
           avail_out += png_ptr->zstream.avail_out; /* not written last time */
  
           avail = ZLIB_IO_MAX; /* maximum zlib can process */
  
           if (output == NULL)
           {
              /* Reset the output buffer each time round if output is NULL and
               * make available the full buffer, up to 'remaining_space'
               */
              png_ptr->zstream.next_out = local_buffer;
              if ((sizeof local_buffer) < avail)
                 avail = (sizeof local_buffer);
           }
  
           if (avail_out < avail)
              avail = (uInt)avail_out; /* safe: < ZLIB_IO_MAX */
  
           png_ptr->zstream.avail_out = avail;
           avail_out -= avail;
  
           /* zlib inflate call */
           /* In fact 'avail_out' may be 0 at this point, that happens at the end
            * of the read when the final LZ end code was not passed at the end of
            * the previous chunk of input data.  Tell zlib if we have reached the
            * end of the output buffer.
            */
           ret = PNG_INFLATE(png_ptr, avail_out > 0 ? Z_NO_FLUSH :
               (finish ? Z_FINISH : Z_SYNC_FLUSH));
        } while (ret == Z_OK);
  
        /* For safety kill the local buffer pointer now */
        if (output == NULL)
           png_ptr->zstream.next_out = NULL;
  
        /* Claw back the 'size' and 'remaining_space' byte counts. */
        avail_in += png_ptr->zstream.avail_in;
        avail_out += png_ptr->zstream.avail_out;
  
        /* Update the input and output sizes; the updated values are the amount
         * consumed or written, effectively the inverse of what zlib uses.
         */
        if (avail_out > 0)
           *output_size_ptr -= avail_out;
  
        if (avail_in > 0)
           *input_size_ptr -= avail_in;
  
        /* Ensure png_ptr->zstream.msg is set (even in the success case!) */
        png_zstream_error(png_ptr, ret);
        return ret;
     }
  
     else
     {
        /* This is a bad internal error.  The recovery assigns to the zstream msg
         * pointer, which is not owned by the caller, but this is safe; it's only
         * used on errors!
         */
        png_ptr->zstream.msg = PNGZ_MSG_CAST("zstream unclaimed");
        return Z_STREAM_ERROR;
     }
  }
  
  /*
   * Decompress trailing data in a chunk.  The assumption is that read_buffer
   * points at an allocated area holding the contents of a chunk with a
   * trailing compressed part.  What we get back is an allocated area
   * holding the original prefix part and an uncompressed version of the
   * trailing part (the malloc area passed in is freed).
   */
  static int
  png_decompress_chunk(png_structrp png_ptr,
      png_uint_32 chunklength, png_uint_32 prefix_size,
      png_alloc_size_t *newlength /* must be initialized to the maximum! */,
      int terminate /*add a '\0' to the end of the uncompressed data*/)
  {
     /* TODO: implement different limits for different types of chunk.
      *
      * The caller supplies *newlength set to the maximum length of the
      * uncompressed data, but this routine allocates space for the prefix and
      * maybe a '\0' terminator too.  We have to assume that 'prefix_size' is
      * limited only by the maximum chunk size.
      */
     png_alloc_size_t limit = PNG_SIZE_MAX;
  
  # ifdef PNG_SET_USER_LIMITS_SUPPORTED
     if (png_ptr->user_chunk_malloc_max > 0 &&
         png_ptr->user_chunk_malloc_max < limit)
        limit = png_ptr->user_chunk_malloc_max;
  # elif PNG_USER_CHUNK_MALLOC_MAX > 0
     if (PNG_USER_CHUNK_MALLOC_MAX < limit)
        limit = PNG_USER_CHUNK_MALLOC_MAX;
  # endif
  
     if (limit >= prefix_size + (terminate != 0))
     {
        int ret;
  
        limit -= prefix_size + (terminate != 0);
  
        if (limit < *newlength)
           *newlength = limit;
  
        /* Now try to claim the stream. */
        ret = png_inflate_claim(png_ptr, png_ptr->chunk_name);
  
        if (ret == Z_OK)
        {
           png_uint_32 lzsize = chunklength - prefix_size;
  
           ret = png_inflate(png_ptr, png_ptr->chunk_name, 1/*finish*/,
               /* input: */ png_ptr->read_buffer + prefix_size, &lzsize,
               /* output: */ NULL, newlength);
  
           if (ret == Z_STREAM_END)
           {
              /* Use 'inflateReset' here, not 'inflateReset2' because this
               * preserves the previously decided window size (otherwise it would
               * be necessary to store the previous window size.)  In practice
               * this doesn't matter anyway, because png_inflate will call inflate
               * with Z_FINISH in almost all cases, so the window will not be
               * maintained.
               */
              if (inflateReset(&png_ptr->zstream) == Z_OK)
              {
                 /* Because of the limit checks above we know that the new,
                  * expanded, size will fit in a size_t (let alone an
                  * png_alloc_size_t).  Use png_malloc_base here to avoid an
                  * extra OOM message.
                  */
                 png_alloc_size_t new_size = *newlength;
                 png_alloc_size_t buffer_size = prefix_size + new_size +
                     (terminate != 0);
                 png_bytep text = png_voidcast(png_bytep, png_malloc_base(png_ptr,
                     buffer_size));
  
                 if (text != NULL)
                 {
                    memset(text, 0, buffer_size);
  
                    ret = png_inflate(png_ptr, png_ptr->chunk_name, 1/*finish*/,
                        png_ptr->read_buffer + prefix_size, &lzsize,
                        text + prefix_size, newlength);
  
                    if (ret == Z_STREAM_END)
                    {
                       if (new_size == *newlength)
                       {
                          if (terminate != 0)
                             text[prefix_size + *newlength] = 0;
  
                          if (prefix_size > 0)
                             memcpy(text, png_ptr->read_buffer, prefix_size);
  
                          {
                             png_bytep old_ptr = png_ptr->read_buffer;
  
                             png_ptr->read_buffer = text;
                             png_ptr->read_buffer_size = buffer_size;
                             text = old_ptr; /* freed below */
                          }
                       }
  
                       else
                       {
                          /* The size changed on the second read, there can be no
                           * guarantee that anything is correct at this point.
                           * The 'msg' pointer has been set to "unexpected end of
                           * LZ stream", which is fine, but return an error code
                           * that the caller won't accept.
                           */
                          ret = PNG_UNEXPECTED_ZLIB_RETURN;
                       }
                    }
  
                    else if (ret == Z_OK)
                       ret = PNG_UNEXPECTED_ZLIB_RETURN; /* for safety */
  
                    /* Free the text pointer (this is the old read_buffer on
                     * success)
                     */
                    png_free(png_ptr, text);
  
                    /* This really is very benign, but it's still an error because
                     * the extra space may otherwise be used as a Trojan Horse.
                     */
                    if (ret == Z_STREAM_END &&
                        chunklength - prefix_size != lzsize)
                       png_chunk_benign_error(png_ptr, "extra compressed data");
                 }
  
                 else
                 {
                    /* Out of memory allocating the buffer */
                    ret = Z_MEM_ERROR;
                    png_zstream_error(png_ptr, Z_MEM_ERROR);
                 }
              }
  
              else
              {
                 /* inflateReset failed, store the error message */
                 png_zstream_error(png_ptr, ret);
                 ret = PNG_UNEXPECTED_ZLIB_RETURN;
              }
           }
  
           else if (ret == Z_OK)
              ret = PNG_UNEXPECTED_ZLIB_RETURN;
  
           /* Release the claimed stream */
           png_ptr->zowner = 0;
        }
  
        else /* the claim failed */ if (ret == Z_STREAM_END) /* impossible! */
           ret = PNG_UNEXPECTED_ZLIB_RETURN;
  
        return ret;
     }
  
     else
     {
        /* Application/configuration limits exceeded */
        png_zstream_error(png_ptr, Z_MEM_ERROR);
        return Z_MEM_ERROR;
     }
  }
  #endif /* READ_zTXt || READ_iTXt */
  #endif /* READ_COMPRESSED_TEXT */
  
  #ifdef PNG_READ_iCCP_SUPPORTED
  /* Perform a partial read and decompress, producing 'avail_out' bytes and
   * reading from the current chunk as required.
   */
  static int
  png_inflate_read(png_structrp png_ptr, png_bytep read_buffer, uInt read_size,
      png_uint_32p chunk_bytes, png_bytep next_out, png_alloc_size_t *out_size,
      int finish)
  {
     if (png_ptr->zowner == png_ptr->chunk_name)
     {
        int ret;
  
        /* next_in and avail_in must have been initialized by the caller. */
        png_ptr->zstream.next_out = next_out;
        png_ptr->zstream.avail_out = 0; /* set in the loop */
  
        do
        {
           if (png_ptr->zstream.avail_in == 0)
           {
              if (read_size > *chunk_bytes)
                 read_size = (uInt)*chunk_bytes;
              *chunk_bytes -= read_size;
  
              if (read_size > 0)
                 png_crc_read(png_ptr, read_buffer, read_size);
  
              png_ptr->zstream.next_in = read_buffer;
              png_ptr->zstream.avail_in = read_size;
           }
  
           if (png_ptr->zstream.avail_out == 0)
           {
              uInt avail = ZLIB_IO_MAX;
              if (avail > *out_size)
                 avail = (uInt)*out_size;
              *out_size -= avail;
  
              png_ptr->zstream.avail_out = avail;
           }
  
           /* Use Z_SYNC_FLUSH when there is no more chunk data to ensure that all
            * the available output is produced; this allows reading of truncated
            * streams.
            */
           ret = PNG_INFLATE(png_ptr, *chunk_bytes > 0 ?
               Z_NO_FLUSH : (finish ? Z_FINISH : Z_SYNC_FLUSH));
        }
        while (ret == Z_OK && (*out_size > 0 || png_ptr->zstream.avail_out > 0));
  
        *out_size += png_ptr->zstream.avail_out;
        png_ptr->zstream.avail_out = 0; /* Should not be required, but is safe */
  
        /* Ensure the error message pointer is always set: */
        png_zstream_error(png_ptr, ret);
        return ret;
     }
  
     else
     {
        png_ptr->zstream.msg = PNGZ_MSG_CAST("zstream unclaimed");
        return Z_STREAM_ERROR;
     }
  }
  #endif /* READ_iCCP */
  
  /* Read and check the IDHR chunk */
  
  void /* PRIVATE */
  png_handle_IHDR(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_byte buf[13];
     png_uint_32 width, height;
     int bit_depth, color_type, compression_type, filter_type;
     int interlace_type;
  
     png_debug(1, "in png_handle_IHDR");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) != 0)
        png_chunk_error(png_ptr, "out of place");
  
     /* Check the length */
     if (length != 13)
        png_chunk_error(png_ptr, "invalid");
  
     png_ptr->mode |= PNG_HAVE_IHDR;
  
     png_crc_read(png_ptr, buf, 13);
     png_crc_finish(png_ptr, 0);
  
     width = png_get_uint_31(png_ptr, buf);
     height = png_get_uint_31(png_ptr, buf + 4);
     bit_depth = buf[8];
     color_type = buf[9];
     compression_type = buf[10];
     filter_type = buf[11];
     interlace_type = buf[12];
  
  #ifdef PNG_READ_APNG_SUPPORTED
     png_ptr->first_frame_width = width;
     png_ptr->first_frame_height = height;
  #endif
  
     /* Set internal variables */
     png_ptr->width = width;
     png_ptr->height = height;
     png_ptr->bit_depth = (png_byte)bit_depth;
     png_ptr->interlaced = (png_byte)interlace_type;
     png_ptr->color_type = (png_byte)color_type;
  #ifdef PNG_MNG_FEATURES_SUPPORTED
     png_ptr->filter_type = (png_byte)filter_type;
  #endif
     png_ptr->compression_type = (png_byte)compression_type;
  
     /* Find number of channels */
     switch (png_ptr->color_type)
     {
        default: /* invalid, png_set_IHDR calls png_error */
        case PNG_COLOR_TYPE_GRAY:
        case PNG_COLOR_TYPE_PALETTE:
           png_ptr->channels = 1;
           break;
  
        case PNG_COLOR_TYPE_RGB:
           png_ptr->channels = 3;
           break;
  
        case PNG_COLOR_TYPE_GRAY_ALPHA:
           png_ptr->channels = 2;
           break;
  
        case PNG_COLOR_TYPE_RGB_ALPHA:
           png_ptr->channels = 4;
           break;
     }
  
     /* Set up other useful info */
     png_ptr->pixel_depth = (png_byte)(png_ptr->bit_depth * png_ptr->channels);
     png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth, png_ptr->width);
     png_debug1(3, "bit_depth = %d", png_ptr->bit_depth);
     png_debug1(3, "channels = %d", png_ptr->channels);
     png_debug1(3, "rowbytes = %lu", (unsigned long)png_ptr->rowbytes);
     png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth,
         color_type, interlace_type, compression_type, filter_type);
  }
  
  /* Read and check the palette */
  void /* PRIVATE */
  png_handle_PLTE(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_color palette[PNG_MAX_PALETTE_LENGTH];
     int max_palette_length, num, i;
  #ifdef PNG_POINTER_INDEXING_SUPPORTED
     png_colorp pal_ptr;
  #endif
  
     png_debug(1, "in png_handle_PLTE");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     /* Moved to before the 'after IDAT' check below because otherwise duplicate
      * PLTE chunks are potentially ignored (the spec says there shall not be more
      * than one PLTE, the error is not treated as benign, so this check trumps
      * the requirement that PLTE appears before IDAT.)
      */
     else if ((png_ptr->mode & PNG_HAVE_PLTE) != 0)
        png_chunk_error(png_ptr, "duplicate");
  
     else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
     {
        /* This is benign because the non-benign error happened before, when an
         * IDAT was encountered in a color-mapped image with no PLTE.
         */
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     png_ptr->mode |= PNG_HAVE_PLTE;
  
     if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) == 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "ignored in grayscale PNG");
        return;
     }
  
  #ifndef PNG_READ_OPT_PLTE_SUPPORTED
     if (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
     {
        png_crc_finish(png_ptr, length);
        return;
     }
  #endif
  
     if (length > 3*PNG_MAX_PALETTE_LENGTH || length % 3)
     {
        png_crc_finish(png_ptr, length);
  
        if (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
           png_chunk_benign_error(png_ptr, "invalid");
  
        else
           png_chunk_error(png_ptr, "invalid");
  
        return;
     }
  
     /* The cast is safe because 'length' is less than 3*PNG_MAX_PALETTE_LENGTH */
     num = (int)length / 3;
  
     /* If the palette has 256 or fewer entries but is too large for the bit
      * depth, we don't issue an error, to preserve the behavior of previous
      * libpng versions. We silently truncate the unused extra palette entries
      * here.
      */
     if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        max_palette_length = (1 << png_ptr->bit_depth);
     else
        max_palette_length = PNG_MAX_PALETTE_LENGTH;
  
     if (num > max_palette_length)
        num = max_palette_length;
  
  #ifdef PNG_POINTER_INDEXING_SUPPORTED
     for (i = 0, pal_ptr = palette; i < num; i++, pal_ptr++)
     {
        png_byte buf[3];
  
        png_crc_read(png_ptr, buf, 3);
        pal_ptr->red = buf[0];
        pal_ptr->green = buf[1];
        pal_ptr->blue = buf[2];
     }
  #else
     for (i = 0; i < num; i++)
     {
        png_byte buf[3];
  
        png_crc_read(png_ptr, buf, 3);
        /* Don't depend upon png_color being any order */
        palette[i].red = buf[0];
        palette[i].green = buf[1];
        palette[i].blue = buf[2];
     }
  #endif
  
     /* If we actually need the PLTE chunk (ie for a paletted image), we do
      * whatever the normal CRC configuration tells us.  However, if we
      * have an RGB image, the PLTE can be considered ancillary, so
      * we will act as though it is.
      */
  #ifndef PNG_READ_OPT_PLTE_SUPPORTED
     if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
  #endif
     {
        png_crc_finish(png_ptr, (png_uint_32) (length - (unsigned int)num * 3));
     }
  
  #ifndef PNG_READ_OPT_PLTE_SUPPORTED
     else if (png_crc_error(png_ptr) != 0)  /* Only if we have a CRC error */
     {
        /* If we don't want to use the data from an ancillary chunk,
         * we have two options: an error abort, or a warning and we
         * ignore the data in this chunk (which should be OK, since
         * it's considered ancillary for a RGB or RGBA image).
         *
         * IMPLEMENTATION NOTE: this is only here because png_crc_finish uses the
         * chunk type to determine whether to check the ancillary or the critical
         * flags.
         */
        if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_USE) == 0)
        {
           if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN) != 0)
              return;
  
           else
              png_chunk_error(png_ptr, "CRC error");
        }
  
        /* Otherwise, we (optionally) emit a warning and use the chunk. */
        else if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN) == 0)
           png_chunk_warning(png_ptr, "CRC error");
     }
  #endif
  
     /* TODO: png_set_PLTE has the side effect of setting png_ptr->palette to its
      * own copy of the palette.  This has the side effect that when png_start_row
      * is called (this happens after any call to png_read_update_info) the
      * info_ptr palette gets changed.  This is extremely unexpected and
      * confusing.
      *
      * Fix this by not sharing the palette in this way.
      */
     png_set_PLTE(png_ptr, info_ptr, palette, num);
  
     /* The three chunks, bKGD, hIST and tRNS *must* appear after PLTE and before
      * IDAT.  Prior to 1.6.0 this was not checked; instead the code merely
      * checked the apparent validity of a tRNS chunk inserted before PLTE on a
      * palette PNG.  1.6.0 attempts to rigorously follow the standard and
      * therefore does a benign error if the erroneous condition is detected *and*
      * cancels the tRNS if the benign error returns.  The alternative is to
      * amend the standard since it would be rather hypocritical of the standards
      * maintainers to ignore it.
      */
  #ifdef PNG_READ_tRNS_SUPPORTED
     if (png_ptr->num_trans > 0 ||
         (info_ptr != NULL && (info_ptr->valid & PNG_INFO_tRNS) != 0))
     {
        /* Cancel this because otherwise it would be used if the transforms
         * require it.  Don't cancel the 'valid' flag because this would prevent
         * detection of duplicate chunks.
         */
        png_ptr->num_trans = 0;
  
        if (info_ptr != NULL)
           info_ptr->num_trans = 0;
  
        png_chunk_benign_error(png_ptr, "tRNS must be after");
     }
  #endif
  
  #ifdef PNG_READ_hIST_SUPPORTED
     if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_hIST) != 0)
        png_chunk_benign_error(png_ptr, "hIST must be after");
  #endif
  
  #ifdef PNG_READ_bKGD_SUPPORTED
     if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_bKGD) != 0)
        png_chunk_benign_error(png_ptr, "bKGD must be after");
  #endif
  }
  
  void /* PRIVATE */
  png_handle_IEND(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_debug(1, "in png_handle_IEND");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0 ||
         (png_ptr->mode & PNG_HAVE_IDAT) == 0)
        png_chunk_error(png_ptr, "out of place");
  
     png_ptr->mode |= (PNG_AFTER_IDAT | PNG_HAVE_IEND);
  
     png_crc_finish(png_ptr, length);
  
     if (length != 0)
        png_chunk_benign_error(png_ptr, "invalid");
  
     PNG_UNUSED(info_ptr)
  }
  
  #ifdef PNG_READ_gAMA_SUPPORTED
  void /* PRIVATE */
  png_handle_gAMA(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_fixed_point igamma;
     png_byte buf[4];
  
     png_debug(1, "in png_handle_gAMA");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & (PNG_HAVE_IDAT|PNG_HAVE_PLTE)) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     if (length != 4)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     png_crc_read(png_ptr, buf, 4);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     igamma = png_get_fixed_point(NULL, buf);
  
     png_colorspace_set_gamma(png_ptr, &png_ptr->colorspace, igamma);
     png_colorspace_sync(png_ptr, info_ptr);
  }
  #endif
  
  #ifdef PNG_READ_sBIT_SUPPORTED
  void /* PRIVATE */
  png_handle_sBIT(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     unsigned int truelen, i;
     png_byte sample_depth;
     png_byte buf[4];
  
     png_debug(1, "in png_handle_sBIT");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & (PNG_HAVE_IDAT|PNG_HAVE_PLTE)) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_sBIT) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
     {
        truelen = 3;
        sample_depth = 8;
     }
  
     else
     {
        truelen = png_ptr->channels;
        sample_depth = png_ptr->bit_depth;
     }
  
     if (length != truelen || length > 4)
     {
        png_chunk_benign_error(png_ptr, "invalid");
        png_crc_finish(png_ptr, length);
        return;
     }
  
     buf[0] = buf[1] = buf[2] = buf[3] = sample_depth;
     png_crc_read(png_ptr, buf, truelen);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     for (i=0; i<truelen; ++i)
     {
        if (buf[i] == 0 || buf[i] > sample_depth)
        {
           png_chunk_benign_error(png_ptr, "invalid");
           return;
        }
     }
  
     if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) != 0)
     {
        png_ptr->sig_bit.red = buf[0];
        png_ptr->sig_bit.green = buf[1];
        png_ptr->sig_bit.blue = buf[2];
        png_ptr->sig_bit.alpha = buf[3];
     }
  
     else
     {
        png_ptr->sig_bit.gray = buf[0];
        png_ptr->sig_bit.red = buf[0];
        png_ptr->sig_bit.green = buf[0];
        png_ptr->sig_bit.blue = buf[0];
        png_ptr->sig_bit.alpha = buf[1];
     }
  
     png_set_sBIT(png_ptr, info_ptr, &(png_ptr->sig_bit));
  }
  #endif
  
  #ifdef PNG_READ_cHRM_SUPPORTED
  void /* PRIVATE */
  png_handle_cHRM(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_byte buf[32];
     png_xy xy;
  
     png_debug(1, "in png_handle_cHRM");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & (PNG_HAVE_IDAT|PNG_HAVE_PLTE)) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     if (length != 32)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     png_crc_read(png_ptr, buf, 32);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     xy.whitex = png_get_fixed_point(NULL, buf);
     xy.whitey = png_get_fixed_point(NULL, buf + 4);
     xy.redx   = png_get_fixed_point(NULL, buf + 8);
     xy.redy   = png_get_fixed_point(NULL, buf + 12);
     xy.greenx = png_get_fixed_point(NULL, buf + 16);
     xy.greeny = png_get_fixed_point(NULL, buf + 20);
     xy.bluex  = png_get_fixed_point(NULL, buf + 24);
     xy.bluey  = png_get_fixed_point(NULL, buf + 28);
  
     if (xy.whitex == PNG_FIXED_ERROR ||
         xy.whitey == PNG_FIXED_ERROR ||
         xy.redx   == PNG_FIXED_ERROR ||
         xy.redy   == PNG_FIXED_ERROR ||
         xy.greenx == PNG_FIXED_ERROR ||
         xy.greeny == PNG_FIXED_ERROR ||
         xy.bluex  == PNG_FIXED_ERROR ||
         xy.bluey  == PNG_FIXED_ERROR)
     {
        png_chunk_benign_error(png_ptr, "invalid values");
        return;
     }
  
     /* If a colorspace error has already been output skip this chunk */
     if ((png_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) != 0)
        return;
  
     if ((png_ptr->colorspace.flags & PNG_COLORSPACE_FROM_cHRM) != 0)
     {
        png_ptr->colorspace.flags |= PNG_COLORSPACE_INVALID;
        png_colorspace_sync(png_ptr, info_ptr);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     png_ptr->colorspace.flags |= PNG_COLORSPACE_FROM_cHRM;
     (void)png_colorspace_set_chromaticities(png_ptr, &png_ptr->colorspace, &xy,
         1/*prefer cHRM values*/);
     png_colorspace_sync(png_ptr, info_ptr);
  }
  #endif
  
  #ifdef PNG_READ_sRGB_SUPPORTED
  void /* PRIVATE */
  png_handle_sRGB(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_byte intent;
  
     png_debug(1, "in png_handle_sRGB");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & (PNG_HAVE_IDAT|PNG_HAVE_PLTE)) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     if (length != 1)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     png_crc_read(png_ptr, &intent, 1);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     /* If a colorspace error has already been output skip this chunk */
     if ((png_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) != 0)
        return;
  
     /* Only one sRGB or iCCP chunk is allowed, use the HAVE_INTENT flag to detect
      * this.
      */
     if ((png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_INTENT) != 0)
     {
        png_ptr->colorspace.flags |= PNG_COLORSPACE_INVALID;
        png_colorspace_sync(png_ptr, info_ptr);
        png_chunk_benign_error(png_ptr, "too many profiles");
        return;
     }
  
     (void)png_colorspace_set_sRGB(png_ptr, &png_ptr->colorspace, intent);
     png_colorspace_sync(png_ptr, info_ptr);
  }
  #endif /* READ_sRGB */
  
  #ifdef PNG_READ_iCCP_SUPPORTED
  void /* PRIVATE */
  png_handle_iCCP(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  /* Note: this does not properly handle profiles that are > 64K under DOS */
  {
     png_const_charp errmsg = NULL; /* error message output, or no error */
     int finished = 0; /* crc checked */
  
     png_debug(1, "in png_handle_iCCP");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & (PNG_HAVE_IDAT|PNG_HAVE_PLTE)) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     /* Consistent with all the above colorspace handling an obviously *invalid*
      * chunk is just ignored, so does not invalidate the color space.  An
      * alternative is to set the 'invalid' flags at the start of this routine
      * and only clear them in they were not set before and all the tests pass.
      */
  
     /* The keyword must be at least one character and there is a
      * terminator (0) byte and the compression method byte, and the
      * 'zlib' datastream is at least 11 bytes.
      */
     if (length < 14)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "too short");
        return;
     }
  
     /* If a colorspace error has already been output skip this chunk */
     if ((png_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) != 0)
     {
        png_crc_finish(png_ptr, length);
        return;
     }
  
     /* Only one sRGB or iCCP chunk is allowed, use the HAVE_INTENT flag to detect
      * this.
      */
     if ((png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_INTENT) == 0)
     {
        uInt read_length, keyword_length;
        char keyword[81];
  
        /* Find the keyword; the keyword plus separator and compression method
         * bytes can be at most 81 characters long.
         */
        read_length = 81; /* maximum */
        if (read_length > length)
           read_length = (uInt)length;
  
        png_crc_read(png_ptr, (png_bytep)keyword, read_length);
        length -= read_length;
  
        /* The minimum 'zlib' stream is assumed to be just the 2 byte header,
         * 5 bytes minimum 'deflate' stream, and the 4 byte checksum.
         */
        if (length < 11)
        {
           png_crc_finish(png_ptr, length);
           png_chunk_benign_error(png_ptr, "too short");
           return;
        }
  
        keyword_length = 0;
        while (keyword_length < 80 && keyword_length < read_length &&
           keyword[keyword_length] != 0)
           ++keyword_length;
  
        /* TODO: make the keyword checking common */
        if (keyword_length >= 1 && keyword_length <= 79)
        {
           /* We only understand '0' compression - deflate - so if we get a
            * different value we can't safely decode the chunk.
            */
           if (keyword_length+1 < read_length &&
              keyword[keyword_length+1] == PNG_COMPRESSION_TYPE_BASE)
           {
              read_length -= keyword_length+2;
  
              if (png_inflate_claim(png_ptr, png_iCCP) == Z_OK)
              {
                 Byte profile_header[132]={0};
                 Byte local_buffer[PNG_INFLATE_BUF_SIZE];
                 png_alloc_size_t size = (sizeof profile_header);
  
                 png_ptr->zstream.next_in = (Bytef*)keyword + (keyword_length+2);
                 png_ptr->zstream.avail_in = read_length;
                 (void)png_inflate_read(png_ptr, local_buffer,
                     (sizeof local_buffer), &length, profile_header, &size,
                     0/*finish: don't, because the output is too small*/);
  
                 if (size == 0)
                 {
                    /* We have the ICC profile header; do the basic header checks.
                     */
                    png_uint_32 profile_length = png_get_uint_32(profile_header);
  
                    if (png_icc_check_length(png_ptr, &png_ptr->colorspace,
                        keyword, profile_length) != 0)
                    {
                       /* The length is apparently ok, so we can check the 132
                        * byte header.
                        */
                       if (png_icc_check_header(png_ptr, &png_ptr->colorspace,
                           keyword, profile_length, profile_header,
                           png_ptr->color_type) != 0)
                       {
                          /* Now read the tag table; a variable size buffer is
                           * needed at this point, allocate one for the whole
                           * profile.  The header check has already validated
                           * that none of this stuff will overflow.
                           */
                          png_uint_32 tag_count =
                             png_get_uint_32(profile_header + 128);
                          png_bytep profile = png_read_buffer(png_ptr,
                              profile_length, 2/*silent*/);
  
                          if (profile != NULL)
                          {
                             memcpy(profile, profile_header,
                                 (sizeof profile_header));
  
                             size = 12 * tag_count;
  
                             (void)png_inflate_read(png_ptr, local_buffer,
                                 (sizeof local_buffer), &length,
                                 profile + (sizeof profile_header), &size, 0);
  
                             /* Still expect a buffer error because we expect
                              * there to be some tag data!
                              */
                             if (size == 0)
                             {
                                if (png_icc_check_tag_table(png_ptr,
                                    &png_ptr->colorspace, keyword, profile_length,
                                    profile) != 0)
                                {
                                   /* The profile has been validated for basic
                                    * security issues, so read the whole thing in.
                                    */
                                   size = profile_length - (sizeof profile_header)
                                       - 12 * tag_count;
  
                                   (void)png_inflate_read(png_ptr, local_buffer,
                                       (sizeof local_buffer), &length,
                                       profile + (sizeof profile_header) +
                                       12 * tag_count, &size, 1/*finish*/);
  
                                   if (length > 0 && !(png_ptr->flags &
                                       PNG_FLAG_BENIGN_ERRORS_WARN))
                                      errmsg = "extra compressed data";
  
                                   /* But otherwise allow extra data: */
                                   else if (size == 0)
                                   {
                                      if (length > 0)
                                      {
                                         /* This can be handled completely, so
                                          * keep going.
                                          */
                                         png_chunk_warning(png_ptr,
                                             "extra compressed data");
                                      }
  
                                      png_crc_finish(png_ptr, length);
                                      finished = 1;
  
  # if defined(PNG_sRGB_SUPPORTED) && PNG_sRGB_PROFILE_CHECKS >= 0
                                      /* Check for a match against sRGB */
                                      png_icc_set_sRGB(png_ptr,
                                          &png_ptr->colorspace, profile,
                                          png_ptr->zstream.adler);
  # endif
  
                                      /* Steal the profile for info_ptr. */
                                      if (info_ptr != NULL)
                                      {
                                         png_free_data(png_ptr, info_ptr,
                                             PNG_FREE_ICCP, 0);
  
                                         info_ptr->iccp_name = png_voidcast(char*,
                                             png_malloc_base(png_ptr,
                                             keyword_length+1));
                                         if (info_ptr->iccp_name != NULL)
                                         {
                                            memcpy(info_ptr->iccp_name, keyword,
                                                keyword_length+1);
                                            info_ptr->iccp_proflen =
                                                profile_length;
                                            info_ptr->iccp_profile = profile;
                                            png_ptr->read_buffer = NULL; /*steal*/
                                            info_ptr->free_me |= PNG_FREE_ICCP;
                                            info_ptr->valid |= PNG_INFO_iCCP;
                                         }
  
                                         else
                                         {
                                            png_ptr->colorspace.flags |=
                                               PNG_COLORSPACE_INVALID;
                                            errmsg = "out of memory";
                                         }
                                      }
  
                                      /* else the profile remains in the read
                                       * buffer which gets reused for subsequent
                                       * chunks.
                                       */
  
                                      if (info_ptr != NULL)
                                         png_colorspace_sync(png_ptr, info_ptr);
  
                                      if (errmsg == NULL)
                                      {
                                         png_ptr->zowner = 0;
                                         return;
                                      }
                                   }
                                   if (errmsg == NULL)
                                      errmsg = png_ptr->zstream.msg;
                                }
                                /* else png_icc_check_tag_table output an error */
                             }
                             else /* profile truncated */
                                errmsg = png_ptr->zstream.msg;
                          }
  
                          else
                             errmsg = "out of memory";
                       }
  
                       /* else png_icc_check_header output an error */
                    }
  
                    /* else png_icc_check_length output an error */
                 }
  
                 else /* profile truncated */
                    errmsg = png_ptr->zstream.msg;
  
                 /* Release the stream */
                 png_ptr->zowner = 0;
              }
  
              else /* png_inflate_claim failed */
                 errmsg = png_ptr->zstream.msg;
           }
  
           else
              errmsg = "bad compression method"; /* or missing */
        }
  
        else
           errmsg = "bad keyword";
     }
  
     else
        errmsg = "too many profiles";
  
     /* Failure: the reason is in 'errmsg' */
     if (finished == 0)
        png_crc_finish(png_ptr, length);
  
     png_ptr->colorspace.flags |= PNG_COLORSPACE_INVALID;
     png_colorspace_sync(png_ptr, info_ptr);
     if (errmsg != NULL) /* else already output */
        png_chunk_benign_error(png_ptr, errmsg);
  }
  #endif /* READ_iCCP */
  
  #ifdef PNG_READ_sPLT_SUPPORTED
  void /* PRIVATE */
  png_handle_sPLT(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  /* Note: this does not properly handle chunks that are > 64K under DOS */
  {
     png_bytep entry_start, buffer;
     png_sPLT_t new_palette;
     png_sPLT_entryp pp;
     png_uint_32 data_length;
     int entry_size, i;
     png_uint_32 skip = 0;
     png_uint_32 dl;
     size_t max_dl;
  
     png_debug(1, "in png_handle_sPLT");
  
  #ifdef PNG_USER_LIMITS_SUPPORTED
     if (png_ptr->user_chunk_cache_max != 0)
     {
        if (png_ptr->user_chunk_cache_max == 1)
        {
           png_crc_finish(png_ptr, length);
           return;
        }
  
        if (--png_ptr->user_chunk_cache_max == 1)
        {
           png_warning(png_ptr, "No space in chunk cache for sPLT");
           png_crc_finish(png_ptr, length);
           return;
        }
     }
  #endif
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
  #ifdef PNG_MAX_MALLOC_64K
     if (length > 65535U)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "too large to fit in memory");
        return;
     }
  #endif
  
     buffer = png_read_buffer(png_ptr, length+1, 2/*silent*/);
     if (buffer == NULL)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of memory");
        return;
     }
  
  
     /* WARNING: this may break if size_t is less than 32 bits; it is assumed
      * that the PNG_MAX_MALLOC_64K test is enabled in this case, but this is a
      * potential breakage point if the types in pngconf.h aren't exactly right.
      */
     png_crc_read(png_ptr, buffer, length);
  
     if (png_crc_finish(png_ptr, skip) != 0)
        return;
  
     buffer[length] = 0;
  
     for (entry_start = buffer; *entry_start; entry_start++)
        /* Empty loop to find end of name */ ;
  
     ++entry_start;
  
     /* A sample depth should follow the separator, and we should be on it  */
     if (length < 2U || entry_start > buffer + (length - 2U))
     {
        png_warning(png_ptr, "malformed sPLT chunk");
        return;
     }
  
     new_palette.depth = *entry_start++;
     entry_size = (new_palette.depth == 8 ? 6 : 10);
     /* This must fit in a png_uint_32 because it is derived from the original
      * chunk data length.
      */
     data_length = length - (png_uint_32)(entry_start - buffer);
  
     /* Integrity-check the data length */
     if ((data_length % (unsigned int)entry_size) != 0)
     {
        png_warning(png_ptr, "sPLT chunk has bad length");
        return;
     }
  
     dl = (png_uint_32)(data_length / (unsigned int)entry_size);
     max_dl = PNG_SIZE_MAX / (sizeof (png_sPLT_entry));
  
     if (dl > max_dl)
     {
        png_warning(png_ptr, "sPLT chunk too long");
        return;
     }
  
     new_palette.nentries = (png_int_32)(data_length / (unsigned int)entry_size);
  
     new_palette.entries = (png_sPLT_entryp)png_malloc_warn(png_ptr,
         (png_alloc_size_t) new_palette.nentries * (sizeof (png_sPLT_entry)));
  
     if (new_palette.entries == NULL)
     {
        png_warning(png_ptr, "sPLT chunk requires too much memory");
        return;
     }
  
  #ifdef PNG_POINTER_INDEXING_SUPPORTED
     for (i = 0; i < new_palette.nentries; i++)
     {
        pp = new_palette.entries + i;
  
        if (new_palette.depth == 8)
        {
           pp->red = *entry_start++;
           pp->green = *entry_start++;
           pp->blue = *entry_start++;
           pp->alpha = *entry_start++;
        }
  
        else
        {
           pp->red   = png_get_uint_16(entry_start); entry_start += 2;
           pp->green = png_get_uint_16(entry_start); entry_start += 2;
           pp->blue  = png_get_uint_16(entry_start); entry_start += 2;
           pp->alpha = png_get_uint_16(entry_start); entry_start += 2;
        }
  
        pp->frequency = png_get_uint_16(entry_start); entry_start += 2;
     }
  #else
     pp = new_palette.entries;
  
     for (i = 0; i < new_palette.nentries; i++)
     {
  
        if (new_palette.depth == 8)
        {
           pp[i].red   = *entry_start++;
           pp[i].green = *entry_start++;
           pp[i].blue  = *entry_start++;
           pp[i].alpha = *entry_start++;
        }
  
        else
        {
           pp[i].red   = png_get_uint_16(entry_start); entry_start += 2;
           pp[i].green = png_get_uint_16(entry_start); entry_start += 2;
           pp[i].blue  = png_get_uint_16(entry_start); entry_start += 2;
           pp[i].alpha = png_get_uint_16(entry_start); entry_start += 2;
        }
  
        pp[i].frequency = png_get_uint_16(entry_start); entry_start += 2;
     }
  #endif
  
     /* Discard all chunk data except the name and stash that */
     new_palette.name = (png_charp)buffer;
  
     png_set_sPLT(png_ptr, info_ptr, &new_palette, 1);
  
     png_free(png_ptr, new_palette.entries);
  }
  #endif /* READ_sPLT */
  
  #ifdef PNG_READ_tRNS_SUPPORTED
  void /* PRIVATE */
  png_handle_tRNS(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_byte readbuf[PNG_MAX_PALETTE_LENGTH];
  
     png_debug(1, "in png_handle_tRNS");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_tRNS) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     if (png_ptr->color_type == PNG_COLOR_TYPE_GRAY)
     {
        png_byte buf[2];
  
        if (length != 2)
        {
           png_crc_finish(png_ptr, length);
           png_chunk_benign_error(png_ptr, "invalid");
           return;
        }
  
        png_crc_read(png_ptr, buf, 2);
        png_ptr->num_trans = 1;
        png_ptr->trans_color.gray = png_get_uint_16(buf);
     }
  
     else if (png_ptr->color_type == PNG_COLOR_TYPE_RGB)
     {
        png_byte buf[6];
  
        if (length != 6)
        {
           png_crc_finish(png_ptr, length);
           png_chunk_benign_error(png_ptr, "invalid");
           return;
        }
  
        png_crc_read(png_ptr, buf, length);
        png_ptr->num_trans = 1;
        png_ptr->trans_color.red = png_get_uint_16(buf);
        png_ptr->trans_color.green = png_get_uint_16(buf + 2);
        png_ptr->trans_color.blue = png_get_uint_16(buf + 4);
     }
  
     else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
     {
        if ((png_ptr->mode & PNG_HAVE_PLTE) == 0)
        {
           /* TODO: is this actually an error in the ISO spec? */
           png_crc_finish(png_ptr, length);
           png_chunk_benign_error(png_ptr, "out of place");
           return;
        }
  
        if (length > (unsigned int) png_ptr->num_palette ||
           length > (unsigned int) PNG_MAX_PALETTE_LENGTH ||
           length == 0)
        {
           png_crc_finish(png_ptr, length);
           png_chunk_benign_error(png_ptr, "invalid");
           return;
        }
  
        png_crc_read(png_ptr, readbuf, length);
        png_ptr->num_trans = (png_uint_16)length;
     }
  
     else
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid with alpha channel");
        return;
     }
  
     if (png_crc_finish(png_ptr, 0) != 0)
     {
        png_ptr->num_trans = 0;
        return;
     }
  
     /* TODO: this is a horrible side effect in the palette case because the
      * png_struct ends up with a pointer to the tRNS buffer owned by the
      * png_info.  Fix this.
      */
     png_set_tRNS(png_ptr, info_ptr, readbuf, png_ptr->num_trans,
         &(png_ptr->trans_color));
  }
  #endif
  
  #ifdef PNG_READ_bKGD_SUPPORTED
  void /* PRIVATE */
  png_handle_bKGD(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     unsigned int truelen;
     png_byte buf[6];
     png_color_16 background;
  
     png_debug(1, "in png_handle_bKGD");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0 ||
         (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
         (png_ptr->mode & PNG_HAVE_PLTE) == 0))
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_bKGD) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        truelen = 1;
  
     else if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) != 0)
        truelen = 6;
  
     else
        truelen = 2;
  
     if (length != truelen)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     png_crc_read(png_ptr, buf, truelen);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     /* We convert the index value into RGB components so that we can allow
      * arbitrary RGB values for background when we have transparency, and
      * so it is easy to determine the RGB values of the background color
      * from the info_ptr struct.
      */
     if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
     {
        background.index = buf[0];
  
        if (info_ptr != NULL && info_ptr->num_palette != 0)
        {
           if (buf[0] >= info_ptr->num_palette)
           {
              png_chunk_benign_error(png_ptr, "invalid index");
              return;
           }
  
           background.red = (png_uint_16)png_ptr->palette[buf[0]].red;
           background.green = (png_uint_16)png_ptr->palette[buf[0]].green;
           background.blue = (png_uint_16)png_ptr->palette[buf[0]].blue;
        }
  
        else
           background.red = background.green = background.blue = 0;
  
        background.gray = 0;
     }
  
     else if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) == 0) /* GRAY */
     {
        if (png_ptr->bit_depth <= 8)
        {
           if (buf[0] != 0 || buf[1] >= (unsigned int)(1 << png_ptr->bit_depth))
           {
              png_chunk_benign_error(png_ptr, "invalid gray level");
              return;
           }
        }
  
        background.index = 0;
        background.red =
        background.green =
        background.blue =
        background.gray = png_get_uint_16(buf);
     }
  
     else
     {
        if (png_ptr->bit_depth <= 8)
        {
           if (buf[0] != 0 || buf[2] != 0 || buf[4] != 0)
           {
              png_chunk_benign_error(png_ptr, "invalid color");
              return;
           }
        }
  
        background.index = 0;
        background.red = png_get_uint_16(buf);
        background.green = png_get_uint_16(buf + 2);
        background.blue = png_get_uint_16(buf + 4);
        background.gray = 0;
     }
  
     png_set_bKGD(png_ptr, info_ptr, &background);
  }
  #endif
  
  #ifdef PNG_READ_eXIf_SUPPORTED
  void /* PRIVATE */
  png_handle_eXIf(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     unsigned int i;
  
     png_debug(1, "in png_handle_eXIf");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     if (length < 2)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "too short");
        return;
     }
  
     else if (info_ptr == NULL || (info_ptr->valid & PNG_INFO_eXIf) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     info_ptr->free_me |= PNG_FREE_EXIF;
  
     info_ptr->eXIf_buf = png_voidcast(png_bytep,
               png_malloc_warn(png_ptr, length));
  
     if (info_ptr->eXIf_buf == NULL)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of memory");
        return;
     }
  
     for (i = 0; i < length; i++)
     {
        png_byte buf[1];
        png_crc_read(png_ptr, buf, 1);
        info_ptr->eXIf_buf[i] = buf[0];
        if (i == 1 && buf[0] != 'M' && buf[0] != 'I'
                   && info_ptr->eXIf_buf[0] != buf[0])
        {
           png_crc_finish(png_ptr, length-i-1);
           png_chunk_benign_error(png_ptr, "incorrect byte-order specifier");
           png_free(png_ptr, info_ptr->eXIf_buf);
           info_ptr->eXIf_buf = NULL;
           return;
        }
     }
  
     if (png_crc_finish(png_ptr, 0) == 0)
        png_set_eXIf_1(png_ptr, info_ptr, length, info_ptr->eXIf_buf);
  
     png_free(png_ptr, info_ptr->eXIf_buf);
     info_ptr->eXIf_buf = NULL;
  }
  #endif
  
  #ifdef PNG_READ_hIST_SUPPORTED
  void /* PRIVATE */
  png_handle_hIST(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     unsigned int num, i;
     png_uint_16 readbuf[PNG_MAX_PALETTE_LENGTH];
  
     png_debug(1, "in png_handle_hIST");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0 ||
         (png_ptr->mode & PNG_HAVE_PLTE) == 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_hIST) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     num = length / 2 ;
  
     if (num != (unsigned int) png_ptr->num_palette ||
         num > (unsigned int) PNG_MAX_PALETTE_LENGTH)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     for (i = 0; i < num; i++)
     {
        png_byte buf[2];
  
        png_crc_read(png_ptr, buf, 2);
        readbuf[i] = png_get_uint_16(buf);
     }
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     png_set_hIST(png_ptr, info_ptr, readbuf);
  }
  #endif
  
  #ifdef PNG_READ_pHYs_SUPPORTED
  void /* PRIVATE */
  png_handle_pHYs(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_byte buf[9];
     png_uint_32 res_x, res_y;
     int unit_type;
  
     png_debug(1, "in png_handle_pHYs");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_pHYs) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     if (length != 9)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     png_crc_read(png_ptr, buf, 9);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     res_x = png_get_uint_32(buf);
     res_y = png_get_uint_32(buf + 4);
     unit_type = buf[8];
     png_set_pHYs(png_ptr, info_ptr, res_x, res_y, unit_type);
  }
  #endif
  
  #ifdef PNG_READ_oFFs_SUPPORTED
  void /* PRIVATE */
  png_handle_oFFs(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_byte buf[9];
     png_int_32 offset_x, offset_y;
     int unit_type;
  
     png_debug(1, "in png_handle_oFFs");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_oFFs) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     if (length != 9)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     png_crc_read(png_ptr, buf, 9);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     offset_x = png_get_int_32(buf);
     offset_y = png_get_int_32(buf + 4);
     unit_type = buf[8];
     png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y, unit_type);
  }
  #endif
  
  #ifdef PNG_READ_pCAL_SUPPORTED
  /* Read the pCAL chunk (described in the PNG Extensions document) */
  void /* PRIVATE */
  png_handle_pCAL(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_int_32 X0, X1;
     png_byte type, nparams;
     png_bytep buffer, buf, units, endptr;
     png_charpp params;
     int i;
  
     png_debug(1, "in png_handle_pCAL");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_pCAL) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     png_debug1(2, "Allocating and reading pCAL chunk data (%u bytes)",
         length + 1);
  
     buffer = png_read_buffer(png_ptr, length+1, 2/*silent*/);
  
     if (buffer == NULL)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of memory");
        return;
     }
  
     png_crc_read(png_ptr, buffer, length);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     buffer[length] = 0; /* Null terminate the last string */
  
     png_debug(3, "Finding end of pCAL purpose string");
     for (buf = buffer; *buf; buf++)
        /* Empty loop */ ;
  
     endptr = buffer + length;
  
     /* We need to have at least 12 bytes after the purpose string
      * in order to get the parameter information.
      */
     if (endptr - buf <= 12)
     {
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     png_debug(3, "Reading pCAL X0, X1, type, nparams, and units");
     X0 = png_get_int_32((png_bytep)buf+1);
     X1 = png_get_int_32((png_bytep)buf+5);
     type = buf[9];
     nparams = buf[10];
     units = buf + 11;
  
     png_debug(3, "Checking pCAL equation type and number of parameters");
     /* Check that we have the right number of parameters for known
      * equation types.
      */
     if ((type == PNG_EQUATION_LINEAR && nparams != 2) ||
         (type == PNG_EQUATION_BASE_E && nparams != 3) ||
         (type == PNG_EQUATION_ARBITRARY && nparams != 3) ||
         (type == PNG_EQUATION_HYPERBOLIC && nparams != 4))
     {
        png_chunk_benign_error(png_ptr, "invalid parameter count");
        return;
     }
  
     else if (type >= PNG_EQUATION_LAST)
     {
        png_chunk_benign_error(png_ptr, "unrecognized equation type");
     }
  
     for (buf = units; *buf; buf++)
        /* Empty loop to move past the units string. */ ;
  
     png_debug(3, "Allocating pCAL parameters array");
  
     params = png_voidcast(png_charpp, png_malloc_warn(png_ptr,
         nparams * (sizeof (png_charp))));
  
     if (params == NULL)
     {
        png_chunk_benign_error(png_ptr, "out of memory");
        return;
     }
  
     /* Get pointers to the start of each parameter string. */
     for (i = 0; i < nparams; i++)
     {
        buf++; /* Skip the null string terminator from previous parameter. */
  
        png_debug1(3, "Reading pCAL parameter %d", i);
  
        for (params[i] = (png_charp)buf; buf <= endptr && *buf != 0; buf++)
           /* Empty loop to move past each parameter string */ ;
  
        /* Make sure we haven't run out of data yet */
        if (buf > endptr)
        {
           png_free(png_ptr, params);
           png_chunk_benign_error(png_ptr, "invalid data");
           return;
        }
     }
  
     png_set_pCAL(png_ptr, info_ptr, (png_charp)buffer, X0, X1, type, nparams,
         (png_charp)units, params);
  
     png_free(png_ptr, params);
  }
  #endif
  
  #ifdef PNG_READ_sCAL_SUPPORTED
  /* Read the sCAL chunk */
  void /* PRIVATE */
  png_handle_sCAL(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_bytep buffer;
     size_t i;
     int state;
  
     png_debug(1, "in png_handle_sCAL");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of place");
        return;
     }
  
     else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_sCAL) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     /* Need unit type, width, \0, height: minimum 4 bytes */
     else if (length < 4)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     png_debug1(2, "Allocating and reading sCAL chunk data (%u bytes)",
         length + 1);
  
     buffer = png_read_buffer(png_ptr, length+1, 2/*silent*/);
  
     if (buffer == NULL)
     {
        png_chunk_benign_error(png_ptr, "out of memory");
        png_crc_finish(png_ptr, length);
        return;
     }
  
     png_crc_read(png_ptr, buffer, length);
     buffer[length] = 0; /* Null terminate the last string */
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     /* Validate the unit. */
     if (buffer[0] != 1 && buffer[0] != 2)
     {
        png_chunk_benign_error(png_ptr, "invalid unit");
        return;
     }
  
     /* Validate the ASCII numbers, need two ASCII numbers separated by
      * a '\0' and they need to fit exactly in the chunk data.
      */
     i = 1;
     state = 0;
  
     if (png_check_fp_number((png_const_charp)buffer, length, &state, &i) == 0 ||
         i >= length || buffer[i++] != 0)
        png_chunk_benign_error(png_ptr, "bad width format");
  
     else if (PNG_FP_IS_POSITIVE(state) == 0)
        png_chunk_benign_error(png_ptr, "non-positive width");
  
     else
     {
        size_t heighti = i;
  
        state = 0;
        if (png_check_fp_number((png_const_charp)buffer, length,
            &state, &i) == 0 || i != length)
           png_chunk_benign_error(png_ptr, "bad height format");
  
        else if (PNG_FP_IS_POSITIVE(state) == 0)
           png_chunk_benign_error(png_ptr, "non-positive height");
  
        else
           /* This is the (only) success case. */
           png_set_sCAL_s(png_ptr, info_ptr, buffer[0],
               (png_charp)buffer+1, (png_charp)buffer+heighti);
     }
  }
  #endif
  
  #ifdef PNG_READ_tIME_SUPPORTED
  void /* PRIVATE */
  png_handle_tIME(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_byte buf[7];
     png_time mod_time;
  
     png_debug(1, "in png_handle_tIME");
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_tIME) != 0)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "duplicate");
        return;
     }
  
     if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
        png_ptr->mode |= PNG_AFTER_IDAT;
  
     if (length != 7)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "invalid");
        return;
     }
  
     png_crc_read(png_ptr, buf, 7);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     mod_time.second = buf[6];
     mod_time.minute = buf[5];
     mod_time.hour = buf[4];
     mod_time.day = buf[3];
     mod_time.month = buf[2];
     mod_time.year = png_get_uint_16(buf);
  
     png_set_tIME(png_ptr, info_ptr, &mod_time);
  }
  #endif
  
  #ifdef PNG_READ_tEXt_SUPPORTED
  /* Note: this does not properly handle chunks that are > 64K under DOS */
  void /* PRIVATE */
  png_handle_tEXt(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_text  text_info;
     png_bytep buffer;
     png_charp key;
     png_charp text;
     png_uint_32 skip = 0;
  
     png_debug(1, "in png_handle_tEXt");
  
  #ifdef PNG_USER_LIMITS_SUPPORTED
     if (png_ptr->user_chunk_cache_max != 0)
     {
        if (png_ptr->user_chunk_cache_max == 1)
        {
           png_crc_finish(png_ptr, length);
           return;
        }
  
        if (--png_ptr->user_chunk_cache_max == 1)
        {
           png_crc_finish(png_ptr, length);
           png_chunk_benign_error(png_ptr, "no space in chunk cache");
           return;
        }
     }
  #endif
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
        png_ptr->mode |= PNG_AFTER_IDAT;
  
  #ifdef PNG_MAX_MALLOC_64K
     if (length > 65535U)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "too large to fit in memory");
        return;
     }
  #endif
  
     buffer = png_read_buffer(png_ptr, length+1, 1/*warn*/);
  
     if (buffer == NULL)
     {
        png_chunk_benign_error(png_ptr, "out of memory");
        return;
     }
  
     png_crc_read(png_ptr, buffer, length);
  
     if (png_crc_finish(png_ptr, skip) != 0)
        return;
  
     key = (png_charp)buffer;
     key[length] = 0;
  
     for (text = key; *text; text++)
        /* Empty loop to find end of key */ ;
  
     if (text != key + length)
        text++;
  
     text_info.compression = PNG_TEXT_COMPRESSION_NONE;
     text_info.key = key;
     text_info.lang = NULL;
     text_info.lang_key = NULL;
     text_info.itxt_length = 0;
     text_info.text = text;
     text_info.text_length = strlen(text);
  
     if (png_set_text_2(png_ptr, info_ptr, &text_info, 1) != 0)
        png_warning(png_ptr, "Insufficient memory to process text chunk");
  }
  #endif
  
  #ifdef PNG_READ_zTXt_SUPPORTED
  /* Note: this does not correctly handle chunks that are > 64K under DOS */
  void /* PRIVATE */
  png_handle_zTXt(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_const_charp errmsg = NULL;
     png_bytep       buffer;
     png_uint_32     keyword_length;
  
     png_debug(1, "in png_handle_zTXt");
  
  #ifdef PNG_USER_LIMITS_SUPPORTED
     if (png_ptr->user_chunk_cache_max != 0)
     {
        if (png_ptr->user_chunk_cache_max == 1)
        {
           png_crc_finish(png_ptr, length);
           return;
        }
  
        if (--png_ptr->user_chunk_cache_max == 1)
        {
           png_crc_finish(png_ptr, length);
           png_chunk_benign_error(png_ptr, "no space in chunk cache");
           return;
        }
     }
  #endif
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
        png_ptr->mode |= PNG_AFTER_IDAT;
  
     /* Note, "length" is sufficient here; we won't be adding
      * a null terminator later.
      */
     buffer = png_read_buffer(png_ptr, length, 2/*silent*/);
  
     if (buffer == NULL)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of memory");
        return;
     }
  
     png_crc_read(png_ptr, buffer, length);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     /* TODO: also check that the keyword contents match the spec! */
     for (keyword_length = 0;
        keyword_length < length && buffer[keyword_length] != 0;
        ++keyword_length)
        /* Empty loop to find end of name */ ;
  
     if (keyword_length > 79 || keyword_length < 1)
        errmsg = "bad keyword";
  
     /* zTXt must have some LZ data after the keyword, although it may expand to
      * zero bytes; we need a '\0' at the end of the keyword, the compression type
      * then the LZ data:
      */
     else if (keyword_length + 3 > length)
        errmsg = "truncated";
  
     else if (buffer[keyword_length+1] != PNG_COMPRESSION_TYPE_BASE)
        errmsg = "unknown compression type";
  
     else
     {
        png_alloc_size_t uncompressed_length = PNG_SIZE_MAX;
  
        /* TODO: at present png_decompress_chunk imposes a single application
         * level memory limit, this should be split to different values for iCCP
         * and text chunks.
         */
        if (png_decompress_chunk(png_ptr, length, keyword_length+2,
            &uncompressed_length, 1/*terminate*/) == Z_STREAM_END)
        {
           png_text text;
  
           if (png_ptr->read_buffer == NULL)
             errmsg="Read failure in png_handle_zTXt";
           else
           {
              /* It worked; png_ptr->read_buffer now looks like a tEXt chunk
               * except for the extra compression type byte and the fact that
               * it isn't necessarily '\0' terminated.
               */
              buffer = png_ptr->read_buffer;
              buffer[uncompressed_length+(keyword_length+2)] = 0;
  
              text.compression = PNG_TEXT_COMPRESSION_zTXt;
              text.key = (png_charp)buffer;
              text.text = (png_charp)(buffer + keyword_length+2);
              text.text_length = uncompressed_length;
              text.itxt_length = 0;
              text.lang = NULL;
              text.lang_key = NULL;
  
              if (png_set_text_2(png_ptr, info_ptr, &text, 1) != 0)
                 errmsg = "insufficient memory";
           }
        }
  
        else
           errmsg = png_ptr->zstream.msg;
     }
  
     if (errmsg != NULL)
        png_chunk_benign_error(png_ptr, errmsg);
  }
  #endif
  
  #ifdef PNG_READ_iTXt_SUPPORTED
  /* Note: this does not correctly handle chunks that are > 64K under DOS */
  void /* PRIVATE */
  png_handle_iTXt(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
  {
     png_const_charp errmsg = NULL;
     png_bytep buffer;
     png_uint_32 prefix_length;
  
     png_debug(1, "in png_handle_iTXt");
  
  #ifdef PNG_USER_LIMITS_SUPPORTED
     if (png_ptr->user_chunk_cache_max != 0)
     {
        if (png_ptr->user_chunk_cache_max == 1)
        {
           png_crc_finish(png_ptr, length);
           return;
        }
  
        if (--png_ptr->user_chunk_cache_max == 1)
        {
           png_crc_finish(png_ptr, length);
           png_chunk_benign_error(png_ptr, "no space in chunk cache");
           return;
        }
     }
  #endif
  
     if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
        png_chunk_error(png_ptr, "missing IHDR");
  
     if ((png_ptr->mode & PNG_HAVE_IDAT) != 0)
        png_ptr->mode |= PNG_AFTER_IDAT;
  
     buffer = png_read_buffer(png_ptr, length+1, 1/*warn*/);
  
     if (buffer == NULL)
     {
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "out of memory");
        return;
     }
  
     png_crc_read(png_ptr, buffer, length);
  
     if (png_crc_finish(png_ptr, 0) != 0)
        return;
  
     /* First the keyword. */
     for (prefix_length=0;
        prefix_length < length && buffer[prefix_length] != 0;
        ++prefix_length)
        /* Empty loop */ ;
  
     /* Perform a basic check on the keyword length here. */
     if (prefix_length > 79 || prefix_length < 1)
        errmsg = "bad keyword";
  
     /* Expect keyword, compression flag, compression type, language, translated
      * keyword (both may be empty but are 0 terminated) then the text, which may
      * be empty.
      */
     else if (prefix_length + 5 > length)
        errmsg = "truncated";
  
     else if (buffer[prefix_length+1] == 0 ||
        (buffer[prefix_length+1] == 1 &&
        buffer[prefix_length+2] == PNG_COMPRESSION_TYPE_BASE))
     {
        int compressed = buffer[prefix_length+1] != 0;
        png_uint_32 language_offset, translated_keyword_offset;
        png_alloc_size_t uncompressed_length = 0;
  
        /* Now the language tag */
        prefix_length += 3;
        language_offset = prefix_length;
  
        for (; prefix_length < length && buffer[prefix_length] != 0;
           ++prefix_length)
           /* Empty loop */ ;
  
        /* WARNING: the length may be invalid here, this is checked below. */
        translated_keyword_offset = ++prefix_length;
  
        for (; prefix_length < length && buffer[prefix_length] != 0;
           ++prefix_length)
           /* Empty loop */ ;
  
        /* prefix_length should now be at the trailing '\0' of the translated
         * keyword, but it may already be over the end.  None of this arithmetic
         * can overflow because chunks are at most 2^31 bytes long, but on 16-bit
         * systems the available allocation may overflow.
         */
        ++prefix_length;
  
        if (compressed == 0 && prefix_length <= length)
           uncompressed_length = length - prefix_length;
  
        else if (compressed != 0 && prefix_length < length)
        {
           uncompressed_length = PNG_SIZE_MAX;
  
           /* TODO: at present png_decompress_chunk imposes a single application
            * level memory limit, this should be split to different values for
            * iCCP and text chunks.
            */
           if (png_decompress_chunk(png_ptr, length, prefix_length,
               &uncompressed_length, 1/*terminate*/) == Z_STREAM_END)
              buffer = png_ptr->read_buffer;
  
           else
              errmsg = png_ptr->zstream.msg;
        }
  
        else
           errmsg = "truncated";
  
        if (errmsg == NULL)
        {
           png_text text;
  
           buffer[uncompressed_length+prefix_length] = 0;
  
           if (compressed == 0)
              text.compression = PNG_ITXT_COMPRESSION_NONE;
  
           else
              text.compression = PNG_ITXT_COMPRESSION_zTXt;
  
           text.key = (png_charp)buffer;
           text.lang = (png_charp)buffer + language_offset;
           text.lang_key = (png_charp)buffer + translated_keyword_offset;
           text.text = (png_charp)buffer + prefix_length;
           text.text_length = 0;
           text.itxt_length = uncompressed_length;
  
           if (png_set_text_2(png_ptr, info_ptr, &text, 1) != 0)
              errmsg = "insufficient memory";
        }
     }
  
     else
        errmsg = "bad compression info";
  
     if (errmsg != NULL)
        png_chunk_benign_error(png_ptr, errmsg);
  }
  #endif
  
  #ifdef PNG_READ_APNG_SUPPORTED
  void /* PRIVATE */
  png_handle_acTL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
  {
      png_byte data[8];
      png_uint_32 num_frames;
      png_uint_32 num_plays;
      png_uint_32 didSet;
  
      png_debug(1, "in png_handle_acTL");
  
      if (!(png_ptr->mode & PNG_HAVE_IHDR))
      {
          png_error(png_ptr, "Missing IHDR before acTL");
      }
      else if (png_ptr->mode & PNG_HAVE_IDAT)
      {
          png_warning(png_ptr, "Invalid acTL after IDAT skipped");
          png_crc_finish(png_ptr, length);
          return;
      }
      else if (png_ptr->mode & PNG_HAVE_acTL)
      {
          png_warning(png_ptr, "Duplicate acTL skipped");
          png_crc_finish(png_ptr, length);
          return;
      }
      else if (length != 8)
      {
          png_warning(png_ptr, "acTL with invalid length skipped");
          png_crc_finish(png_ptr, length);
          return;
      }
  
      png_crc_read(png_ptr, data, 8);
      png_crc_finish(png_ptr, 0);
  
      num_frames = png_get_uint_31(png_ptr, data);
      num_plays = png_get_uint_31(png_ptr, data + 4);
  
      /* the set function will do error checking on num_frames */
      didSet = png_set_acTL(png_ptr, info_ptr, num_frames, num_plays);
      if(didSet)
          png_ptr->mode |= PNG_HAVE_acTL;
  }
  
  void /* PRIVATE */
  png_handle_fcTL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
  {
      png_byte data[22];
      png_uint_32 width;
      png_uint_32 height;
      png_uint_32 x_offset;
      png_uint_32 y_offset;
      png_uint_16 delay_num;
      png_uint_16 delay_den;
      png_byte dispose_op;
      png_byte blend_op;
  
      png_debug(1, "in png_handle_fcTL");
  
      png_ensure_sequence_number(png_ptr, length);
  
      if (!(png_ptr->mode & PNG_HAVE_IHDR))
      {
          png_error(png_ptr, "Missing IHDR before fcTL");
      }
      else if (png_ptr->mode & PNG_HAVE_IDAT)
      {
          /* for any frames other then the first this message may be misleading,
          * but correct. PNG_HAVE_IDAT is unset before the frame head is read
          * i can't think of a better message */
          png_warning(png_ptr, "Invalid fcTL after IDAT skipped");
          png_crc_finish(png_ptr, length-4);
          return;
      }
      else if (png_ptr->mode & PNG_HAVE_fcTL)
      {
          png_warning(png_ptr, "Duplicate fcTL within one frame skipped");
          png_crc_finish(png_ptr, length-4);
          return;
      }
      else if (length != 26)
      {
          png_warning(png_ptr, "fcTL with invalid length skipped");
          png_crc_finish(png_ptr, length-4);
          return;
      }
  
      png_crc_read(png_ptr, data, 22);
      png_crc_finish(png_ptr, 0);
  
      width = png_get_uint_31(png_ptr, data);
      height = png_get_uint_31(png_ptr, data + 4);
      x_offset = png_get_uint_31(png_ptr, data + 8);
      y_offset = png_get_uint_31(png_ptr, data + 12);
      delay_num = png_get_uint_16(data + 16);
      delay_den = png_get_uint_16(data + 18);
      dispose_op = data[20];
      blend_op = data[21];
  
      if (png_ptr->num_frames_read == 0 && (x_offset != 0 || y_offset != 0))
      {
          png_warning(png_ptr, "fcTL for the first frame must have zero offset");
          return;
      }
  
      if (info_ptr != NULL)
      {
          if (png_ptr->num_frames_read == 0 &&
              (width != info_ptr->width || height != info_ptr->height))
          {
              png_warning(png_ptr, "size in first frame's fcTL must match "
                                 "the size in IHDR");
              return;
          }
  
          /* The set function will do more error checking */
          png_set_next_frame_fcTL(png_ptr, info_ptr, width, height,
                                  x_offset, y_offset, delay_num, delay_den,
                                  dispose_op, blend_op);
  
          png_read_reinit(png_ptr, info_ptr);
  
          png_ptr->mode |= PNG_HAVE_fcTL;
      }
  }
  
  void /* PRIVATE */
  png_have_info(png_structp png_ptr, png_infop info_ptr)
  {
      if((info_ptr->valid & PNG_INFO_acTL) && !(info_ptr->valid & PNG_INFO_fcTL))
      {
          png_ptr->apng_flags |= PNG_FIRST_FRAME_HIDDEN;
          info_ptr->num_frames++;
      }
  }
  
  void /* PRIVATE */
  png_handle_fdAT(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
  {
      png_ensure_sequence_number(png_ptr, length);
  
      /* This function is only called from png_read_end(), png_read_info(),
      * and png_push_read_chunk() which means that:
      * - the user doesn't want to read this frame
      * - or this is an out-of-place fdAT
      * in either case it is safe to ignore the chunk with a warning */
      png_warning(png_ptr, "ignoring fdAT chunk");
      png_crc_finish(png_ptr, length - 4);
      PNG_UNUSED(info_ptr)
  }
  
  void /* PRIVATE */
  png_ensure_sequence_number(png_structp png_ptr, png_uint_32 length)
  {
      png_byte data[4];
      png_uint_32 sequence_number;
  
      if (length < 4)
          png_error(png_ptr, "invalid fcTL or fdAT chunk found");
  
      png_crc_read(png_ptr, data, 4);
      sequence_number = png_get_uint_31(png_ptr, data);
  
      if (sequence_number != png_ptr->next_seq_num)
          png_error(png_ptr, "fcTL or fdAT chunk with out-of-order sequence "
                             "number found");
  
      png_ptr->next_seq_num++;
  }
  #endif /* PNG_READ_APNG_SUPPORTED */
  
  #ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
  /* Utility function for png_handle_unknown; set up png_ptr::unknown_chunk */
  static int
  png_cache_unknown_chunk(png_structrp png_ptr, png_uint_32 length)
  {
     png_alloc_size_t limit = PNG_SIZE_MAX;
  
     if (png_ptr->unknown_chunk.data != NULL)
     {
        png_free(png_ptr, png_ptr->unknown_chunk.data);
        png_ptr->unknown_chunk.data = NULL;
     }
  
  #  ifdef PNG_SET_USER_LIMITS_SUPPORTED
     if (png_ptr->user_chunk_malloc_max > 0 &&
         png_ptr->user_chunk_malloc_max < limit)
        limit = png_ptr->user_chunk_malloc_max;
  
  #  elif PNG_USER_CHUNK_MALLOC_MAX > 0
     if (PNG_USER_CHUNK_MALLOC_MAX < limit)
        limit = PNG_USER_CHUNK_MALLOC_MAX;
  #  endif
  
     if (length <= limit)
     {
        PNG_CSTRING_FROM_CHUNK(png_ptr->unknown_chunk.name, png_ptr->chunk_name);
        /* The following is safe because of the PNG_SIZE_MAX init above */
        png_ptr->unknown_chunk.size = (size_t)length/*SAFE*/;
        /* 'mode' is a flag array, only the bottom four bits matter here */
        png_ptr->unknown_chunk.location = (png_byte)png_ptr->mode/*SAFE*/;
  
        if (length == 0)
           png_ptr->unknown_chunk.data = NULL;
  
        else
        {
           /* Do a 'warn' here - it is handled below. */
           png_ptr->unknown_chunk.data = png_voidcast(png_bytep,
               png_malloc_warn(png_ptr, length));
        }
     }
  
     if (png_ptr->unknown_chunk.data == NULL && length > 0)
     {
        /* This is benign because we clean up correctly */
        png_crc_finish(png_ptr, length);
        png_chunk_benign_error(png_ptr, "unknown chunk exceeds memory limits");
        return 0;
     }
  
     else
     {
        if (length > 0)
           png_crc_read(png_ptr, png_ptr->unknown_chunk.data, length);
        png_crc_finish(png_ptr, 0);
        return 1;
     }
  }
  #endif /* READ_UNKNOWN_CHUNKS */
  
  /* Handle an unknown, or known but disabled, chunk */
  void /* PRIVATE */
  png_handle_unknown(png_structrp png_ptr, png_inforp info_ptr,
      png_uint_32 length, int keep)
  {
     int handled = 0; /* the chunk was handled */
  
     png_debug(1, "in png_handle_unknown");
  
  #ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
     /* NOTE: this code is based on the code in libpng-1.4.12 except for fixing
      * the bug which meant that setting a non-default behavior for a specific
      * chunk would be ignored (the default was always used unless a user
      * callback was installed).
      *
      * 'keep' is the value from the png_chunk_unknown_handling, the setting for
      * this specific chunk_name, if PNG_HANDLE_AS_UNKNOWN_SUPPORTED, if not it
      * will always be PNG_HANDLE_CHUNK_AS_DEFAULT and it needs to be set here.
      * This is just an optimization to avoid multiple calls to the lookup
      * function.
      */
  #  ifndef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
  #     ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
     keep = png_chunk_unknown_handling(png_ptr, png_ptr->chunk_name);
  #     endif
  #  endif
  
     /* One of the following methods will read the chunk or skip it (at least one
      * of these is always defined because this is the only way to switch on
      * PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
      */
  #  ifdef PNG_READ_USER_CHUNKS_SUPPORTED
     /* The user callback takes precedence over the chunk keep value, but the
      * keep value is still required to validate a save of a critical chunk.
      */
     if (png_ptr->read_user_chunk_fn != NULL)
     {
        if (png_cache_unknown_chunk(png_ptr, length) != 0)
        {
           /* Callback to user unknown chunk handler */
           int ret = (*(png_ptr->read_user_chunk_fn))(png_ptr,
               &png_ptr->unknown_chunk);
  
           /* ret is:
            * negative: An error occurred; png_chunk_error will be called.
            *     zero: The chunk was not handled, the chunk will be discarded
            *           unless png_set_keep_unknown_chunks has been used to set
            *           a 'keep' behavior for this particular chunk, in which
            *           case that will be used.  A critical chunk will cause an
            *           error at this point unless it is to be saved.
            * positive: The chunk was handled, libpng will ignore/discard it.
            */
           if (ret < 0)
              png_chunk_error(png_ptr, "error in user chunk");
  
           else if (ret == 0)
           {
              /* If the keep value is 'default' or 'never' override it, but
               * still error out on critical chunks unless the keep value is
               * 'always'  While this is weird it is the behavior in 1.4.12.
               * A possible improvement would be to obey the value set for the
               * chunk, but this would be an API change that would probably
               * damage some applications.
               *
               * The png_app_warning below catches the case that matters, where
               * the application has not set specific save or ignore for this
               * chunk or global save or ignore.
               */
              if (keep < PNG_HANDLE_CHUNK_IF_SAFE)
              {
  #              ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
                 if (png_ptr->unknown_default < PNG_HANDLE_CHUNK_IF_SAFE)
                 {
                    png_chunk_warning(png_ptr, "Saving unknown chunk:");
                    png_app_warning(png_ptr,
                        "forcing save of an unhandled chunk;"
                        " please call png_set_keep_unknown_chunks");
                        /* with keep = PNG_HANDLE_CHUNK_IF_SAFE */
                 }
  #              endif
                 keep = PNG_HANDLE_CHUNK_IF_SAFE;
              }
           }
  
           else /* chunk was handled */
           {
              handled = 1;
              /* Critical chunks can be safely discarded at this point. */
              keep = PNG_HANDLE_CHUNK_NEVER;
           }
        }
  
        else
           keep = PNG_HANDLE_CHUNK_NEVER; /* insufficient memory */
     }
  
     else
     /* Use the SAVE_UNKNOWN_CHUNKS code or skip the chunk */
  #  endif /* READ_USER_CHUNKS */
  
  #  ifdef PNG_SAVE_UNKNOWN_CHUNKS_SUPPORTED
     {
        /* keep is currently just the per-chunk setting, if there was no
         * setting change it to the global default now (not that this may
         * still be AS_DEFAULT) then obtain the cache of the chunk if required,
         * if not simply skip the chunk.
         */
        if (keep == PNG_HANDLE_CHUNK_AS_DEFAULT)
           keep = png_ptr->unknown_default;
  
        if (keep == PNG_HANDLE_CHUNK_ALWAYS ||
           (keep == PNG_HANDLE_CHUNK_IF_SAFE &&
            PNG_CHUNK_ANCILLARY(png_ptr->chunk_name)))
        {
           if (png_cache_unknown_chunk(png_ptr, length) == 0)
              keep = PNG_HANDLE_CHUNK_NEVER;
        }
  
        else
           png_crc_finish(png_ptr, length);
     }
  #  else
  #     ifndef PNG_READ_USER_CHUNKS_SUPPORTED
  #        error no method to support READ_UNKNOWN_CHUNKS
  #     endif
  
     {
        /* If here there is no read callback pointer set and no support is
         * compiled in to just save the unknown chunks, so simply skip this
         * chunk.  If 'keep' is something other than AS_DEFAULT or NEVER then
         * the app has erroneously asked for unknown chunk saving when there
         * is no support.
         */
        if (keep > PNG_HANDLE_CHUNK_NEVER)
           png_app_error(png_ptr, "no unknown chunk support available");
  
        png_crc_finish(png_ptr, length);
     }
  #  endif
  
  #  ifdef PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED
     /* Now store the chunk in the chunk list if appropriate, and if the limits
      * permit it.
      */
     if (keep == PNG_HANDLE_CHUNK_ALWAYS ||
        (keep == PNG_HANDLE_CHUNK_IF_SAFE &&
         PNG_CHUNK_ANCILLARY(png_ptr->chunk_name)))
     {
  #     ifdef PNG_USER_LIMITS_SUPPORTED
        switch (png_ptr->user_chunk_cache_max)
        {
           case 2:
              png_ptr->user_chunk_cache_max = 1;
              png_chunk_benign_error(png_ptr, "no space in chunk cache");
              /* FALLTHROUGH */
           case 1:
              /* NOTE: prior to 1.6.0 this case resulted in an unknown critical
               * chunk being skipped, now there will be a hard error below.
               */
              break;
  
           default: /* not at limit */
              --(png_ptr->user_chunk_cache_max);
              /* FALLTHROUGH */
           case 0: /* no limit */
  #  endif /* USER_LIMITS */
              /* Here when the limit isn't reached or when limits are compiled
               * out; store the chunk.
               */
              png_set_unknown_chunks(png_ptr, info_ptr,
                  &png_ptr->unknown_chunk, 1);
              handled = 1;
  #  ifdef PNG_USER_LIMITS_SUPPORTED
              break;
        }
  #  endif
     }
  #  else /* no store support: the chunk must be handled by the user callback */
     PNG_UNUSED(info_ptr)
  #  endif
  
     /* Regardless of the error handling below the cached data (if any) can be
      * freed now.  Notice that the data is not freed if there is a png_error, but
      * it will be freed by destroy_read_struct.
      */
     if (png_ptr->unknown_chunk.data != NULL)
        png_free(png_ptr, png_ptr->unknown_chunk.data);
     png_ptr->unknown_chunk.data = NULL;
  
  #else /* !PNG_READ_UNKNOWN_CHUNKS_SUPPORTED */
     /* There is no support to read an unknown chunk, so just skip it. */
     png_crc_finish(png_ptr, length);
     PNG_UNUSED(info_ptr)
     PNG_UNUSED(keep)
  #endif /* !READ_UNKNOWN_CHUNKS */
  
     /* Check for unhandled critical chunks */
     if (handled == 0 && PNG_CHUNK_CRITICAL(png_ptr->chunk_name))
        png_chunk_error(png_ptr, "unhandled critical chunk");
  }
  
  /* This function is called to verify that a chunk name is valid.
   * This function can't have the "critical chunk check" incorporated
   * into it, since in the future we will need to be able to call user
   * functions to handle unknown critical chunks after we check that
   * the chunk name itself is valid.
   */
  
  /* Bit hacking: the test for an invalid byte in the 4 byte chunk name is:
   *
   * ((c) < 65 || (c) > 122 || ((c) > 90 && (c) < 97))
   */
  
  void /* PRIVATE */
  png_check_chunk_name(png_const_structrp png_ptr, png_uint_32 chunk_name)
  {
     int i;
     png_uint_32 cn=chunk_name;
  
     png_debug(1, "in png_check_chunk_name");
  
     for (i=1; i<=4; ++i)
     {
        int c = cn & 0xff;
  
        if (c < 65 || c > 122 || (c > 90 && c < 97))
           png_chunk_error(png_ptr, "invalid chunk type");
  
        cn >>= 8;
     }
  }
  
  void /* PRIVATE */
  png_check_chunk_length(png_const_structrp png_ptr, png_uint_32 length)
  {
     png_alloc_size_t limit = PNG_UINT_31_MAX;
  
  # ifdef PNG_SET_USER_LIMITS_SUPPORTED
     if (png_ptr->user_chunk_malloc_max > 0 &&
         png_ptr->user_chunk_malloc_max < limit)
        limit = png_ptr->user_chunk_malloc_max;
  # elif PNG_USER_CHUNK_MALLOC_MAX > 0
     if (PNG_USER_CHUNK_MALLOC_MAX < limit)
        limit = PNG_USER_CHUNK_MALLOC_MAX;
  # endif
     if (png_ptr->chunk_name == png_IDAT)
     {
        png_alloc_size_t idat_limit = PNG_UINT_31_MAX;
        size_t row_factor =
           (size_t)png_ptr->width
           * (size_t)png_ptr->channels
           * (png_ptr->bit_depth > 8? 2: 1)
           + 1
           + (png_ptr->interlaced? 6: 0);
        if (png_ptr->height > PNG_UINT_32_MAX/row_factor)
           idat_limit = PNG_UINT_31_MAX;
        else
           idat_limit = png_ptr->height * row_factor;
        row_factor = row_factor > 32566? 32566 : row_factor;
        idat_limit += 6 + 5*(idat_limit/row_factor+1); /* zlib+deflate overhead */
        idat_limit=idat_limit < PNG_UINT_31_MAX? idat_limit : PNG_UINT_31_MAX;
        limit = limit < idat_limit? idat_limit : limit;
     }
  
     if (length > limit)
     {
        png_debug2(0," length = %lu, limit = %lu",
           (unsigned long)length,(unsigned long)limit);
        png_benign_error(png_ptr, "chunk data is too large");
     }
  }
  
  /* Combines the row recently read in with the existing pixels in the row.  This
   * routine takes care of alpha and transparency if requested.  This routine also
   * handles the two methods of progressive display of interlaced images,
   * depending on the 'display' value; if 'display' is true then the whole row
   * (dp) is filled from the start by replicating the available pixels.  If
   * 'display' is false only those pixels present in the pass are filled in.
   */
  void /* PRIVATE */
  png_combine_row(png_const_structrp png_ptr, png_bytep dp, int display)
  {
     unsigned int pixel_depth = png_ptr->transformed_pixel_depth;
     png_const_bytep sp = png_ptr->row_buf + 1;
     png_alloc_size_t row_width = png_ptr->width;
     unsigned int pass = png_ptr->pass;
     png_bytep end_ptr = 0;
     png_byte end_byte = 0;
     unsigned int end_mask;
  
     png_debug(1, "in png_combine_row");
  
     /* Added in 1.5.6: it should not be possible to enter this routine until at
      * least one row has been read from the PNG data and transformed.
      */
     if (pixel_depth == 0)
        png_error(png_ptr, "internal row logic error");
  
     /* Added in 1.5.4: the pixel depth should match the information returned by
      * any call to png_read_update_info at this point.  Do not continue if we got
      * this wrong.
      */
     if (png_ptr->info_rowbytes != 0 && png_ptr->info_rowbytes !=
            PNG_ROWBYTES(pixel_depth, row_width))
        png_error(png_ptr, "internal row size calculation error");
  
     /* Don't expect this to ever happen: */
     if (row_width == 0)
        png_error(png_ptr, "internal row width error");
  
     /* Preserve the last byte in cases where only part of it will be overwritten,
      * the multiply below may overflow, we don't care because ANSI-C guarantees
      * we get the low bits.
      */
     end_mask = (pixel_depth * row_width) & 7;
     if (end_mask != 0)
     {
        /* end_ptr == NULL is a flag to say do nothing */
        end_ptr = dp + PNG_ROWBYTES(pixel_depth, row_width) - 1;
        end_byte = *end_ptr;
  #     ifdef PNG_READ_PACKSWAP_SUPPORTED
        if ((png_ptr->transformations & PNG_PACKSWAP) != 0)
           /* little-endian byte */
           end_mask = (unsigned int)(0xff << end_mask);
  
        else /* big-endian byte */
  #     endif
        end_mask = 0xff >> end_mask;
        /* end_mask is now the bits to *keep* from the destination row */
     }
  
     /* For non-interlaced images this reduces to a memcpy(). A memcpy()
      * will also happen if interlacing isn't supported or if the application
      * does not call png_set_interlace_handling().  In the latter cases the
      * caller just gets a sequence of the unexpanded rows from each interlace
      * pass.
      */
  #ifdef PNG_READ_INTERLACING_SUPPORTED
     if (png_ptr->interlaced != 0 &&
         (png_ptr->transformations & PNG_INTERLACE) != 0 &&
         pass < 6 && (display == 0 ||
         /* The following copies everything for 'display' on passes 0, 2 and 4. */
         (display == 1 && (pass & 1) != 0)))
     {
        /* Narrow images may have no bits in a pass; the caller should handle
         * this, but this test is cheap:
         */
        if (row_width <= PNG_PASS_START_COL(pass))
           return;
  
        if (pixel_depth < 8)
        {
           /* For pixel depths up to 4 bpp the 8-pixel mask can be expanded to fit
            * into 32 bits, then a single loop over the bytes using the four byte
            * values in the 32-bit mask can be used.  For the 'display' option the
            * expanded mask may also not require any masking within a byte.  To
            * make this work the PACKSWAP option must be taken into account - it
            * simply requires the pixels to be reversed in each byte.
            *
            * The 'regular' case requires a mask for each of the first 6 passes,
            * the 'display' case does a copy for the even passes in the range
            * 0..6.  This has already been handled in the test above.
            *
            * The masks are arranged as four bytes with the first byte to use in
            * the lowest bits (little-endian) regardless of the order (PACKSWAP or
            * not) of the pixels in each byte.
            *
            * NOTE: the whole of this logic depends on the caller of this function
            * only calling it on rows appropriate to the pass.  This function only
            * understands the 'x' logic; the 'y' logic is handled by the caller.
            *
            * The following defines allow generation of compile time constant bit
            * masks for each pixel depth and each possibility of swapped or not
            * swapped bytes.  Pass 'p' is in the range 0..6; 'x', a pixel index,
            * is in the range 0..7; and the result is 1 if the pixel is to be
            * copied in the pass, 0 if not.  'S' is for the sparkle method, 'B'
            * for the block method.
            *
            * With some compilers a compile time expression of the general form:
            *
            *    (shift >= 32) ? (a >> (shift-32)) : (b >> shift)
            *
            * Produces warnings with values of 'shift' in the range 33 to 63
            * because the right hand side of the ?: expression is evaluated by
            * the compiler even though it isn't used.  Microsoft Visual C (various
            * versions) and the Intel C compiler are known to do this.  To avoid
            * this the following macros are used in 1.5.6.  This is a temporary
            * solution to avoid destabilizing the code during the release process.
            */
  #        if PNG_USE_COMPILE_TIME_MASKS
  #           define PNG_LSR(x,s) ((x)>>((s) & 0x1f))
  #           define PNG_LSL(x,s) ((x)<<((s) & 0x1f))
  #        else
  #           define PNG_LSR(x,s) ((x)>>(s))
  #           define PNG_LSL(x,s) ((x)<<(s))
  #        endif
  #        define S_COPY(p,x) (((p)<4 ? PNG_LSR(0x80088822,(3-(p))*8+(7-(x))) :\
             PNG_LSR(0xaa55ff00,(7-(p))*8+(7-(x)))) & 1)
  #        define B_COPY(p,x) (((p)<4 ? PNG_LSR(0xff0fff33,(3-(p))*8+(7-(x))) :\
             PNG_LSR(0xff55ff00,(7-(p))*8+(7-(x)))) & 1)
  
           /* Return a mask for pass 'p' pixel 'x' at depth 'd'.  The mask is
            * little endian - the first pixel is at bit 0 - however the extra
            * parameter 's' can be set to cause the mask position to be swapped
            * within each byte, to match the PNG format.  This is done by XOR of
            * the shift with 7, 6 or 4 for bit depths 1, 2 and 4.
            */
  #        define PIXEL_MASK(p,x,d,s) \
              (PNG_LSL(((PNG_LSL(1U,(d)))-1),(((x)*(d))^((s)?8-(d):0))))
  
           /* Hence generate the appropriate 'block' or 'sparkle' pixel copy mask.
            */
  #        define S_MASKx(p,x,d,s) (S_COPY(p,x)?PIXEL_MASK(p,x,d,s):0)
  #        define B_MASKx(p,x,d,s) (B_COPY(p,x)?PIXEL_MASK(p,x,d,s):0)
  
           /* Combine 8 of these to get the full mask.  For the 1-bpp and 2-bpp
            * cases the result needs replicating, for the 4-bpp case the above
            * generates a full 32 bits.
            */
  #        define MASK_EXPAND(m,d) ((m)*((d)==1?0x01010101:((d)==2?0x00010001:1)))
  
  #        define S_MASK(p,d,s) MASK_EXPAND(S_MASKx(p,0,d,s) + S_MASKx(p,1,d,s) +\
              S_MASKx(p,2,d,s) + S_MASKx(p,3,d,s) + S_MASKx(p,4,d,s) +\
              S_MASKx(p,5,d,s) + S_MASKx(p,6,d,s) + S_MASKx(p,7,d,s), d)
  
  #        define B_MASK(p,d,s) MASK_EXPAND(B_MASKx(p,0,d,s) + B_MASKx(p,1,d,s) +\
              B_MASKx(p,2,d,s) + B_MASKx(p,3,d,s) + B_MASKx(p,4,d,s) +\
              B_MASKx(p,5,d,s) + B_MASKx(p,6,d,s) + B_MASKx(p,7,d,s), d)
  
  #if PNG_USE_COMPILE_TIME_MASKS
           /* Utility macros to construct all the masks for a depth/swap
            * combination.  The 's' parameter says whether the format is PNG
            * (big endian bytes) or not.  Only the three odd-numbered passes are
            * required for the display/block algorithm.
            */
  #        define S_MASKS(d,s) { S_MASK(0,d,s), S_MASK(1,d,s), S_MASK(2,d,s),\
              S_MASK(3,d,s), S_MASK(4,d,s), S_MASK(5,d,s) }
  
  #        define B_MASKS(d,s) { B_MASK(1,d,s), B_MASK(3,d,s), B_MASK(5,d,s) }
  
  #        define DEPTH_INDEX(d) ((d)==1?0:((d)==2?1:2))
  
           /* Hence the pre-compiled masks indexed by PACKSWAP (or not), depth and
            * then pass:
            */
           static const png_uint_32 row_mask[2/*PACKSWAP*/][3/*depth*/][6] =
           {
              /* Little-endian byte masks for PACKSWAP */
              { S_MASKS(1,0), S_MASKS(2,0), S_MASKS(4,0) },
              /* Normal (big-endian byte) masks - PNG format */
              { S_MASKS(1,1), S_MASKS(2,1), S_MASKS(4,1) }
           };
  
           /* display_mask has only three entries for the odd passes, so index by
            * pass>>1.
            */
           static const png_uint_32 display_mask[2][3][3] =
           {
              /* Little-endian byte masks for PACKSWAP */
              { B_MASKS(1,0), B_MASKS(2,0), B_MASKS(4,0) },
              /* Normal (big-endian byte) masks - PNG format */
              { B_MASKS(1,1), B_MASKS(2,1), B_MASKS(4,1) }
           };
  
  #        define MASK(pass,depth,display,png)\
              ((display)?display_mask[png][DEPTH_INDEX(depth)][pass>>1]:\
                 row_mask[png][DEPTH_INDEX(depth)][pass])
  
  #else /* !PNG_USE_COMPILE_TIME_MASKS */
           /* This is the runtime alternative: it seems unlikely that this will
            * ever be either smaller or faster than the compile time approach.
            */
  #        define MASK(pass,depth,display,png)\
              ((display)?B_MASK(pass,depth,png):S_MASK(pass,depth,png))
  #endif /* !USE_COMPILE_TIME_MASKS */
  
           /* Use the appropriate mask to copy the required bits.  In some cases
            * the byte mask will be 0 or 0xff; optimize these cases.  row_width is
            * the number of pixels, but the code copies bytes, so it is necessary
            * to special case the end.
            */
           png_uint_32 pixels_per_byte = 8 / pixel_depth;
           png_uint_32 mask;
  
  #        ifdef PNG_READ_PACKSWAP_SUPPORTED
           if ((png_ptr->transformations & PNG_PACKSWAP) != 0)
              mask = MASK(pass, pixel_depth, display, 0);
  
           else
  #        endif
           mask = MASK(pass, pixel_depth, display, 1);
  
           for (;;)
           {
              png_uint_32 m;
  
              /* It doesn't matter in the following if png_uint_32 has more than
               * 32 bits because the high bits always match those in m<<24; it is,
               * however, essential to use OR here, not +, because of this.
               */
              m = mask;
              mask = (m >> 8) | (m << 24); /* rotate right to good compilers */
              m &= 0xff;
  
              if (m != 0) /* something to copy */
              {
                 if (m != 0xff)
                    *dp = (png_byte)((*dp & ~m) | (*sp & m));
                 else
                    *dp = *sp;
              }
  
              /* NOTE: this may overwrite the last byte with garbage if the image
               * is not an exact number of bytes wide; libpng has always done
               * this.
               */
              if (row_width <= pixels_per_byte)
                 break; /* May need to restore part of the last byte */
  
              row_width -= pixels_per_byte;
              ++dp;
              ++sp;
           }
        }
  
        else /* pixel_depth >= 8 */
        {
           unsigned int bytes_to_copy, bytes_to_jump;
  
           /* Validate the depth - it must be a multiple of 8 */
           if (pixel_depth & 7)
              png_error(png_ptr, "invalid user transform pixel depth");
  
           pixel_depth >>= 3; /* now in bytes */
           row_width *= pixel_depth;
  
           /* Regardless of pass number the Adam 7 interlace always results in a
            * fixed number of pixels to copy then to skip.  There may be a
            * different number of pixels to skip at the start though.
            */
           {
              unsigned int offset = PNG_PASS_START_COL(pass) * pixel_depth;
  
              row_width -= offset;
              dp += offset;
              sp += offset;
           }
  
           /* Work out the bytes to copy. */
           if (display != 0)
           {
              /* When doing the 'block' algorithm the pixel in the pass gets
               * replicated to adjacent pixels.  This is why the even (0,2,4,6)
               * passes are skipped above - the entire expanded row is copied.
               */
              bytes_to_copy = (1<<((6-pass)>>1)) * pixel_depth;
  
              /* But don't allow this number to exceed the actual row width. */
              if (bytes_to_copy > row_width)
                 bytes_to_copy = (unsigned int)/*SAFE*/row_width;
           }
  
           else /* normal row; Adam7 only ever gives us one pixel to copy. */
              bytes_to_copy = pixel_depth;
  
           /* In Adam7 there is a constant offset between where the pixels go. */
           bytes_to_jump = PNG_PASS_COL_OFFSET(pass) * pixel_depth;
  
           /* And simply copy these bytes.  Some optimization is possible here,
            * depending on the value of 'bytes_to_copy'.  Special case the low
            * byte counts, which we know to be frequent.
            *
            * Notice that these cases all 'return' rather than 'break' - this
            * avoids an unnecessary test on whether to restore the last byte
            * below.
            */
           switch (bytes_to_copy)
           {
              case 1:
                 for (;;)
                 {
                    *dp = *sp;
  
                    if (row_width <= bytes_to_jump)
                       return;
  
                    dp += bytes_to_jump;
                    sp += bytes_to_jump;
                    row_width -= bytes_to_jump;
                 }
  
              case 2:
                 /* There is a possibility of a partial copy at the end here; this
                  * slows the code down somewhat.
                  */
                 do
                 {
                    dp[0] = sp[0]; dp[1] = sp[1];
  
                    if (row_width <= bytes_to_jump)
                       return;
  
                    sp += bytes_to_jump;
                    dp += bytes_to_jump;
                    row_width -= bytes_to_jump;
                 }
                 while (row_width > 1);
  
                 /* And there can only be one byte left at this point: */
                 *dp = *sp;
                 return;
  
              case 3:
                 /* This can only be the RGB case, so each copy is exactly one
                  * pixel and it is not necessary to check for a partial copy.
                  */
                 for (;;)
                 {
                    dp[0] = sp[0]; dp[1] = sp[1]; dp[2] = sp[2];
  
                    if (row_width <= bytes_to_jump)
                       return;
  
                    sp += bytes_to_jump;
                    dp += bytes_to_jump;
                    row_width -= bytes_to_jump;
                 }
  
              default:
  #if PNG_ALIGN_TYPE != PNG_ALIGN_NONE
                 /* Check for double byte alignment and, if possible, use a
                  * 16-bit copy.  Don't attempt this for narrow images - ones that
                  * are less than an interlace panel wide.  Don't attempt it for
                  * wide bytes_to_copy either - use the memcpy there.
                  */
                 if (bytes_to_copy < 16 /*else use memcpy*/ &&
                     png_isaligned(dp, png_uint_16) &&
                     png_isaligned(sp, png_uint_16) &&
                     bytes_to_copy % (sizeof (png_uint_16)) == 0 &&
                     bytes_to_jump % (sizeof (png_uint_16)) == 0)
                 {
                    /* Everything is aligned for png_uint_16 copies, but try for
                     * png_uint_32 first.
                     */
                    if (png_isaligned(dp, png_uint_32) &&
                        png_isaligned(sp, png_uint_32) &&
                        bytes_to_copy % (sizeof (png_uint_32)) == 0 &&
                        bytes_to_jump % (sizeof (png_uint_32)) == 0)
                    {
                       png_uint_32p dp32 = png_aligncast(png_uint_32p,dp);
                       png_const_uint_32p sp32 = png_aligncastconst(
                           png_const_uint_32p, sp);
                       size_t skip = (bytes_to_jump-bytes_to_copy) /
                           (sizeof (png_uint_32));
  
                       do
                       {
                          size_t c = bytes_to_copy;
                          do
                          {
                             *dp32++ = *sp32++;
                             c -= (sizeof (png_uint_32));
                          }
                          while (c > 0);
  
                          if (row_width <= bytes_to_jump)
                             return;
  
                          dp32 += skip;
                          sp32 += skip;
                          row_width -= bytes_to_jump;
                       }
                       while (bytes_to_copy <= row_width);
  
                       /* Get to here when the row_width truncates the final copy.
                        * There will be 1-3 bytes left to copy, so don't try the
                        * 16-bit loop below.
                        */
                       dp = (png_bytep)dp32;
                       sp = (png_const_bytep)sp32;
                       do
                          *dp++ = *sp++;
                       while (--row_width > 0);
                       return;
                    }
  
                    /* Else do it in 16-bit quantities, but only if the size is
                     * not too large.
                     */
                    else
                    {
                       png_uint_16p dp16 = png_aligncast(png_uint_16p, dp);
                       png_const_uint_16p sp16 = png_aligncastconst(
                          png_const_uint_16p, sp);
                       size_t skip = (bytes_to_jump-bytes_to_copy) /
                          (sizeof (png_uint_16));
  
                       do
                       {
                          size_t c = bytes_to_copy;
                          do
                          {
                             *dp16++ = *sp16++;
                             c -= (sizeof (png_uint_16));
                          }
                          while (c > 0);
  
                          if (row_width <= bytes_to_jump)
                             return;
  
                          dp16 += skip;
                          sp16 += skip;
                          row_width -= bytes_to_jump;
                       }
                       while (bytes_to_copy <= row_width);
  
                       /* End of row - 1 byte left, bytes_to_copy > row_width: */
                       dp = (png_bytep)dp16;
                       sp = (png_const_bytep)sp16;
                       do
                          *dp++ = *sp++;
                       while (--row_width > 0);
                       return;
                    }
                 }
  #endif /* ALIGN_TYPE code */
  
                 /* The true default - use a memcpy: */
                 for (;;)
                 {
                    memcpy(dp, sp, bytes_to_copy);
  
                    if (row_width <= bytes_to_jump)
                       return;
  
                    sp += bytes_to_jump;
                    dp += bytes_to_jump;
                    row_width -= bytes_to_jump;
                    if (bytes_to_copy > row_width)
                       bytes_to_copy = (unsigned int)/*SAFE*/row_width;
                 }
           }
  
           /* NOT REACHED*/
        } /* pixel_depth >= 8 */
  
        /* Here if pixel_depth < 8 to check 'end_ptr' below. */
     }
     else
  #endif /* READ_INTERLACING */
  
     /* If here then the switch above wasn't used so just memcpy the whole row
      * from the temporary row buffer (notice that this overwrites the end of the
      * destination row if it is a partial byte.)
      */
     memcpy(dp, sp, PNG_ROWBYTES(pixel_depth, row_width));
  
     /* Restore the overwritten bits from the last byte if necessary. */
     if (end_ptr != NULL)
        *end_ptr = (png_byte)((end_byte & end_mask) | (*end_ptr & ~end_mask));
  }
  
  #ifdef PNG_READ_INTERLACING_SUPPORTED
  void /* PRIVATE */
  png_do_read_interlace(png_row_infop row_info, png_bytep row, int pass,
      png_uint_32 transformations /* Because these may affect the byte layout */)
  {
     /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
     /* Offset to next interlace block */
     static const unsigned int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
  
     png_debug(1, "in png_do_read_interlace");
     if (row != NULL && row_info != NULL)
     {
        png_uint_32 final_width;
  
        final_width = row_info->width * png_pass_inc[pass];
  
        switch (row_info->pixel_depth)
        {
           case 1:
           {
              png_bytep sp = row + (size_t)((row_info->width - 1) >> 3);
              png_bytep dp = row + (size_t)((final_width - 1) >> 3);
              unsigned int sshift, dshift;
              unsigned int s_start, s_end;
              int s_inc;
              int jstop = (int)png_pass_inc[pass];
              png_byte v;
              png_uint_32 i;
              int j;
  
  #ifdef PNG_READ_PACKSWAP_SUPPORTED
              if ((transformations & PNG_PACKSWAP) != 0)
              {
                  sshift = ((row_info->width + 7) & 0x07);
                  dshift = ((final_width + 7) & 0x07);
                  s_start = 7;
                  s_end = 0;
                  s_inc = -1;
              }
  
              else
  #endif
              {
                  sshift = 7 - ((row_info->width + 7) & 0x07);
                  dshift = 7 - ((final_width + 7) & 0x07);
                  s_start = 0;
                  s_end = 7;
                  s_inc = 1;
              }
  
              for (i = 0; i < row_info->width; i++)
              {
                 v = (png_byte)((*sp >> sshift) & 0x01);
                 for (j = 0; j < jstop; j++)
                 {
                    unsigned int tmp = *dp & (0x7f7f >> (7 - dshift));
                    tmp |= (unsigned int)(v << dshift);
                    *dp = (png_byte)(tmp & 0xff);
  
                    if (dshift == s_end)
                    {
                       dshift = s_start;
                       dp--;
                    }
  
                    else
                       dshift = (unsigned int)((int)dshift + s_inc);
                 }
  
                 if (sshift == s_end)
                 {
                    sshift = s_start;
                    sp--;
                 }
  
                 else
                    sshift = (unsigned int)((int)sshift + s_inc);
              }
              break;
           }
  
           case 2:
           {
              png_bytep sp = row + (png_uint_32)((row_info->width - 1) >> 2);
              png_bytep dp = row + (png_uint_32)((final_width - 1) >> 2);
              unsigned int sshift, dshift;
              unsigned int s_start, s_end;
              int s_inc;
              int jstop = (int)png_pass_inc[pass];
              png_uint_32 i;
  
  #ifdef PNG_READ_PACKSWAP_SUPPORTED
              if ((transformations & PNG_PACKSWAP) != 0)
              {
                 sshift = (((row_info->width + 3) & 0x03) << 1);
                 dshift = (((final_width + 3) & 0x03) << 1);
                 s_start = 6;
                 s_end = 0;
                 s_inc = -2;
              }
  
              else
  #endif
              {
                 sshift = ((3 - ((row_info->width + 3) & 0x03)) << 1);
                 dshift = ((3 - ((final_width + 3) & 0x03)) << 1);
                 s_start = 0;
                 s_end = 6;
                 s_inc = 2;
              }
  
              for (i = 0; i < row_info->width; i++)
              {
                 png_byte v;
                 int j;
  
                 v = (png_byte)((*sp >> sshift) & 0x03);
                 for (j = 0; j < jstop; j++)
                 {
                    unsigned int tmp = *dp & (0x3f3f >> (6 - dshift));
                    tmp |= (unsigned int)(v << dshift);
                    *dp = (png_byte)(tmp & 0xff);
  
                    if (dshift == s_end)
                    {
                       dshift = s_start;
                       dp--;
                    }
  
                    else
                       dshift = (unsigned int)((int)dshift + s_inc);
                 }
  
                 if (sshift == s_end)
                 {
                    sshift = s_start;
                    sp--;
                 }
  
                 else
                    sshift = (unsigned int)((int)sshift + s_inc);
              }
              break;
           }
  
           case 4:
           {
              png_bytep sp = row + (size_t)((row_info->width - 1) >> 1);
              png_bytep dp = row + (size_t)((final_width - 1) >> 1);
              unsigned int sshift, dshift;
              unsigned int s_start, s_end;
              int s_inc;
              png_uint_32 i;
              int jstop = (int)png_pass_inc[pass];
  
  #ifdef PNG_READ_PACKSWAP_SUPPORTED
              if ((transformations & PNG_PACKSWAP) != 0)
              {
                 sshift = (((row_info->width + 1) & 0x01) << 2);
                 dshift = (((final_width + 1) & 0x01) << 2);
                 s_start = 4;
                 s_end = 0;
                 s_inc = -4;
              }
  
              else
  #endif
              {
                 sshift = ((1 - ((row_info->width + 1) & 0x01)) << 2);
                 dshift = ((1 - ((final_width + 1) & 0x01)) << 2);
                 s_start = 0;
                 s_end = 4;
                 s_inc = 4;
              }
  
              for (i = 0; i < row_info->width; i++)
              {
                 png_byte v = (png_byte)((*sp >> sshift) & 0x0f);
                 int j;
  
                 for (j = 0; j < jstop; j++)
                 {
                    unsigned int tmp = *dp & (0xf0f >> (4 - dshift));
                    tmp |= (unsigned int)(v << dshift);
                    *dp = (png_byte)(tmp & 0xff);
  
                    if (dshift == s_end)
                    {
                       dshift = s_start;
                       dp--;
                    }
  
                    else
                       dshift = (unsigned int)((int)dshift + s_inc);
                 }
  
                 if (sshift == s_end)
                 {
                    sshift = s_start;
                    sp--;
                 }
  
                 else
                    sshift = (unsigned int)((int)sshift + s_inc);
              }
              break;
           }
  
           default:
           {
              size_t pixel_bytes = (row_info->pixel_depth >> 3);
  
              png_bytep sp = row + (size_t)(row_info->width - 1)
                  * pixel_bytes;
  
              png_bytep dp = row + (size_t)(final_width - 1) * pixel_bytes;
  
              int jstop = (int)png_pass_inc[pass];
              png_uint_32 i;
  
              for (i = 0; i < row_info->width; i++)
              {
                 png_byte v[8]; /* SAFE; pixel_depth does not exceed 64 */
                 int j;
  
                 memcpy(v, sp, pixel_bytes);
  
                 for (j = 0; j < jstop; j++)
                 {
                    memcpy(dp, v, pixel_bytes);
                    dp -= pixel_bytes;
                 }
  
                 sp -= pixel_bytes;
              }
              break;
           }
        }
  
        row_info->width = final_width;
        row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, final_width);
     }
  #ifndef PNG_READ_PACKSWAP_SUPPORTED
     PNG_UNUSED(transformations)  /* Silence compiler warning */
  #endif
  }
  #endif /* READ_INTERLACING */
  
  static void
  png_read_filter_row_sub(png_row_infop row_info, png_bytep row,
      png_const_bytep prev_row)
  {
     size_t i;
     size_t istop = row_info->rowbytes;
     unsigned int bpp = (row_info->pixel_depth + 7) >> 3;
     png_bytep rp = row + bpp;
  
     PNG_UNUSED(prev_row)
  
     for (i = bpp; i < istop; i++)
     {
        *rp = (png_byte)(((int)(*rp) + (int)(*(rp-bpp))) & 0xff);
        rp++;
     }
  }
  
  static void
  png_read_filter_row_up(png_row_infop row_info, png_bytep row,
      png_const_bytep prev_row)
  {
     size_t i;
     size_t istop = row_info->rowbytes;
     png_bytep rp = row;
     png_const_bytep pp = prev_row;
  
     for (i = 0; i < istop; i++)
     {
        *rp = (png_byte)(((int)(*rp) + (int)(*pp++)) & 0xff);
        rp++;
     }
  }
  
  static void
  png_read_filter_row_avg(png_row_infop row_info, png_bytep row,
      png_const_bytep prev_row)
  {
     size_t i;
     png_bytep rp = row;
     png_const_bytep pp = prev_row;
     unsigned int bpp = (row_info->pixel_depth + 7) >> 3;
     size_t istop = row_info->rowbytes - bpp;
  
     for (i = 0; i < bpp; i++)
     {
        *rp = (png_byte)(((int)(*rp) +
           ((int)(*pp++) / 2 )) & 0xff);
  
        rp++;
     }
  
     for (i = 0; i < istop; i++)
     {
        *rp = (png_byte)(((int)(*rp) +
           (int)(*pp++ + *(rp-bpp)) / 2 ) & 0xff);
  
        rp++;
     }
  }
  
  static void
  png_read_filter_row_paeth_1byte_pixel(png_row_infop row_info, png_bytep row,
      png_const_bytep prev_row)
  {
     png_bytep rp_end = row + row_info->rowbytes;
     int a, c;
  
     /* First pixel/byte */
     c = *prev_row++;
     a = *row + c;
     *row++ = (png_byte)a;
  
     /* Remainder */
     while (row < rp_end)
     {
        int b, pa, pb, pc, p;
  
        a &= 0xff; /* From previous iteration or start */
        b = *prev_row++;
  
        p = b - c;
        pc = a - c;
  
  #ifdef PNG_USE_ABS
        pa = abs(p);
        pb = abs(pc);
        pc = abs(p + pc);
  #else
        pa = p < 0 ? -p : p;
        pb = pc < 0 ? -pc : pc;
        pc = (p + pc) < 0 ? -(p + pc) : p + pc;
  #endif
  
        /* Find the best predictor, the least of pa, pb, pc favoring the earlier
         * ones in the case of a tie.
         */
        if (pb < pa)
        {
           pa = pb; a = b;
        }
        if (pc < pa) a = c;
  
        /* Calculate the current pixel in a, and move the previous row pixel to c
         * for the next time round the loop
         */
        c = b;
        a += *row;
        *row++ = (png_byte)a;
     }
  }
  
  static void
  png_read_filter_row_paeth_multibyte_pixel(png_row_infop row_info, png_bytep row,
      png_const_bytep prev_row)
  {
     unsigned int bpp = (row_info->pixel_depth + 7) >> 3;
     png_bytep rp_end = row + bpp;
  
     /* Process the first pixel in the row completely (this is the same as 'up'
      * because there is only one candidate predictor for the first row).
      */
     while (row < rp_end)
     {
        int a = *row + *prev_row++;
        *row++ = (png_byte)a;
     }
  
     /* Remainder */
     rp_end = rp_end + (row_info->rowbytes - bpp);
  
     while (row < rp_end)
     {
        int a, b, c, pa, pb, pc, p;
  
        c = *(prev_row - bpp);
        a = *(row - bpp);
        b = *prev_row++;
  
        p = b - c;
        pc = a - c;
  
  #ifdef PNG_USE_ABS
        pa = abs(p);
        pb = abs(pc);
        pc = abs(p + pc);
  #else
        pa = p < 0 ? -p : p;
        pb = pc < 0 ? -pc : pc;
        pc = (p + pc) < 0 ? -(p + pc) : p + pc;
  #endif
  
        if (pb < pa)
        {
           pa = pb; a = b;
        }
        if (pc < pa) a = c;
  
        a += *row;
        *row++ = (png_byte)a;
     }
  }
  
  static void
  png_init_filter_functions(png_structrp pp)
     /* This function is called once for every PNG image (except for PNG images
      * that only use PNG_FILTER_VALUE_NONE for all rows) to set the
      * implementations required to reverse the filtering of PNG rows.  Reversing
      * the filter is the first transformation performed on the row data.  It is
      * performed in place, therefore an implementation can be selected based on
      * the image pixel format.  If the implementation depends on image width then
      * take care to ensure that it works correctly if the image is interlaced -
      * interlacing causes the actual row width to vary.
      */
  {
     unsigned int bpp = (pp->pixel_depth + 7) >> 3;
  
     pp->read_filter[PNG_FILTER_VALUE_SUB-1] = png_read_filter_row_sub;
     pp->read_filter[PNG_FILTER_VALUE_UP-1] = png_read_filter_row_up;
     pp->read_filter[PNG_FILTER_VALUE_AVG-1] = png_read_filter_row_avg;
     if (bpp == 1)
        pp->read_filter[PNG_FILTER_VALUE_PAETH-1] =
           png_read_filter_row_paeth_1byte_pixel;
     else
        pp->read_filter[PNG_FILTER_VALUE_PAETH-1] =
           png_read_filter_row_paeth_multibyte_pixel;
  
  #ifdef PNG_FILTER_OPTIMIZATIONS
     /* To use this define PNG_FILTER_OPTIMIZATIONS as the name of a function to
      * call to install hardware optimizations for the above functions; simply
      * replace whatever elements of the pp->read_filter[] array with a hardware
      * specific (or, for that matter, generic) optimization.
      *
      * To see an example of this examine what configure.ac does when
      * --enable-arm-neon is specified on the command line.
      */
     PNG_FILTER_OPTIMIZATIONS(pp, bpp);
  #endif
  }
  
  void /* PRIVATE */
  png_read_filter_row(png_structrp pp, png_row_infop row_info, png_bytep row,
      png_const_bytep prev_row, int filter)
  {
     /* OPTIMIZATION: DO NOT MODIFY THIS FUNCTION, instead #define
      * PNG_FILTER_OPTIMIZATIONS to a function that overrides the generic
      * implementations.  See png_init_filter_functions above.
      */
     if (filter > PNG_FILTER_VALUE_NONE && filter < PNG_FILTER_VALUE_LAST)
     {
        if (pp->read_filter[0] == NULL)
           png_init_filter_functions(pp);
  
        pp->read_filter[filter-1](row_info, row, prev_row);
     }
  }
  
  #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
  void /* PRIVATE */
  png_read_IDAT_data(png_structrp png_ptr, png_bytep output,
      png_alloc_size_t avail_out)
  {
     /* Loop reading IDATs and decompressing the result into output[avail_out] */
     png_ptr->zstream.next_out = output;
     png_ptr->zstream.avail_out = 0; /* safety: set below */
  
     if (output == NULL)
        avail_out = 0;
  
     do
     {
        int ret;
        png_byte tmpbuf[PNG_INFLATE_BUF_SIZE];
  
        if (png_ptr->zstream.avail_in == 0)
        {
           uInt avail_in;
           png_bytep buffer;
  #ifdef PNG_READ_APNG_SUPPORTED
           png_uint_32 bytes_to_skip = 0;
  
           while (png_ptr->idat_size == 0 || bytes_to_skip != 0)
           {
              png_crc_finish(png_ptr, bytes_to_skip);
              bytes_to_skip = 0;
  
              png_ptr->idat_size = png_read_chunk_header(png_ptr);
              if (png_ptr->num_frames_read == 0)
              {
                 if (png_ptr->chunk_name != png_IDAT)
                    png_error(png_ptr, "Not enough image data");
              }
              else
              {
                 if (png_ptr->chunk_name == png_IEND)
                    png_error(png_ptr, "Not enough image data");
                 if (png_ptr->chunk_name != png_fdAT)
                 {
                    png_warning(png_ptr, "Skipped (ignored) a chunk "
                                         "between APNG chunks");
                    bytes_to_skip = png_ptr->idat_size;
                    continue;
                 }
  
                 png_ensure_sequence_number(png_ptr, png_ptr->idat_size);
  
                 png_ptr->idat_size -= 4;
              }
           }
  #else
           while (png_ptr->idat_size == 0)
           {
              png_crc_finish(png_ptr, 0);
  
              png_ptr->idat_size = png_read_chunk_header(png_ptr);
              /* This is an error even in the 'check' case because the code just
               * consumed a non-IDAT header.
               */
              if (png_ptr->chunk_name != png_IDAT)
                 png_error(png_ptr, "Not enough image data");
           }
  #endif /* PNG_READ_APNG_SUPPORTED */
           avail_in = png_ptr->IDAT_read_size;
  
           if (avail_in > png_ptr->idat_size)
              avail_in = (uInt)png_ptr->idat_size;
  
           /* A PNG with a gradually increasing IDAT size will defeat this attempt
            * to minimize memory usage by causing lots of re-allocs, but
            * realistically doing IDAT_read_size re-allocs is not likely to be a
            * big problem.
            */
           buffer = png_read_buffer(png_ptr, avail_in, 0/*error*/);
  
           png_crc_read(png_ptr, buffer, avail_in);
           png_ptr->idat_size -= avail_in;
  
           png_ptr->zstream.next_in = buffer;
           png_ptr->zstream.avail_in = avail_in;
        }
  
        /* And set up the output side. */
        if (output != NULL) /* standard read */
        {
           uInt out = ZLIB_IO_MAX;
  
           if (out > avail_out)
              out = (uInt)avail_out;
  
           avail_out -= out;
           png_ptr->zstream.avail_out = out;
        }
  
        else /* after last row, checking for end */
        {
           png_ptr->zstream.next_out = tmpbuf;
           png_ptr->zstream.avail_out = (sizeof tmpbuf);
        }
  
        /* Use NO_FLUSH; this gives zlib the maximum opportunity to optimize the
         * process.  If the LZ stream is truncated the sequential reader will
         * terminally damage the stream, above, by reading the chunk header of the
         * following chunk (it then exits with png_error).
         *
         * TODO: deal more elegantly with truncated IDAT lists.
         */
        ret = PNG_INFLATE(png_ptr, Z_NO_FLUSH);
  
        /* Take the unconsumed output back. */
        if (output != NULL)
           avail_out += png_ptr->zstream.avail_out;
  
        else /* avail_out counts the extra bytes */
           avail_out += (sizeof tmpbuf) - png_ptr->zstream.avail_out;
  
        png_ptr->zstream.avail_out = 0;
  
        if (ret == Z_STREAM_END)
        {
           /* Do this for safety; we won't read any more into this row. */
           png_ptr->zstream.next_out = NULL;
  
           png_ptr->mode |= PNG_AFTER_IDAT;
           png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
  #ifdef PNG_READ_APNG_SUPPORTED
           png_ptr->num_frames_read++;
  #endif
  
           if (png_ptr->zstream.avail_in > 0 || png_ptr->idat_size > 0)
              png_chunk_benign_error(png_ptr, "Extra compressed data");
           break;
        }
  
        if (ret != Z_OK)
        {
           png_zstream_error(png_ptr, ret);
  
           if (output != NULL)
              png_chunk_error(png_ptr, png_ptr->zstream.msg);
  
           else /* checking */
           {
              png_chunk_benign_error(png_ptr, png_ptr->zstream.msg);
              return;
           }
        }
     } while (avail_out > 0);
  
     if (avail_out > 0)
     {
        /* The stream ended before the image; this is the same as too few IDATs so
         * should be handled the same way.
         */
        if (output != NULL)
           png_error(png_ptr, "Not enough image data");
  
        else /* the deflate stream contained extra data */
           png_chunk_benign_error(png_ptr, "Too much image data");
     }
  }
  
  void /* PRIVATE */
  png_read_finish_IDAT(png_structrp png_ptr)
  {
     /* We don't need any more data and the stream should have ended, however the
      * LZ end code may actually not have been processed.  In this case we must
      * read it otherwise stray unread IDAT data or, more likely, an IDAT chunk
      * may still remain to be consumed.
      */
     if ((png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) == 0)
     {
        /* The NULL causes png_read_IDAT_data to swallow any remaining bytes in
         * the compressed stream, but the stream may be damaged too, so even after
         * this call we may need to terminate the zstream ownership.
         */
        png_read_IDAT_data(png_ptr, NULL, 0);
        png_ptr->zstream.next_out = NULL; /* safety */
  
        /* Now clear everything out for safety; the following may not have been
         * done.
         */
        if ((png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) == 0)
        {
           png_ptr->mode |= PNG_AFTER_IDAT;
           png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
        }
     }
  
     /* If the zstream has not been released do it now *and* terminate the reading
      * of the final IDAT chunk.
      */
     if (png_ptr->zowner == png_IDAT)
     {
        /* Always do this; the pointers otherwise point into the read buffer. */
        png_ptr->zstream.next_in = NULL;
        png_ptr->zstream.avail_in = 0;
  
        /* Now we no longer own the zstream. */
        png_ptr->zowner = 0;
  
        /* The slightly weird semantics of the sequential IDAT reading is that we
         * are always in or at the end of an IDAT chunk, so we always need to do a
         * crc_finish here.  If idat_size is non-zero we also need to read the
         * spurious bytes at the end of the chunk now.
         */
        (void)png_crc_finish(png_ptr, png_ptr->idat_size);
     }
  }
  
  void /* PRIVATE */
  png_read_finish_row(png_structrp png_ptr)
  {
     /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
  
     /* Start of interlace block */
     static const png_byte png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
  
     /* Offset to next interlace block */
     static const png_byte png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
  
     /* Start of interlace block in the y direction */
     static const png_byte png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
  
     /* Offset to next interlace block in the y direction */
     static const png_byte png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
  
     png_debug(1, "in png_read_finish_row");
     png_ptr->row_number++;
     if (png_ptr->row_number < png_ptr->num_rows)
        return;
  
     if (png_ptr->interlaced != 0)
     {
        png_ptr->row_number = 0;
  
        /* TO DO: don't do this if prev_row isn't needed (requires
         * read-ahead of the next row's filter byte.
         */
        memset(png_ptr->prev_row, 0, png_ptr->rowbytes + 1);
  
        do
        {
           png_ptr->pass++;
  
           if (png_ptr->pass >= 7)
              break;
  
           png_ptr->iwidth = (png_ptr->width +
              png_pass_inc[png_ptr->pass] - 1 -
              png_pass_start[png_ptr->pass]) /
              png_pass_inc[png_ptr->pass];
  
           if ((png_ptr->transformations & PNG_INTERLACE) == 0)
           {
              png_ptr->num_rows = (png_ptr->height +
                  png_pass_yinc[png_ptr->pass] - 1 -
                  png_pass_ystart[png_ptr->pass]) /
                  png_pass_yinc[png_ptr->pass];
           }
  
           else  /* if (png_ptr->transformations & PNG_INTERLACE) */
              break; /* libpng deinterlacing sees every row */
  
        } while (png_ptr->num_rows == 0 || png_ptr->iwidth == 0);
  
        if (png_ptr->pass < 7)
           return;
     }
  
     /* Here after at the end of the last row of the last pass. */
     png_read_finish_IDAT(png_ptr);
  }
  #endif /* SEQUENTIAL_READ */
  
  void /* PRIVATE */
  png_read_start_row(png_structrp png_ptr)
  {
     /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
  
     /* Start of interlace block */
     static const png_byte png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
  
     /* Offset to next interlace block */
     static const png_byte png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
  
     /* Start of interlace block in the y direction */
     static const png_byte png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
  
     /* Offset to next interlace block in the y direction */
     static const png_byte png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
  
     unsigned int max_pixel_depth;
     size_t row_bytes;
  
     png_debug(1, "in png_read_start_row");
  
  #ifdef PNG_READ_TRANSFORMS_SUPPORTED
     png_init_read_transformations(png_ptr);
  #endif
     if (png_ptr->interlaced != 0)
     {
        if ((png_ptr->transformations & PNG_INTERLACE) == 0)
           png_ptr->num_rows = (png_ptr->height + png_pass_yinc[0] - 1 -
               png_pass_ystart[0]) / png_pass_yinc[0];
  
        else
           png_ptr->num_rows = png_ptr->height;
  
        png_ptr->iwidth = (png_ptr->width +
            png_pass_inc[png_ptr->pass] - 1 -
            png_pass_start[png_ptr->pass]) /
            png_pass_inc[png_ptr->pass];
     }
  
     else
     {
        png_ptr->num_rows = png_ptr->height;
        png_ptr->iwidth = png_ptr->width;
     }
  
     max_pixel_depth = (unsigned int)png_ptr->pixel_depth;
  
     /* WARNING: * png_read_transform_info (pngrtran.c) performs a simpler set of
      * calculations to calculate the final pixel depth, then
      * png_do_read_transforms actually does the transforms.  This means that the
      * code which effectively calculates this value is actually repeated in three
      * separate places.  They must all match.  Innocent changes to the order of
      * transformations can and will break libpng in a way that causes memory
      * overwrites.
      *
      * TODO: fix this.
      */
  #ifdef PNG_READ_PACK_SUPPORTED
     if ((png_ptr->transformations & PNG_PACK) != 0 && png_ptr->bit_depth < 8)
        max_pixel_depth = 8;
  #endif
  
  #ifdef PNG_READ_EXPAND_SUPPORTED
     if ((png_ptr->transformations & PNG_EXPAND) != 0)
     {
        if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        {
           if (png_ptr->num_trans != 0)
              max_pixel_depth = 32;
  
           else
              max_pixel_depth = 24;
        }
  
        else if (png_ptr->color_type == PNG_COLOR_TYPE_GRAY)
        {
           if (max_pixel_depth < 8)
              max_pixel_depth = 8;
  
           if (png_ptr->num_trans != 0)
              max_pixel_depth *= 2;
        }
  
        else if (png_ptr->color_type == PNG_COLOR_TYPE_RGB)
        {
           if (png_ptr->num_trans != 0)
           {
              max_pixel_depth *= 4;
              max_pixel_depth /= 3;
           }
        }
     }
  #endif
  
  #ifdef PNG_READ_EXPAND_16_SUPPORTED
     if ((png_ptr->transformations & PNG_EXPAND_16) != 0)
     {
  #  ifdef PNG_READ_EXPAND_SUPPORTED
        /* In fact it is an error if it isn't supported, but checking is
         * the safe way.
         */
        if ((png_ptr->transformations & PNG_EXPAND) != 0)
        {
           if (png_ptr->bit_depth < 16)
              max_pixel_depth *= 2;
        }
        else
  #  endif
        png_ptr->transformations &= ~PNG_EXPAND_16;
     }
  #endif
  
  #ifdef PNG_READ_FILLER_SUPPORTED
     if ((png_ptr->transformations & (PNG_FILLER)) != 0)
     {
        if (png_ptr->color_type == PNG_COLOR_TYPE_GRAY)
        {
           if (max_pixel_depth <= 8)
              max_pixel_depth = 16;
  
           else
              max_pixel_depth = 32;
        }
  
        else if (png_ptr->color_type == PNG_COLOR_TYPE_RGB ||
           png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        {
           if (max_pixel_depth <= 32)
              max_pixel_depth = 32;
  
           else
              max_pixel_depth = 64;
        }
     }
  #endif
  
  #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
     if ((png_ptr->transformations & PNG_GRAY_TO_RGB) != 0)
     {
        if (
  #ifdef PNG_READ_EXPAND_SUPPORTED
            (png_ptr->num_trans != 0 &&
            (png_ptr->transformations & PNG_EXPAND) != 0) ||
  #endif
  #ifdef PNG_READ_FILLER_SUPPORTED
            (png_ptr->transformations & (PNG_FILLER)) != 0 ||
  #endif
            png_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
        {
           if (max_pixel_depth <= 16)
              max_pixel_depth = 32;
  
           else
              max_pixel_depth = 64;
        }
  
        else
        {
           if (max_pixel_depth <= 8)
           {
              if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
                 max_pixel_depth = 32;
  
              else
                 max_pixel_depth = 24;
           }
  
           else if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
              max_pixel_depth = 64;
  
           else
              max_pixel_depth = 48;
        }
     }
  #endif
  
  #if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) && \
  defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
     if ((png_ptr->transformations & PNG_USER_TRANSFORM) != 0)
     {
        unsigned int user_pixel_depth = png_ptr->user_transform_depth *
           png_ptr->user_transform_channels;
  
        if (user_pixel_depth > max_pixel_depth)
           max_pixel_depth = user_pixel_depth;
     }
  #endif
  
     /* This value is stored in png_struct and double checked in the row read
      * code.
      */
     png_ptr->maximum_pixel_depth = (png_byte)max_pixel_depth;
     png_ptr->transformed_pixel_depth = 0; /* calculated on demand */
  
     /* Align the width on the next larger 8 pixels.  Mainly used
      * for interlacing
      */
     row_bytes = ((png_ptr->width + 7) & ~((png_uint_32)7));
     /* Calculate the maximum bytes needed, adding a byte and a pixel
      * for safety's sake
      */
     row_bytes = PNG_ROWBYTES(max_pixel_depth, row_bytes) +
         1 + ((max_pixel_depth + 7) >> 3U);
  
  #ifdef PNG_MAX_MALLOC_64K
     if (row_bytes > (png_uint_32)65536L)
        png_error(png_ptr, "This image requires a row greater than 64KB");
  #endif
  
     if (row_bytes + 48 > png_ptr->old_big_row_buf_size)
     {
        png_free(png_ptr, png_ptr->big_row_buf);
        png_free(png_ptr, png_ptr->big_prev_row);
  
        if (png_ptr->interlaced != 0)
           png_ptr->big_row_buf = (png_bytep)png_calloc(png_ptr,
               row_bytes + 48);
  
        else
           png_ptr->big_row_buf = (png_bytep)png_malloc(png_ptr, row_bytes + 48);
  
        png_ptr->big_prev_row = (png_bytep)png_malloc(png_ptr, row_bytes + 48);
  
  #ifdef PNG_ALIGNED_MEMORY_SUPPORTED
        /* Use 16-byte aligned memory for row_buf with at least 16 bytes
         * of padding before and after row_buf; treat prev_row similarly.
         * NOTE: the alignment is to the start of the pixels, one beyond the start
         * of the buffer, because of the filter byte.  Prior to libpng 1.5.6 this
         * was incorrect; the filter byte was aligned, which had the exact
         * opposite effect of that intended.
         */
        {
           png_bytep temp = png_ptr->big_row_buf + 32;
           int extra = (int)((temp - (png_bytep)0) & 0x0f);
           png_ptr->row_buf = temp - extra - 1/*filter byte*/;
  
           temp = png_ptr->big_prev_row + 32;
           extra = (int)((temp - (png_bytep)0) & 0x0f);
           png_ptr->prev_row = temp - extra - 1/*filter byte*/;
        }
  
  #else
        /* Use 31 bytes of padding before and 17 bytes after row_buf. */
        png_ptr->row_buf = png_ptr->big_row_buf + 31;
        png_ptr->prev_row = png_ptr->big_prev_row + 31;
  #endif
        png_ptr->old_big_row_buf_size = row_bytes + 48;
     }
  
  #ifdef PNG_MAX_MALLOC_64K
     if (png_ptr->rowbytes > 65535)
        png_error(png_ptr, "This image requires a row greater than 64KB");
  
  #endif
     if (png_ptr->rowbytes > (PNG_SIZE_MAX - 1))
        png_error(png_ptr, "Row has too many bytes to allocate in memory");
  
     memset(png_ptr->prev_row, 0, png_ptr->rowbytes + 1);
  
     png_debug1(3, "width = %u,", png_ptr->width);
     png_debug1(3, "height = %u,", png_ptr->height);
     png_debug1(3, "iwidth = %u,", png_ptr->iwidth);
     png_debug1(3, "num_rows = %u,", png_ptr->num_rows);
     png_debug1(3, "rowbytes = %lu,", (unsigned long)png_ptr->rowbytes);
     png_debug1(3, "irowbytes = %lu",
         (unsigned long)PNG_ROWBYTES(png_ptr->pixel_depth, png_ptr->iwidth) + 1);
  
     /* The sequential reader needs a buffer for IDAT, but the progressive reader
      * does not, so free the read buffer now regardless; the sequential reader
      * reallocates it on demand.
      */
     if (png_ptr->read_buffer != NULL)
     {
        png_bytep buffer = png_ptr->read_buffer;
  
        png_ptr->read_buffer_size = 0;
        png_ptr->read_buffer = NULL;
        png_free(png_ptr, buffer);
     }
  
     /* Finally claim the zstream for the inflate of the IDAT data, use the bits
      * value from the stream (note that this will result in a fatal error if the
      * IDAT stream has a bogus deflate header window_bits value, but this should
      * not be happening any longer!)
      */
     if (png_inflate_claim(png_ptr, png_IDAT) != Z_OK)
        png_error(png_ptr, png_ptr->zstream.msg);
  
     png_ptr->flags |= PNG_FLAG_ROW_INIT;
  }
  
  #ifdef PNG_READ_APNG_SUPPORTED
  /* This function is to be called after the main IDAT set has been read and
   * before a new IDAT is read. It resets some parts of png_ptr
   * to make them usable by the read functions again */
  void /* PRIVATE */
  png_read_reset(png_structp png_ptr)
  {
      png_ptr->mode &= ~PNG_HAVE_IDAT;
      png_ptr->mode &= ~PNG_AFTER_IDAT;
      png_ptr->row_number = 0;
      png_ptr->pass = 0;
  }
  
  void /* PRIVATE */
  png_read_reinit(png_structp png_ptr, png_infop info_ptr)
  {
      png_ptr->width = info_ptr->next_frame_width;
      png_ptr->height = info_ptr->next_frame_height;
      png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth,png_ptr->width);
      png_ptr->info_rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth,
          png_ptr->width);
      if (png_ptr->prev_row)
          memset(png_ptr->prev_row, 0, png_ptr->rowbytes + 1);
  }
  
  #ifdef PNG_PROGRESSIVE_READ_SUPPORTED
  /* same as png_read_reset() but for the progressive reader */
  void /* PRIVATE */
  png_progressive_read_reset(png_structp png_ptr)
  {
  #ifdef PNG_READ_INTERLACING_SUPPORTED
     /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
  
     /* Start of interlace block */
      const int png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};
  
      /* Offset to next interlace block */
      const int png_pass_inc[] = {8, 8, 4, 4, 2, 2, 1};
  
      /* Start of interlace block in the y direction */
      const int png_pass_ystart[] = {0, 0, 4, 0, 2, 0, 1};
  
      /* Offset to next interlace block in the y direction */
      const int png_pass_yinc[] = {8, 8, 8, 4, 4, 2, 2};
  
      if (png_ptr->interlaced)
      {
          if (!(png_ptr->transformations & PNG_INTERLACE))
              png_ptr->num_rows = (png_ptr->height + png_pass_yinc[0] - 1 -
                                  png_pass_ystart[0]) / png_pass_yinc[0];
          else
              png_ptr->num_rows = png_ptr->height;
  
          png_ptr->iwidth = (png_ptr->width +
                             png_pass_inc[png_ptr->pass] - 1 -
                             png_pass_start[png_ptr->pass]) /
                             png_pass_inc[png_ptr->pass];
      }
      else
  #endif /* PNG_READ_INTERLACING_SUPPORTED */
      {
          png_ptr->num_rows = png_ptr->height;
          png_ptr->iwidth = png_ptr->width;
      }
      png_ptr->flags &= ~PNG_FLAG_ZSTREAM_ENDED;
      if (inflateReset(&(png_ptr->zstream)) != Z_OK)
          png_error(png_ptr, "inflateReset failed");
      png_ptr->zstream.avail_in = 0;
      png_ptr->zstream.next_in = 0;
      png_ptr->zstream.next_out = png_ptr->row_buf;
      png_ptr->zstream.avail_out = (uInt)PNG_ROWBYTES(png_ptr->pixel_depth,
          png_ptr->iwidth) + 1;
  }
  #endif /* PNG_PROGRESSIVE_READ_SUPPORTED */
  #endif /* PNG_READ_APNG_SUPPORTED */
  #endif /* READ */
  