text: #pragma warning( disable : 4244 )
  
  /* pngwutil.c - utilities to write a PNG file
   *
   * libpng version 1.2.8 - December 3, 2004
   * For conditions of distribution and use, see copyright notice in png.h
   * Copyright (c) 1998-2004 Glenn Randers-Pehrson
   * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
   * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
   */
  
  #define PNG_INTERNAL
  #include "png.h"
  #ifdef PNG_WRITE_SUPPORTED
  
  /* Place a 32-bit number into a buffer in PNG byte order.  We work
   * with unsigned numbers for convenience, although one supported
   * ancillary chunk uses signed (two's complement) numbers.
   */
  void /* PRIVATE */
  png_save_uint_32(png_bytep buf, png_uint_32 i)
  {
     buf[0] = (png_byte)((i >> 24) & 0xff);
     buf[1] = (png_byte)((i >> 16) & 0xff);
     buf[2] = (png_byte)((i >> 8) & 0xff);
     buf[3] = (png_byte)(i & 0xff);
  }
  
  #if defined(PNG_WRITE_pCAL_SUPPORTED) || defined(PNG_WRITE_oFFs_SUPPORTED)
  /* The png_save_int_32 function assumes integers are stored in two's
   * complement format.  If this isn't the case, then this routine needs to
   * be modified to write data in two's complement format.
   */
  void /* PRIVATE */
  png_save_int_32(png_bytep buf, png_int_32 i)
  {
     buf[0] = (png_byte)((i >> 24) & 0xff);
     buf[1] = (png_byte)((i >> 16) & 0xff);
     buf[2] = (png_byte)((i >> 8) & 0xff);
     buf[3] = (png_byte)(i & 0xff);
  }
  #endif
  
  /* Place a 16-bit number into a buffer in PNG byte order.
   * The parameter is declared unsigned int, not png_uint_16,
   * just to avoid potential problems on pre-ANSI C compilers.
   */
  void /* PRIVATE */
  png_save_uint_16(png_bytep buf, unsigned int i)
  {
     buf[0] = (png_byte)((i >> 8) & 0xff);
     buf[1] = (png_byte)(i & 0xff);
  }
  
  /* Write a PNG chunk all at once.  The type is an array of ASCII characters
   * representing the chunk name.  The array must be at least 4 bytes in
   * length, and does not need to be null terminated.  To be safe, pass the
   * pre-defined chunk names here, and if you need a new one, define it
   * where the others are defined.  The length is the length of the data.
   * All the data must be present.  If that is not possible, use the
   * png_write_chunk_start(), png_write_chunk_data(), and png_write_chunk_end()
   * functions instead.
   */
  void PNGAPI
  png_write_chunk(png_structp png_ptr, png_bytep chunk_name,
     png_bytep data, png_size_t length)
  {
     png_write_chunk_start(png_ptr, chunk_name, (png_uint_32)length);
     png_write_chunk_data(png_ptr, data, length);
     png_write_chunk_end(png_ptr);
  }
  
  /* Write the start of a PNG chunk.  The type is the chunk type.
   * The total_length is the sum of the lengths of all the data you will be
   * passing in png_write_chunk_data().
   */
  void PNGAPI
  png_write_chunk_start(png_structp png_ptr, png_bytep chunk_name,
     png_uint_32 length)
  {
     png_byte buf[4];
     png_debug2(0, "Writing %s chunk (%lu bytes)\n", chunk_name, length);
  
     /* write the length */
     png_save_uint_32(buf, length);
     png_write_data(png_ptr, buf, (png_size_t)4);
  
     /* write the chunk name */
     png_write_data(png_ptr, chunk_name, (png_size_t)4);
     /* reset the crc and run it over the chunk name */
     png_reset_crc(png_ptr);
     png_calculate_crc(png_ptr, chunk_name, (png_size_t)4);
  }
  
  /* Write the data of a PNG chunk started with png_write_chunk_start().
   * Note that multiple calls to this function are allowed, and that the
   * sum of the lengths from these calls *must* add up to the total_length
   * given to png_write_chunk_start().
   */
  void PNGAPI
  png_write_chunk_data(png_structp png_ptr, png_bytep data, png_size_t length)
  {
     /* write the data, and run the CRC over it */
     if (data != NULL && length > 0)
     {
        png_calculate_crc(png_ptr, data, length);
        png_write_data(png_ptr, data, length);
     }
  }
  
  /* Finish a chunk started with png_write_chunk_start(). */
  void PNGAPI
  png_write_chunk_end(png_structp png_ptr)
  {
     png_byte buf[4];
  
     /* write the crc */
     png_save_uint_32(buf, png_ptr->crc);
  
     png_write_data(png_ptr, buf, (png_size_t)4);
  }
  
  /* Simple function to write the signature.  If we have already written
   * the magic bytes of the signature, or more likely, the PNG stream is
   * being embedded into another stream and doesn't need its own signature,
   * we should call png_set_sig_bytes() to tell libpng how many of the
   * bytes have already been written.
   */
  void /* PRIVATE */
  png_write_sig(png_structp png_ptr)
  {
     png_byte png_signature[8] = {137, 80, 78, 71, 13, 10, 26, 10};
     /* write the rest of the 8 byte signature */
     png_write_data(png_ptr, &png_signature[png_ptr->sig_bytes],
        (png_size_t)8 - png_ptr->sig_bytes);
     if(png_ptr->sig_bytes < 3)
        png_ptr->mode |= PNG_HAVE_PNG_SIGNATURE;
  }
  
  #if defined(PNG_WRITE_TEXT_SUPPORTED) || defined(PNG_WRITE_iCCP_SUPPORTED)
  /*
   * This pair of functions encapsulates the operation of (a) compressing a
   * text string, and (b) issuing it later as a series of chunk data writes.
   * The compression_state structure is shared context for these functions
   * set up by the caller in order to make the whole mess thread-safe.
   */
  
  typedef struct
  {
      char *input;   /* the uncompressed input data */
      int input_len;   /* its length */
      int num_output_ptr; /* number of output pointers used */
      int max_output_ptr; /* size of output_ptr */
      png_charpp output_ptr; /* array of pointers to output */
  } compression_state;
  
  /* compress given text into storage in the png_ptr structure */
  static int /* PRIVATE */
  png_text_compress(png_structp png_ptr,
          png_charp text, png_size_t text_len, int compression,
          compression_state *comp)
  {
     int ret;
  
     comp->num_output_ptr = comp->max_output_ptr = 0;
     comp->output_ptr = NULL;
     comp->input = NULL;
  
     /* we may just want to pass the text right through */
     if (compression == PNG_TEXT_COMPRESSION_NONE)
     {
         comp->input = text;
         comp->input_len = text_len;
         return((int)text_len);
     }
  
     if (compression >= PNG_TEXT_COMPRESSION_LAST)
     {
  #if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
        char msg[50];
        sprintf(msg, "Unknown compression type %d", compression);
        png_warning(png_ptr, msg);
  #else
        png_warning(png_ptr, "Unknown compression type");
  #endif
     }
  
     /* We can't write the chunk until we find out how much data we have,
      * which means we need to run the compressor first and save the
      * output.  This shouldn't be a problem, as the vast majority of
      * comments should be reasonable, but we will set up an array of
      * malloc'd pointers to be sure.
      *
      * If we knew the application was well behaved, we could simplify this
      * greatly by assuming we can always malloc an output buffer large
      * enough to hold the compressed text ((1001 * text_len / 1000) + 12)
      * and malloc this directly.  The only time this would be a bad idea is
      * if we can't malloc more than 64K and we have 64K of random input
      * data, or if the input string is incredibly large (although this
      * wouldn't cause a failure, just a slowdown due to swapping).
      */
  
     /* set up the compression buffers */
     png_ptr->zstream.avail_in = (uInt)text_len;
     png_ptr->zstream.next_in = (Bytef *)text;
     png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
     png_ptr->zstream.next_out = (Bytef *)png_ptr->zbuf;
  
     /* this is the same compression loop as in png_write_row() */
     do
     {
        /* compress the data */
        ret = deflate(&png_ptr->zstream, Z_NO_FLUSH);
        if (ret != Z_OK)
        {
           /* error */
           if (png_ptr->zstream.msg != NULL)
              png_error(png_ptr, png_ptr->zstream.msg);
           else
              png_error(png_ptr, "zlib error");
        }
        /* check to see if we need more room */
        if (!(png_ptr->zstream.avail_out))
        {
           /* make sure the output array has room */
           if (comp->num_output_ptr >= comp->max_output_ptr)
           {
              int old_max;
  
              old_max = comp->max_output_ptr;
              comp->max_output_ptr = comp->num_output_ptr + 4;
              if (comp->output_ptr != NULL)
              {
                 png_charpp old_ptr;
  
                 old_ptr = comp->output_ptr;
                 comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                    (png_uint_32)(comp->max_output_ptr *
                    png_sizeof (png_charpp)));
                 png_memcpy(comp->output_ptr, old_ptr, old_max
                    * png_sizeof (png_charp));
                 png_free(png_ptr, old_ptr);
              }
              else
                 comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                    (png_uint_32)(comp->max_output_ptr *
                    png_sizeof (png_charp)));
           }
  
           /* save the data */
           comp->output_ptr[comp->num_output_ptr] = (png_charp)png_malloc(png_ptr,
              (png_uint_32)png_ptr->zbuf_size);
           png_memcpy(comp->output_ptr[comp->num_output_ptr], png_ptr->zbuf,
              png_ptr->zbuf_size);
           comp->num_output_ptr++;
  
           /* and reset the buffer */
           png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
           png_ptr->zstream.next_out = png_ptr->zbuf;
        }
     /* continue until we don't have any more to compress */
     } while (png_ptr->zstream.avail_in);
  
     /* finish the compression */
     do
     {
        /* tell zlib we are finished */
        ret = deflate(&png_ptr->zstream, Z_FINISH);
  
        if (ret == Z_OK)
        {
           /* check to see if we need more room */
           if (!(png_ptr->zstream.avail_out))
           {
              /* check to make sure our output array has room */
              if (comp->num_output_ptr >= comp->max_output_ptr)
              {
                 int old_max;
  
                 old_max = comp->max_output_ptr;
                 comp->max_output_ptr = comp->num_output_ptr + 4;
                 if (comp->output_ptr != NULL)
                 {
                    png_charpp old_ptr;
  
                    old_ptr = comp->output_ptr;
                    /* This could be optimized to realloc() */
                    comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                       (png_uint_32)(comp->max_output_ptr *
                       png_sizeof (png_charpp)));
                    png_memcpy(comp->output_ptr, old_ptr,
                       old_max * png_sizeof (png_charp));
                    png_free(png_ptr, old_ptr);
                 }
                 else
                    comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                       (png_uint_32)(comp->max_output_ptr *
                       png_sizeof (png_charp)));
              }
  
              /* save off the data */
              comp->output_ptr[comp->num_output_ptr] =
                 (png_charp)png_malloc(png_ptr, (png_uint_32)png_ptr->zbuf_size);
              png_memcpy(comp->output_ptr[comp->num_output_ptr], png_ptr->zbuf,
                 png_ptr->zbuf_size);
              comp->num_output_ptr++;
  
              /* and reset the buffer pointers */
              png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
              png_ptr->zstream.next_out = png_ptr->zbuf;
           }
        }
        else if (ret != Z_STREAM_END)
        {
           /* we got an error */
           if (png_ptr->zstream.msg != NULL)
              png_error(png_ptr, png_ptr->zstream.msg);
           else
              png_error(png_ptr, "zlib error");
        }
     } while (ret != Z_STREAM_END);
  
     /* text length is number of buffers plus last buffer */
     text_len = png_ptr->zbuf_size * comp->num_output_ptr;
     if (png_ptr->zstream.avail_out < png_ptr->zbuf_size)
        text_len += png_ptr->zbuf_size - (png_size_t)png_ptr->zstream.avail_out;
  
     return((int)text_len);
  }
  
  /* ship the compressed text out via chunk writes */
  static void /* PRIVATE */
  png_write_compressed_data_out(png_structp png_ptr, compression_state *comp)
  {
     int i;
  
     /* handle the no-compression case */
     if (comp->input)
     {
         png_write_chunk_data(png_ptr, (png_bytep)comp->input,
                              (png_size_t)comp->input_len);
         return;
     }
  
     /* write saved output buffers, if any */
     for (i = 0; i < comp->num_output_ptr; i++)
     {
        png_write_chunk_data(png_ptr,(png_bytep)comp->output_ptr[i],
           png_ptr->zbuf_size);
        png_free(png_ptr, comp->output_ptr[i]);
        comp->output_ptr[i]=NULL;
     }
     if (comp->max_output_ptr != 0)
        png_free(png_ptr, comp->output_ptr);
        comp->output_ptr=NULL;
     /* write anything left in zbuf */
     if (png_ptr->zstream.avail_out < (png_uint_32)png_ptr->zbuf_size)
        png_write_chunk_data(png_ptr, png_ptr->zbuf,
           png_ptr->zbuf_size - png_ptr->zstream.avail_out);
  
     /* reset zlib for another zTXt/iTXt or image data */
     deflateReset(&png_ptr->zstream);
     png_ptr->zstream.data_type = Z_BINARY;
  }
  #endif
  
  /* Write the IHDR chunk, and update the png_struct with the necessary
   * information.  Note that the rest of this code depends upon this
   * information being correct.
   */
  void /* PRIVATE */
  png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
     int bit_depth, int color_type, int compression_type, int filter_type,
     int interlace_type)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_IHDR;
  #endif
     png_byte buf[13]; /* buffer to store the IHDR info */
  
     png_debug(1, "in png_write_IHDR\n");
     /* Check that we have valid input data from the application info */
     switch (color_type)
     {
        case PNG_COLOR_TYPE_GRAY:
           switch (bit_depth)
           {
              case 1:
              case 2:
              case 4:
              case 8:
              case 16: png_ptr->channels = 1; break;
              default: png_error(png_ptr,"Invalid bit depth for grayscale image");
           }
           break;
        case PNG_COLOR_TYPE_RGB:
           if (bit_depth != 8 && bit_depth != 16)
              png_error(png_ptr, "Invalid bit depth for RGB image");
           png_ptr->channels = 3;
           break;
        case PNG_COLOR_TYPE_PALETTE:
           switch (bit_depth)
           {
              case 1:
              case 2:
              case 4:
              case 8: png_ptr->channels = 1; break;
              default: png_error(png_ptr, "Invalid bit depth for paletted image");
           }
           break;
        case PNG_COLOR_TYPE_GRAY_ALPHA:
           if (bit_depth != 8 && bit_depth != 16)
              png_error(png_ptr, "Invalid bit depth for grayscale+alpha image");
           png_ptr->channels = 2;
           break;
        case PNG_COLOR_TYPE_RGB_ALPHA:
           if (bit_depth != 8 && bit_depth != 16)
              png_error(png_ptr, "Invalid bit depth for RGBA image");
           png_ptr->channels = 4;
           break;
        default:
           png_error(png_ptr, "Invalid image color type specified");
     }
  
     if (compression_type != PNG_COMPRESSION_TYPE_BASE)
     {
        png_warning(png_ptr, "Invalid compression type specified");
        compression_type = PNG_COMPRESSION_TYPE_BASE;
     }
  
     /* Write filter_method 64 (intrapixel differencing) only if
      * 1. Libpng was compiled with PNG_MNG_FEATURES_SUPPORTED and
      * 2. Libpng did not write a PNG signature (this filter_method is only
      *    used in PNG datastreams that are embedded in MNG datastreams) and
      * 3. The application called png_permit_mng_features with a mask that
      *    included PNG_FLAG_MNG_FILTER_64 and
      * 4. The filter_method is 64 and
      * 5. The color_type is RGB or RGBA
      */
     if (
  #if defined(PNG_MNG_FEATURES_SUPPORTED)
        !((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
        ((png_ptr->mode&PNG_HAVE_PNG_SIGNATURE) == 0) &&
        (color_type == PNG_COLOR_TYPE_RGB ||
         color_type == PNG_COLOR_TYPE_RGB_ALPHA) &&
        (filter_type == PNG_INTRAPIXEL_DIFFERENCING)) &&
  #endif
        filter_type != PNG_FILTER_TYPE_BASE)
     {
        png_warning(png_ptr, "Invalid filter type specified");
        filter_type = PNG_FILTER_TYPE_BASE;
     }
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     if (interlace_type != PNG_INTERLACE_NONE &&
        interlace_type != PNG_INTERLACE_ADAM7)
     {
        png_warning(png_ptr, "Invalid interlace type specified");
        interlace_type = PNG_INTERLACE_ADAM7;
     }
  #else
     interlace_type=PNG_INTERLACE_NONE;
  #endif
  
     /* save off the relevent information */
     png_ptr->bit_depth = (png_byte)bit_depth;
     png_ptr->color_type = (png_byte)color_type;
     png_ptr->interlaced = (png_byte)interlace_type;
  #if defined(PNG_MNG_FEATURES_SUPPORTED)
     png_ptr->filter_type = (png_byte)filter_type;
  #endif
     png_ptr->compression_type = (png_byte)compression_type;
     png_ptr->width = width;
     png_ptr->height = height;
  
     png_ptr->pixel_depth = (png_byte)(bit_depth * png_ptr->channels);
     png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth, width);
     /* set the usr info, so any transformations can modify it */
     png_ptr->usr_width = png_ptr->width;
     png_ptr->usr_bit_depth = png_ptr->bit_depth;
     png_ptr->usr_channels = png_ptr->channels;
  
     /* pack the header information into the buffer */
     png_save_uint_32(buf, width);
     png_save_uint_32(buf + 4, height);
     buf[8] = (png_byte)bit_depth;
     buf[9] = (png_byte)color_type;
     buf[10] = (png_byte)compression_type;
     buf[11] = (png_byte)filter_type;
     buf[12] = (png_byte)interlace_type;
  
     /* write the chunk */
     png_write_chunk(png_ptr, (png_bytep)png_IHDR, buf, (png_size_t)13);
  
     /* initialize zlib with PNG info */
     png_ptr->zstream.zalloc = png_zalloc;
     png_ptr->zstream.zfree = png_zfree;
     png_ptr->zstream.opaque = (voidpf)png_ptr;
     if (!(png_ptr->do_filter))
     {
        if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
           png_ptr->bit_depth < 8)
           png_ptr->do_filter = PNG_FILTER_NONE;
        else
           png_ptr->do_filter = PNG_ALL_FILTERS;
     }
     if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_STRATEGY))
     {
        if (png_ptr->do_filter != PNG_FILTER_NONE)
           png_ptr->zlib_strategy = Z_FILTERED;
        else
           png_ptr->zlib_strategy = Z_DEFAULT_STRATEGY;
     }
     if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_LEVEL))
        png_ptr->zlib_level = Z_DEFAULT_COMPRESSION;
     if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_MEM_LEVEL))
        png_ptr->zlib_mem_level = 8;
     if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_WINDOW_BITS))
        png_ptr->zlib_window_bits = 15;
     if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_METHOD))
        png_ptr->zlib_method = 8;
     deflateInit2(&png_ptr->zstream, png_ptr->zlib_level,
        png_ptr->zlib_method, png_ptr->zlib_window_bits,
        png_ptr->zlib_mem_level, png_ptr->zlib_strategy);
     png_ptr->zstream.next_out = png_ptr->zbuf;
     png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
     /* libpng is not interested in zstream.data_type */
     /* set it to a predefined value, to avoid its evaluation inside zlib */
     png_ptr->zstream.data_type = Z_BINARY;
  
     png_ptr->mode = PNG_HAVE_IHDR;
  }
  
  /* write the palette.  We are careful not to trust png_color to be in the
   * correct order for PNG, so people can redefine it to any convenient
   * structure.
   */
  void /* PRIVATE */
  png_write_PLTE(png_structp png_ptr, png_colorp palette, png_uint_32 num_pal)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_PLTE;
  #endif
     png_uint_32 i;
     png_colorp pal_ptr;
     png_byte buf[3];
  
     png_debug(1, "in png_write_PLTE\n");
     if ((
  #if defined(PNG_MNG_FEATURES_SUPPORTED)
          !(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE) &&
  #endif
          num_pal == 0) || num_pal > 256)
     {
       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       {
          png_error(png_ptr, "Invalid number of colors in palette");
       }
       else
       {
          png_warning(png_ptr, "Invalid number of colors in palette");
          return;
       }
     }
  
     if (!(png_ptr->color_type&PNG_COLOR_MASK_COLOR))
     {
        png_warning(png_ptr,
          "Ignoring request to write a PLTE chunk in grayscale PNG");
        return;
     }
  
     png_ptr->num_palette = (png_uint_16)num_pal;
     png_debug1(3, "num_palette = %d\n", png_ptr->num_palette);
  
     png_write_chunk_start(png_ptr, (png_bytep)png_PLTE, num_pal * 3);
  #ifndef PNG_NO_POINTER_INDEXING
     for (i = 0, pal_ptr = palette; i < num_pal; i++, pal_ptr++)
     {
        buf[0] = pal_ptr->red;
        buf[1] = pal_ptr->green;
        buf[2] = pal_ptr->blue;
        png_write_chunk_data(png_ptr, buf, (png_size_t)3);
     }
  #else
     /* This is a little slower but some buggy compilers need to do this instead */
     pal_ptr=palette;
     for (i = 0; i < num_pal; i++)
     {
        buf[0] = pal_ptr[i].red;
        buf[1] = pal_ptr[i].green;
        buf[2] = pal_ptr[i].blue;
        png_write_chunk_data(png_ptr, buf, (png_size_t)3);
     }
  #endif
     png_write_chunk_end(png_ptr);
     png_ptr->mode |= PNG_HAVE_PLTE;
  }
  
  /* write an IDAT chunk */
  void /* PRIVATE */
  png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_IDAT;
  #endif
     png_debug(1, "in png_write_IDAT\n");
  
     /* Optimize the CMF field in the zlib stream. */
     /* This hack of the zlib stream is compliant to the stream specification. */
     if (!(png_ptr->mode & PNG_HAVE_IDAT) &&
         png_ptr->compression_type == PNG_COMPRESSION_TYPE_BASE)
     {
        unsigned int z_cmf = data[0];  /* zlib compression method and flags */
        if ((z_cmf & 0x0f) == 8 && (z_cmf & 0xf0) <= 0x70)
        {
           /* Avoid memory underflows and multiplication overflows. */
           /* The conditions below are practically always satisfied;
              however, they still must be checked. */
           if (length >= 2 &&
               png_ptr->height < 16384 && png_ptr->width < 16384)
           {
              png_uint_32 uncompressed_idat_size = png_ptr->height *
                 ((png_ptr->width *
                 png_ptr->channels * png_ptr->bit_depth + 15) >> 3);
              unsigned int z_cinfo = z_cmf >> 4;
              unsigned int half_z_window_size = 1 << (z_cinfo + 7);
              while (uncompressed_idat_size <= half_z_window_size &&
                     half_z_window_size >= 256)
              {
                 z_cinfo--;
                 half_z_window_size >>= 1;
              }
              z_cmf = (z_cmf & 0x0f) | (z_cinfo << 4);
              if (data[0] != (png_byte)z_cmf)
              {
                 data[0] = (png_byte)z_cmf;
                 data[1] &= 0xe0;
                 data[1] += (png_byte)(0x1f - ((z_cmf << 8) + data[1]) % 0x1f);
              }
           }
        }
        else
           png_error(png_ptr,
              "Invalid zlib compression method or flags in IDAT");
     }
  
     png_write_chunk(png_ptr, (png_bytep)png_IDAT, data, length);
     png_ptr->mode |= PNG_HAVE_IDAT;
  }
  
  /* write an IEND chunk */
  void /* PRIVATE */
  png_write_IEND(png_structp png_ptr)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_IEND;
  #endif
     png_debug(1, "in png_write_IEND\n");
     png_write_chunk(png_ptr, (png_bytep)png_IEND, png_bytep_NULL,
       (png_size_t)0);
     png_ptr->mode |= PNG_HAVE_IEND;
  }
  
  #if defined(PNG_WRITE_gAMA_SUPPORTED)
  /* write a gAMA chunk */
  #ifdef PNG_FLOATING_POINT_SUPPORTED
  void /* PRIVATE */
  png_write_gAMA(png_structp png_ptr, double file_gamma)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_gAMA;
  #endif
     png_uint_32 igamma;
     png_byte buf[4];
  
     png_debug(1, "in png_write_gAMA\n");
     /* file_gamma is saved in 1/100,000ths */
     igamma = (png_uint_32)(file_gamma * 100000.0 + 0.5);
     png_save_uint_32(buf, igamma);
     png_write_chunk(png_ptr, (png_bytep)png_gAMA, buf, (png_size_t)4);
  }
  #endif
  #ifdef PNG_FIXED_POINT_SUPPORTED
  void /* PRIVATE */
  png_write_gAMA_fixed(png_structp png_ptr, png_fixed_point file_gamma)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_gAMA;
  #endif
     png_byte buf[4];
  
     png_debug(1, "in png_write_gAMA\n");
     /* file_gamma is saved in 1/100,000ths */
     png_save_uint_32(buf, (png_uint_32)file_gamma);
     png_write_chunk(png_ptr, (png_bytep)png_gAMA, buf, (png_size_t)4);
  }
  #endif
  #endif
  
  #if defined(PNG_WRITE_sRGB_SUPPORTED)
  /* write a sRGB chunk */
  void /* PRIVATE */
  png_write_sRGB(png_structp png_ptr, int srgb_intent)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_sRGB;
  #endif
     png_byte buf[1];
  
     png_debug(1, "in png_write_sRGB\n");
     if(srgb_intent >= PNG_sRGB_INTENT_LAST)
           png_warning(png_ptr,
              "Invalid sRGB rendering intent specified");
     buf[0]=(png_byte)srgb_intent;
     png_write_chunk(png_ptr, (png_bytep)png_sRGB, buf, (png_size_t)1);
  }
  #endif
  
  #if defined(PNG_WRITE_iCCP_SUPPORTED)
  /* write an iCCP chunk */
  void /* PRIVATE */
  png_write_iCCP(png_structp png_ptr, png_charp name, int compression_type,
     png_charp profile, int profile_len)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_iCCP;
  #endif
     png_size_t name_len;
     png_charp new_name;
     compression_state comp;
  
     png_debug(1, "in png_write_iCCP\n");
     if (name == NULL || (name_len = png_check_keyword(png_ptr, name,
        &new_name)) == 0)
     {
        png_warning(png_ptr, "Empty keyword in iCCP chunk");
        return;
     }
  
     if (compression_type != PNG_COMPRESSION_TYPE_BASE)
        png_warning(png_ptr, "Unknown compression type in iCCP chunk");
  
     if (profile == NULL)
        profile_len = 0;
  
     if (profile_len)
         profile_len = png_text_compress(png_ptr, profile, (png_size_t)profile_len,
            PNG_COMPRESSION_TYPE_BASE, &comp);
  
     /* make sure we include the NULL after the name and the compression type */
     png_write_chunk_start(png_ptr, (png_bytep)png_iCCP,
            (png_uint_32)name_len+profile_len+2);
     new_name[name_len+1]=0x00;
     png_write_chunk_data(png_ptr, (png_bytep)new_name, name_len + 2);
  
     if (profile_len)
        png_write_compressed_data_out(png_ptr, &comp);
  
     png_write_chunk_end(png_ptr);
     png_free(png_ptr, new_name);
  }
  #endif
  
  #if defined(PNG_WRITE_sPLT_SUPPORTED)
  /* write a sPLT chunk */
  void /* PRIVATE */
  png_write_sPLT(png_structp png_ptr, png_sPLT_tp spalette)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_sPLT;
  #endif
     png_size_t name_len;
     png_charp new_name;
     png_byte entrybuf[10];
     int entry_size = (spalette->depth == 8 ? 6 : 10);
     int palette_size = entry_size * spalette->nentries;
     png_sPLT_entryp ep;
  #ifdef PNG_NO_POINTER_INDEXING
     int i;
  #endif
  
     png_debug(1, "in png_write_sPLT\n");
     if (spalette->name == NULL || (name_len = png_check_keyword(png_ptr,
        spalette->name, &new_name))==0)
     {
        png_warning(png_ptr, "Empty keyword in sPLT chunk");
        return;
     }
  
     /* make sure we include the NULL after the name */
     png_write_chunk_start(png_ptr, (png_bytep)png_sPLT,
            (png_uint_32)(name_len + 2 + palette_size));
     png_write_chunk_data(png_ptr, (png_bytep)new_name, name_len + 1);
     png_write_chunk_data(png_ptr, (png_bytep)&spalette->depth, 1);
  
     /* loop through each palette entry, writing appropriately */
  #ifndef PNG_NO_POINTER_INDEXING
     for (ep = spalette->entries; ep<spalette->entries+spalette->nentries; ep++)
     {
         if (spalette->depth == 8)
         {
             entrybuf[0] = (png_byte)ep->red;
             entrybuf[1] = (png_byte)ep->green;
             entrybuf[2] = (png_byte)ep->blue;
             entrybuf[3] = (png_byte)ep->alpha;
             png_save_uint_16(entrybuf + 4, ep->frequency);
         }
         else
         {
             png_save_uint_16(entrybuf + 0, ep->red);
             png_save_uint_16(entrybuf + 2, ep->green);
             png_save_uint_16(entrybuf + 4, ep->blue);
             png_save_uint_16(entrybuf + 6, ep->alpha);
             png_save_uint_16(entrybuf + 8, ep->frequency);
         }
         png_write_chunk_data(png_ptr, entrybuf, (png_size_t)entry_size);
     }
  #else
     ep=spalette->entries;
     for (i=0; i>spalette->nentries; i++)
     {
         if (spalette->depth == 8)
         {
             entrybuf[0] = (png_byte)ep[i].red;
             entrybuf[1] = (png_byte)ep[i].green;
             entrybuf[2] = (png_byte)ep[i].blue;
             entrybuf[3] = (png_byte)ep[i].alpha;
             png_save_uint_16(entrybuf + 4, ep[i].frequency);
         }
         else
         {
             png_save_uint_16(entrybuf + 0, ep[i].red);
             png_save_uint_16(entrybuf + 2, ep[i].green);
             png_save_uint_16(entrybuf + 4, ep[i].blue);
             png_save_uint_16(entrybuf + 6, ep[i].alpha);
             png_save_uint_16(entrybuf + 8, ep[i].frequency);
         }
         png_write_chunk_data(png_ptr, entrybuf, entry_size);
     }
  #endif
  
     png_write_chunk_end(png_ptr);
     png_free(png_ptr, new_name);
  }
  #endif
  
  #if defined(PNG_WRITE_sBIT_SUPPORTED)
  /* write the sBIT chunk */
  void /* PRIVATE */
  png_write_sBIT(png_structp png_ptr, png_color_8p sbit, int color_type)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_sBIT;
  #endif
     png_byte buf[4];
     png_size_t size;
  
     png_debug(1, "in png_write_sBIT\n");
     /* make sure we don't depend upon the order of PNG_COLOR_8 */
     if (color_type & PNG_COLOR_MASK_COLOR)
     {
        png_byte maxbits;
  
        maxbits = (png_byte)(color_type==PNG_COLOR_TYPE_PALETTE ? 8 :
                  png_ptr->usr_bit_depth);
        if (sbit->red == 0 || sbit->red > maxbits ||
            sbit->green == 0 || sbit->green > maxbits ||
            sbit->blue == 0 || sbit->blue > maxbits)
        {
           png_warning(png_ptr, "Invalid sBIT depth specified");
           return;
        }
        buf[0] = sbit->red;
        buf[1] = sbit->green;
        buf[2] = sbit->blue;
        size = 3;
     }
     else
     {
        if (sbit->gray == 0 || sbit->gray > png_ptr->usr_bit_depth)
        {
           png_warning(png_ptr, "Invalid sBIT depth specified");
           return;
        }
        buf[0] = sbit->gray;
        size = 1;
     }
  
     if (color_type & PNG_COLOR_MASK_ALPHA)
     {
        if (sbit->alpha == 0 || sbit->alpha > png_ptr->usr_bit_depth)
        {
           png_warning(png_ptr, "Invalid sBIT depth specified");
           return;
        }
        buf[size++] = sbit->alpha;
     }
  
     png_write_chunk(png_ptr, (png_bytep)png_sBIT, buf, size);
  }
  #endif
  
  #if defined(PNG_WRITE_cHRM_SUPPORTED)
  /* write the cHRM chunk */
  #ifdef PNG_FLOATING_POINT_SUPPORTED
  void /* PRIVATE */
  png_write_cHRM(png_structp png_ptr, double white_x, double white_y,
     double red_x, double red_y, double green_x, double green_y,
     double blue_x, double blue_y)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_cHRM;
  #endif
     png_byte buf[32];
     png_uint_32 itemp;
  
     png_debug(1, "in png_write_cHRM\n");
     /* each value is saved in 1/100,000ths */
     if (white_x < 0 || white_x > 0.8 || white_y < 0 || white_y > 0.8 ||
         white_x + white_y > 1.0)
     {
        png_warning(png_ptr, "Invalid cHRM white point specified");
  #if !defined(PNG_NO_CONSOLE_IO)
        fprintf(stderr,"white_x=%f, white_y=%f\n",white_x, white_y);
  #endif
        return;
     }
     itemp = (png_uint_32)(white_x * 100000.0 + 0.5);
     png_save_uint_32(buf, itemp);
     itemp = (png_uint_32)(white_y * 100000.0 + 0.5);
     png_save_uint_32(buf + 4, itemp);
  
     if (red_x < 0 || red_x > 0.8 || red_y < 0 || red_y > 0.8 ||
         red_x + red_y > 1.0)
     {
        png_warning(png_ptr, "Invalid cHRM red point specified");
        return;
     }
     itemp = (png_uint_32)(red_x * 100000.0 + 0.5);
     png_save_uint_32(buf + 8, itemp);
     itemp = (png_uint_32)(red_y * 100000.0 + 0.5);
     png_save_uint_32(buf + 12, itemp);
  
     if (green_x < 0 || green_x > 0.8 || green_y < 0 || green_y > 0.8 ||
         green_x + green_y > 1.0)
     {
        png_warning(png_ptr, "Invalid cHRM green point specified");
        return;
     }
     itemp = (png_uint_32)(green_x * 100000.0 + 0.5);
     png_save_uint_32(buf + 16, itemp);
     itemp = (png_uint_32)(green_y * 100000.0 + 0.5);
     png_save_uint_32(buf + 20, itemp);
  
     if (blue_x < 0 || blue_x > 0.8 || blue_y < 0 || blue_y > 0.8 ||
         blue_x + blue_y > 1.0)
     {
        png_warning(png_ptr, "Invalid cHRM blue point specified");
        return;
     }
     itemp = (png_uint_32)(blue_x * 100000.0 + 0.5);
     png_save_uint_32(buf + 24, itemp);
     itemp = (png_uint_32)(blue_y * 100000.0 + 0.5);
     png_save_uint_32(buf + 28, itemp);
  
     png_write_chunk(png_ptr, (png_bytep)png_cHRM, buf, (png_size_t)32);
  }
  #endif
  #ifdef PNG_FIXED_POINT_SUPPORTED
  void /* PRIVATE */
  png_write_cHRM_fixed(png_structp png_ptr, png_fixed_point white_x,
     png_fixed_point white_y, png_fixed_point red_x, png_fixed_point red_y,
     png_fixed_point green_x, png_fixed_point green_y, png_fixed_point blue_x,
     png_fixed_point blue_y)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_cHRM;
  #endif
     png_byte buf[32];
  
     png_debug(1, "in png_write_cHRM\n");
     /* each value is saved in 1/100,000ths */
     if (white_x > 80000L || white_y > 80000L || white_x + white_y > 100000L)
     {
        png_warning(png_ptr, "Invalid fixed cHRM white point specified");
  #if !defined(PNG_NO_CONSOLE_IO)
        fprintf(stderr,"white_x=%ld, white_y=%ld\n",white_x, white_y);
  #endif
        return;
     }
     png_save_uint_32(buf, (png_uint_32)white_x);
     png_save_uint_32(buf + 4, (png_uint_32)white_y);
  
     if (red_x > 80000L || red_y > 80000L || red_x + red_y > 100000L)
     {
        png_warning(png_ptr, "Invalid cHRM fixed red point specified");
        return;
     }
     png_save_uint_32(buf + 8, (png_uint_32)red_x);
     png_save_uint_32(buf + 12, (png_uint_32)red_y);
  
     if (green_x > 80000L || green_y > 80000L || green_x + green_y > 100000L)
     {
        png_warning(png_ptr, "Invalid fixed cHRM green point specified");
        return;
     }
     png_save_uint_32(buf + 16, (png_uint_32)green_x);
     png_save_uint_32(buf + 20, (png_uint_32)green_y);
  
     if (blue_x > 80000L || blue_y > 80000L || blue_x + blue_y > 100000L)
     {
        png_warning(png_ptr, "Invalid fixed cHRM blue point specified");
        return;
     }
     png_save_uint_32(buf + 24, (png_uint_32)blue_x);
     png_save_uint_32(buf + 28, (png_uint_32)blue_y);
  
     png_write_chunk(png_ptr, (png_bytep)png_cHRM, buf, (png_size_t)32);
  }
  #endif
  #endif
  
  #if defined(PNG_WRITE_tRNS_SUPPORTED)
  /* write the tRNS chunk */
  void /* PRIVATE */
  png_write_tRNS(png_structp png_ptr, png_bytep trans, png_color_16p tran,
     int num_trans, int color_type)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_tRNS;
  #endif
     png_byte buf[6];
  
     png_debug(1, "in png_write_tRNS\n");
     if (color_type == PNG_COLOR_TYPE_PALETTE)
     {
        if (num_trans <= 0 || num_trans > (int)png_ptr->num_palette)
        {
           png_warning(png_ptr,"Invalid number of transparent colors specified");
           return;
        }
        /* write the chunk out as it is */
        png_write_chunk(png_ptr, (png_bytep)png_tRNS, trans, (png_size_t)num_trans);
     }
     else if (color_type == PNG_COLOR_TYPE_GRAY)
     {
        /* one 16 bit value */
        if(tran->gray >= (1 << png_ptr->bit_depth))
        {
           png_warning(png_ptr,
             "Ignoring attempt to write tRNS chunk out-of-range for bit_depth");
           return;
        }
        png_save_uint_16(buf, tran->gray);
        png_write_chunk(png_ptr, (png_bytep)png_tRNS, buf, (png_size_t)2);
     }
     else if (color_type == PNG_COLOR_TYPE_RGB)
     {
        /* three 16 bit values */
        png_save_uint_16(buf, tran->red);
        png_save_uint_16(buf + 2, tran->green);
        png_save_uint_16(buf + 4, tran->blue);
        if(png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]))
           {
              png_warning(png_ptr,
                "Ignoring attempt to write 16-bit tRNS chunk when bit_depth is 8");
              return;
           }
        png_write_chunk(png_ptr, (png_bytep)png_tRNS, buf, (png_size_t)6);
     }
     else
     {
        png_warning(png_ptr, "Can't write tRNS with an alpha channel");
     }
  }
  #endif
  
  #if defined(PNG_WRITE_bKGD_SUPPORTED)
  /* write the background chunk */
  void /* PRIVATE */
  png_write_bKGD(png_structp png_ptr, png_color_16p back, int color_type)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_bKGD;
  #endif
     png_byte buf[6];
  
     png_debug(1, "in png_write_bKGD\n");
     if (color_type == PNG_COLOR_TYPE_PALETTE)
     {
        if (
  #if defined(PNG_MNG_FEATURES_SUPPORTED)
            (png_ptr->num_palette ||
            (!(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE))) &&
  #endif
           back->index > png_ptr->num_palette)
        {
           png_warning(png_ptr, "Invalid background palette index");
           return;
        }
        buf[0] = back->index;
        png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)1);
     }
     else if (color_type & PNG_COLOR_MASK_COLOR)
     {
        png_save_uint_16(buf, back->red);
        png_save_uint_16(buf + 2, back->green);
        png_save_uint_16(buf + 4, back->blue);
        if(png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]))
           {
              png_warning(png_ptr,
                "Ignoring attempt to write 16-bit bKGD chunk when bit_depth is 8");
              return;
           }
        png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)6);
     }
     else
     {
        if(back->gray >= (1 << png_ptr->bit_depth))
        {
           png_warning(png_ptr,
             "Ignoring attempt to write bKGD chunk out-of-range for bit_depth");
           return;
        }
        png_save_uint_16(buf, back->gray);
        png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)2);
     }
  }
  #endif
  
  #if defined(PNG_WRITE_hIST_SUPPORTED)
  /* write the histogram */
  void /* PRIVATE */
  png_write_hIST(png_structp png_ptr, png_uint_16p hist, int num_hist)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_hIST;
  #endif
     int i;
     png_byte buf[3];
  
     png_debug(1, "in png_write_hIST\n");
     if (num_hist > (int)png_ptr->num_palette)
     {
        png_debug2(3, "num_hist = %d, num_palette = %d\n", num_hist,
           png_ptr->num_palette);
        png_warning(png_ptr, "Invalid number of histogram entries specified");
        return;
     }
  
     png_write_chunk_start(png_ptr, (png_bytep)png_hIST, (png_uint_32)(num_hist * 2));
     for (i = 0; i < num_hist; i++)
     {
        png_save_uint_16(buf, hist[i]);
        png_write_chunk_data(png_ptr, buf, (png_size_t)2);
     }
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #if defined(PNG_WRITE_TEXT_SUPPORTED) || defined(PNG_WRITE_pCAL_SUPPORTED) || \
      defined(PNG_WRITE_iCCP_SUPPORTED) || defined(PNG_WRITE_sPLT_SUPPORTED)
  /* Check that the tEXt or zTXt keyword is valid per PNG 1.0 specification,
   * and if invalid, correct the keyword rather than discarding the entire
   * chunk.  The PNG 1.0 specification requires keywords 1-79 characters in
   * length, forbids leading or trailing whitespace, multiple internal spaces,
   * and the non-break space (0x80) from ISO 8859-1.  Returns keyword length.
   *
   * The new_key is allocated to hold the corrected keyword and must be freed
   * by the calling routine.  This avoids problems with trying to write to
   * static keywords without having to have duplicate copies of the strings.
   */
  png_size_t /* PRIVATE */
  png_check_keyword(png_structp png_ptr, png_charp key, png_charpp new_key)
  {
     png_size_t key_len;
     png_charp kp, dp;
     int kflag;
     int kwarn=0;
  
     png_debug(1, "in png_check_keyword\n");
     *new_key = NULL;
  
     if (key == NULL || (key_len = png_strlen(key)) == 0)
     {
        png_warning(png_ptr, "zero length keyword");
        return ((png_size_t)0);
     }
  
     png_debug1(2, "Keyword to be checked is '%s'\n", key);
  
     *new_key = (png_charp)png_malloc_warn(png_ptr, (png_uint_32)(key_len + 2));
     if (*new_key == NULL)
     {
        png_warning(png_ptr, "Out of memory while procesing keyword");
        return ((png_size_t)0);
     }
  
     /* Replace non-printing characters with a blank and print a warning */
     for (kp = key, dp = *new_key; *kp != '\0'; kp++, dp++)
     {
        if (*kp < 0x20 || (*kp > 0x7E && (png_byte)*kp < 0xA1))
        {
  #if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
           char msg[40];
  
           sprintf(msg, "invalid keyword character 0x%02X", *kp);
           png_warning(png_ptr, msg);
  #else
           png_warning(png_ptr, "invalid character in keyword");
  #endif
           *dp = ' ';
        }
        else
        {
           *dp = *kp;
        }
     }
     *dp = '\0';
  
     /* Remove any trailing white space. */
     kp = *new_key + key_len - 1;
     if (*kp == ' ')
     {
        png_warning(png_ptr, "trailing spaces removed from keyword");
  
        while (*kp == ' ')
        {
          *(kp--) = '\0';
          key_len--;
        }
     }
  
     /* Remove any leading white space. */
     kp = *new_key;
     if (*kp == ' ')
     {
        png_warning(png_ptr, "leading spaces removed from keyword");
  
        while (*kp == ' ')
        {
          kp++;
          key_len--;
        }
     }
  
     png_debug1(2, "Checking for multiple internal spaces in '%s'\n", kp);
  
     /* Remove multiple internal spaces. */
     for (kflag = 0, dp = *new_key; *kp != '\0'; kp++)
     {
        if (*kp == ' ' && kflag == 0)
        {
           *(dp++) = *kp;
           kflag = 1;
        }
        else if (*kp == ' ')
        {
           key_len--;
           kwarn=1;
        }
        else
        {
           *(dp++) = *kp;
           kflag = 0;
        }
     }
     *dp = '\0';
     if(kwarn)
        png_warning(png_ptr, "extra interior spaces removed from keyword");
  
     if (key_len == 0)
     {
        png_free(png_ptr, *new_key);
        *new_key=NULL;
        png_warning(png_ptr, "Zero length keyword");
     }
  
     if (key_len > 79)
     {
        png_warning(png_ptr, "keyword length must be 1 - 79 characters");
        new_key[79] = '\0';
        key_len = 79;
     }
  
     return (key_len);
  }
  #endif
  
  #if defined(PNG_WRITE_tEXt_SUPPORTED)
  /* write a tEXt chunk */
  void /* PRIVATE */
  png_write_tEXt(png_structp png_ptr, png_charp key, png_charp text,
     png_size_t text_len)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_tEXt;
  #endif
     png_size_t key_len;
     png_charp new_key;
  
     png_debug(1, "in png_write_tEXt\n");
     if (key == NULL || (key_len = png_check_keyword(png_ptr, key, &new_key))==0)
     {
        png_warning(png_ptr, "Empty keyword in tEXt chunk");
        return;
     }
  
     if (text == NULL || *text == '\0')
        text_len = 0;
     else
        text_len = png_strlen(text);
  
     /* make sure we include the 0 after the key */
     png_write_chunk_start(png_ptr, (png_bytep)png_tEXt, (png_uint_32)key_len+text_len+1);
     /*
      * We leave it to the application to meet PNG-1.0 requirements on the
      * contents of the text.  PNG-1.0 through PNG-1.2 discourage the use of
      * any non-Latin-1 characters except for NEWLINE.  ISO PNG will forbid them.
      * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
      */
     png_write_chunk_data(png_ptr, (png_bytep)new_key, key_len + 1);
     if (text_len)
        png_write_chunk_data(png_ptr, (png_bytep)text, text_len);
  
     png_write_chunk_end(png_ptr);
     png_free(png_ptr, new_key);
  }
  #endif
  
  #if defined(PNG_WRITE_zTXt_SUPPORTED)
  /* write a compressed text chunk */
  void /* PRIVATE */
  png_write_zTXt(png_structp png_ptr, png_charp key, png_charp text,
     png_size_t text_len, int compression)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_zTXt;
  #endif
     png_size_t key_len;
     char buf[1];
     png_charp new_key;
     compression_state comp;
  
     png_debug(1, "in png_write_zTXt\n");
  
     if (key == NULL || (key_len = png_check_keyword(png_ptr, key, &new_key))==0)
     {
        png_warning(png_ptr, "Empty keyword in zTXt chunk");
        return;
     }
  
     if (text == NULL || *text == '\0' || compression==PNG_TEXT_COMPRESSION_NONE)
     {
        png_write_tEXt(png_ptr, new_key, text, (png_size_t)0);
        png_free(png_ptr, new_key);
        return;
     }
  
     text_len = png_strlen(text);
  
     png_free(png_ptr, new_key);
  
     /* compute the compressed data; do it now for the length */
     text_len = png_text_compress(png_ptr, text, text_len, compression,
         &comp);
  
     /* write start of chunk */
     png_write_chunk_start(png_ptr, (png_bytep)png_zTXt, (png_uint_32)
        (key_len+text_len+2));
     /* write key */
     png_write_chunk_data(png_ptr, (png_bytep)key, key_len + 1);
     buf[0] = (png_byte)compression;
     /* write compression */
     png_write_chunk_data(png_ptr, (png_bytep)buf, (png_size_t)1);
     /* write the compressed data */
     png_write_compressed_data_out(png_ptr, &comp);
  
     /* close the chunk */
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #if defined(PNG_WRITE_iTXt_SUPPORTED)
  /* write an iTXt chunk */
  void /* PRIVATE */
  png_write_iTXt(png_structp png_ptr, int compression, png_charp key,
      png_charp lang, png_charp lang_key, png_charp text)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_iTXt;
  #endif
     png_size_t lang_len, key_len, lang_key_len, text_len;
     png_charp new_lang, new_key;
     png_byte cbuf[2];
     compression_state comp;
  
     png_debug(1, "in png_write_iTXt\n");
  
     if (key == NULL || (key_len = png_check_keyword(png_ptr, key, &new_key))==0)
     {
        png_warning(png_ptr, "Empty keyword in iTXt chunk");
        return;
     }
     if (lang == NULL || (lang_len = png_check_keyword(png_ptr, lang, &new_lang))==0)
     {
        png_warning(png_ptr, "Empty language field in iTXt chunk");
        new_lang = NULL;
        lang_len = 0;
     }
  
     if (lang_key == NULL)
       lang_key_len = 0;
     else
       lang_key_len = png_strlen(lang_key);
  
     if (text == NULL)
        text_len = 0;
     else
       text_len = png_strlen(text);
  
     /* compute the compressed data; do it now for the length */
     text_len = png_text_compress(png_ptr, text, text_len, compression-2,
        &comp);
  
  
     /* make sure we include the compression flag, the compression byte,
      * and the NULs after the key, lang, and lang_key parts */
  
     png_write_chunk_start(png_ptr, (png_bytep)png_iTXt,
            (png_uint_32)(
          5 /* comp byte, comp flag, terminators for key, lang and lang_key */
          + key_len
          + lang_len
          + lang_key_len
          + text_len));
  
     /*
      * We leave it to the application to meet PNG-1.0 requirements on the
      * contents of the text.  PNG-1.0 through PNG-1.2 discourage the use of
      * any non-Latin-1 characters except for NEWLINE.  ISO PNG will forbid them.
      * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
      */
     png_write_chunk_data(png_ptr, (png_bytep)new_key, key_len + 1);
  
     /* set the compression flag */
     if (compression == PNG_ITXT_COMPRESSION_NONE || \
         compression == PNG_TEXT_COMPRESSION_NONE)
         cbuf[0] = 0;
     else /* compression == PNG_ITXT_COMPRESSION_zTXt */
         cbuf[0] = 1;
     /* set the compression method */
     cbuf[1] = 0;
     png_write_chunk_data(png_ptr, cbuf, 2);
  
     cbuf[0] = 0;
     png_write_chunk_data(png_ptr, (new_lang ? (png_bytep)new_lang : cbuf), lang_len + 1);
     png_write_chunk_data(png_ptr, (lang_key ? (png_bytep)lang_key : cbuf), lang_key_len + 1);
     png_write_compressed_data_out(png_ptr, &comp);
  
     png_write_chunk_end(png_ptr);
     png_free(png_ptr, new_key);
     if (new_lang)
       png_free(png_ptr, new_lang);
  }
  #endif
  
  #if defined(PNG_WRITE_oFFs_SUPPORTED)
  /* write the oFFs chunk */
  void /* PRIVATE */
  png_write_oFFs(png_structp png_ptr, png_int_32 x_offset, png_int_32 y_offset,
     int unit_type)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_oFFs;
  #endif
     png_byte buf[9];
  
     png_debug(1, "in png_write_oFFs\n");
     if (unit_type >= PNG_OFFSET_LAST)
        png_warning(png_ptr, "Unrecognized unit type for oFFs chunk");
  
     png_save_int_32(buf, x_offset);
     png_save_int_32(buf + 4, y_offset);
     buf[8] = (png_byte)unit_type;
  
     png_write_chunk(png_ptr, (png_bytep)png_oFFs, buf, (png_size_t)9);
  }
  #endif
  
  #if defined(PNG_WRITE_pCAL_SUPPORTED)
  /* write the pCAL chunk (described in the PNG extensions document) */
  void /* PRIVATE */
  png_write_pCAL(png_structp png_ptr, png_charp purpose, png_int_32 X0,
     png_int_32 X1, int type, int nparams, png_charp units, png_charpp params)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_pCAL;
  #endif
     png_size_t purpose_len, units_len, total_len;
     png_uint_32p params_len;
     png_byte buf[10];
     png_charp new_purpose;
     int i;
  
     png_debug1(1, "in png_write_pCAL (%d parameters)\n", nparams);
     if (type >= PNG_EQUATION_LAST)
        png_warning(png_ptr, "Unrecognized equation type for pCAL chunk");
  
     purpose_len = png_check_keyword(png_ptr, purpose, &new_purpose) + 1;
     png_debug1(3, "pCAL purpose length = %d\n", (int)purpose_len);
     units_len = png_strlen(units) + (nparams == 0 ? 0 : 1);
     png_debug1(3, "pCAL units length = %d\n", (int)units_len);
     total_len = purpose_len + units_len + 10;
  
     params_len = (png_uint_32p)png_malloc(png_ptr, (png_uint_32)(nparams
        *png_sizeof(png_uint_32)));
  
     /* Find the length of each parameter, making sure we don't count the
        null terminator for the last parameter. */
     for (i = 0; i < nparams; i++)
     {
        params_len[i] = png_strlen(params[i]) + (i == nparams - 1 ? 0 : 1);
        png_debug2(3, "pCAL parameter %d length = %lu\n", i, params_len[i]);
        total_len += (png_size_t)params_len[i];
     }
  
     png_debug1(3, "pCAL total length = %d\n", (int)total_len);
     png_write_chunk_start(png_ptr, (png_bytep)png_pCAL, (png_uint_32)total_len);
     png_write_chunk_data(png_ptr, (png_bytep)new_purpose, purpose_len);
     png_save_int_32(buf, X0);
     png_save_int_32(buf + 4, X1);
     buf[8] = (png_byte)type;
     buf[9] = (png_byte)nparams;
     png_write_chunk_data(png_ptr, buf, (png_size_t)10);
     png_write_chunk_data(png_ptr, (png_bytep)units, (png_size_t)units_len);
  
     png_free(png_ptr, new_purpose);
  
     for (i = 0; i < nparams; i++)
     {
        png_write_chunk_data(png_ptr, (png_bytep)params[i],
           (png_size_t)params_len[i]);
     }
  
     png_free(png_ptr, params_len);
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #if defined(PNG_WRITE_sCAL_SUPPORTED)
  /* write the sCAL chunk */
  #if defined(PNG_FLOATING_POINT_SUPPORTED) && !defined(PNG_NO_STDIO)
  void /* PRIVATE */
  png_write_sCAL(png_structp png_ptr, int unit, double width,double height)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_sCAL;
  #endif
     png_size_t total_len;
     char wbuf[32], hbuf[32];
     png_byte bunit = unit;
  
     png_debug(1, "in png_write_sCAL\n");
  
  #if defined(_WIN32_WCE)
  /* sprintf() function is not supported on WindowsCE */
     {
        wchar_t wc_buf[32];
        swprintf(wc_buf, TEXT("%12.12e"), width);
        WideCharToMultiByte(CP_ACP, 0, wc_buf, -1, wbuf, 32, NULL, NULL);
        swprintf(wc_buf, TEXT("%12.12e"), height);
        WideCharToMultiByte(CP_ACP, 0, wc_buf, -1, hbuf, 32, NULL, NULL);
     }
  #else
     sprintf(wbuf, "%12.12e", width);
     sprintf(hbuf, "%12.12e", height);
  #endif
     total_len = 1 + png_strlen(wbuf)+1 + png_strlen(hbuf);
  
     png_debug1(3, "sCAL total length = %d\n", (int)total_len);
     png_write_chunk_start(png_ptr, (png_bytep)png_sCAL, (png_uint_32)total_len);
     png_write_chunk_data(png_ptr, (png_bytep)&bunit, 1);
     png_write_chunk_data(png_ptr, (png_bytep)wbuf, png_strlen(wbuf)+1);
     png_write_chunk_data(png_ptr, (png_bytep)hbuf, png_strlen(hbuf));
  
     png_write_chunk_end(png_ptr);
  }
  #else
  #ifdef PNG_FIXED_POINT_SUPPORTED
  void /* PRIVATE */
  png_write_sCAL_s(png_structp png_ptr, int unit, png_charp width,
     png_charp height)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_sCAL;
  #endif
     png_size_t total_len;
     char wbuf[32], hbuf[32];
     png_byte bunit = unit;
  
     png_debug(1, "in png_write_sCAL_s\n");
  
     png_strcpy(wbuf,(const char *)width);
     png_strcpy(hbuf,(const char *)height);
     total_len = 1 + png_strlen(wbuf)+1 + png_strlen(hbuf);
  
     png_debug1(3, "sCAL total length = %d\n", total_len);
     png_write_chunk_start(png_ptr, (png_bytep)png_sCAL, (png_uint_32)total_len);
     png_write_chunk_data(png_ptr, (png_bytep)&bunit, 1);
     png_write_chunk_data(png_ptr, (png_bytep)wbuf, png_strlen(wbuf)+1);
     png_write_chunk_data(png_ptr, (png_bytep)hbuf, png_strlen(hbuf));
  
     png_write_chunk_end(png_ptr);
  }
  #endif
  #endif
  #endif
  
  #if defined(PNG_WRITE_pHYs_SUPPORTED)
  /* write the pHYs chunk */
  void /* PRIVATE */
  png_write_pHYs(png_structp png_ptr, png_uint_32 x_pixels_per_unit,
     png_uint_32 y_pixels_per_unit,
     int unit_type)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_pHYs;
  #endif
     png_byte buf[9];
  
     png_debug(1, "in png_write_pHYs\n");
     if (unit_type >= PNG_RESOLUTION_LAST)
        png_warning(png_ptr, "Unrecognized unit type for pHYs chunk");
  
     png_save_uint_32(buf, x_pixels_per_unit);
     png_save_uint_32(buf + 4, y_pixels_per_unit);
     buf[8] = (png_byte)unit_type;
  
     png_write_chunk(png_ptr, (png_bytep)png_pHYs, buf, (png_size_t)9);
  }
  #endif
  
  #if defined(PNG_WRITE_tIME_SUPPORTED)
  /* Write the tIME chunk.  Use either png_convert_from_struct_tm()
   * or png_convert_from_time_t(), or fill in the structure yourself.
   */
  void /* PRIVATE */
  png_write_tIME(png_structp png_ptr, png_timep mod_time)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     PNG_tIME;
  #endif
     png_byte buf[7];
  
     png_debug(1, "in png_write_tIME\n");
     if (mod_time->month  > 12 || mod_time->month  < 1 ||
         mod_time->day    > 31 || mod_time->day    < 1 ||
         mod_time->hour   > 23 || mod_time->second > 60)
     {
        png_warning(png_ptr, "Invalid time specified for tIME chunk");
        return;
     }
  
     png_save_uint_16(buf, mod_time->year);
     buf[2] = mod_time->month;
     buf[3] = mod_time->day;
     buf[4] = mod_time->hour;
     buf[5] = mod_time->minute;
     buf[6] = mod_time->second;
  
     png_write_chunk(png_ptr, (png_bytep)png_tIME, buf, (png_size_t)7);
  }
  #endif
  
  /* initializes the row writing capability of libpng */
  void /* PRIVATE */
  png_write_start_row(png_structp png_ptr)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */
  
     /* start of interlace block */
     int png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
  
     /* offset to next interlace block */
     int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
  
     /* start of interlace block in the y direction */
     int png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
  
     /* offset to next interlace block in the y direction */
     int png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
  #endif
  
     png_size_t buf_size;
  
     png_debug(1, "in png_write_start_row\n");
     buf_size = (png_size_t)(PNG_ROWBYTES(
        png_ptr->usr_channels*png_ptr->usr_bit_depth,png_ptr->width)+1);
  
     /* set up row buffer */
     png_ptr->row_buf = (png_bytep)png_malloc(png_ptr, (png_uint_32)buf_size);
     png_ptr->row_buf[0] = PNG_FILTER_VALUE_NONE;
  
     /* set up filtering buffer, if using this filter */
     if (png_ptr->do_filter & PNG_FILTER_SUB)
     {
        png_ptr->sub_row = (png_bytep)png_malloc(png_ptr,
           (png_ptr->rowbytes + 1));
        png_ptr->sub_row[0] = PNG_FILTER_VALUE_SUB;
     }
  
     /* We only need to keep the previous row if we are using one of these. */
     if (png_ptr->do_filter & (PNG_FILTER_AVG | PNG_FILTER_UP | PNG_FILTER_PAETH))
     {
       /* set up previous row buffer */
        png_ptr->prev_row = (png_bytep)png_malloc(png_ptr, (png_uint_32)buf_size);
        png_memset(png_ptr->prev_row, 0, buf_size);
  
        if (png_ptr->do_filter & PNG_FILTER_UP)
        {
           png_ptr->up_row = (png_bytep )png_malloc(png_ptr,
              (png_ptr->rowbytes + 1));
           png_ptr->up_row[0] = PNG_FILTER_VALUE_UP;
        }
  
        if (png_ptr->do_filter & PNG_FILTER_AVG)
        {
           png_ptr->avg_row = (png_bytep)png_malloc(png_ptr,
              (png_ptr->rowbytes + 1));
           png_ptr->avg_row[0] = PNG_FILTER_VALUE_AVG;
        }
  
        if (png_ptr->do_filter & PNG_FILTER_PAETH)
        {
           png_ptr->paeth_row = (png_bytep )png_malloc(png_ptr,
              (png_ptr->rowbytes + 1));
           png_ptr->paeth_row[0] = PNG_FILTER_VALUE_PAETH;
        }
     }
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     /* if interlaced, we need to set up width and height of pass */
     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];
           png_ptr->usr_width = (png_ptr->width + png_pass_inc[0] - 1 -
              png_pass_start[0]) / png_pass_inc[0];
        }
        else
        {
           png_ptr->num_rows = png_ptr->height;
           png_ptr->usr_width = png_ptr->width;
        }
     }
     else
  #endif
     {
        png_ptr->num_rows = png_ptr->height;
        png_ptr->usr_width = png_ptr->width;
     }
     png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
     png_ptr->zstream.next_out = png_ptr->zbuf;
  }
  
  /* Internal use only.  Called when finished processing a row of data. */
  void /* PRIVATE */
  png_write_finish_row(png_structp png_ptr)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */
  
     /* start of interlace block */
     int png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
  
     /* offset to next interlace block */
     int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
  
     /* start of interlace block in the y direction */
     int png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
  
     /* offset to next interlace block in the y direction */
     int png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
  #endif
  
     int ret;
  
     png_debug(1, "in png_write_finish_row\n");
     /* next row */
     png_ptr->row_number++;
  
     /* see if we are done */
     if (png_ptr->row_number < png_ptr->num_rows)
        return;
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     /* if interlaced, go to next pass */
     if (png_ptr->interlaced)
     {
        png_ptr->row_number = 0;
        if (png_ptr->transformations & PNG_INTERLACE)
        {
           png_ptr->pass++;
        }
        else
        {
           /* loop until we find a non-zero width or height pass */
           do
           {
              png_ptr->pass++;
              if (png_ptr->pass >= 7)
                 break;
              png_ptr->usr_width = (png_ptr->width +
                 png_pass_inc[png_ptr->pass] - 1 -
                 png_pass_start[png_ptr->pass]) /
                 png_pass_inc[png_ptr->pass];
              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];
              if (png_ptr->transformations & PNG_INTERLACE)
                 break;
           } while (png_ptr->usr_width == 0 || png_ptr->num_rows == 0);
  
        }
  
        /* reset the row above the image for the next pass */
        if (png_ptr->pass < 7)
        {
           if (png_ptr->prev_row != NULL)
              png_memset(png_ptr->prev_row, 0,
                 (png_size_t)(PNG_ROWBYTES(png_ptr->usr_channels*
                 png_ptr->usr_bit_depth,png_ptr->width))+1);
           return;
        }
     }
  #endif
  
     /* if we get here, we've just written the last row, so we need
        to flush the compressor */
     do
     {
        /* tell the compressor we are done */
        ret = deflate(&png_ptr->zstream, Z_FINISH);
        /* check for an error */
        if (ret == Z_OK)
        {
           /* check to see if we need more room */
           if (!(png_ptr->zstream.avail_out))
           {
              png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
              png_ptr->zstream.next_out = png_ptr->zbuf;
              png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
           }
        }
        else if (ret != Z_STREAM_END)
        {
           if (png_ptr->zstream.msg != NULL)
              png_error(png_ptr, png_ptr->zstream.msg);
           else
              png_error(png_ptr, "zlib error");
        }
     } while (ret != Z_STREAM_END);
  
     /* write any extra space */
     if (png_ptr->zstream.avail_out < png_ptr->zbuf_size)
     {
        png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size -
           png_ptr->zstream.avail_out);
     }
  
     deflateReset(&png_ptr->zstream);
     png_ptr->zstream.data_type = Z_BINARY;
  }
  
  #if defined(PNG_WRITE_INTERLACING_SUPPORTED)
  /* Pick out the correct pixels for the interlace pass.
   * The basic idea here is to go through the row with a source
   * pointer and a destination pointer (sp and dp), and copy the
   * correct pixels for the pass.  As the row gets compacted,
   * sp will always be >= dp, so we should never overwrite anything.
   * See the default: case for the easiest code to understand.
   */
  void /* PRIVATE */
  png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
  {
  #ifdef PNG_USE_LOCAL_ARRAYS
     /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */
  
     /* start of interlace block */
     int png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
  
     /* offset to next interlace block */
     int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
  #endif
  
     png_debug(1, "in png_do_write_interlace\n");
     /* we don't have to do anything on the last pass (6) */
  #if defined(PNG_USELESS_TESTS_SUPPORTED)
     if (row != NULL && row_info != NULL && pass < 6)
  #else
     if (pass < 6)
  #endif
     {
        /* each pixel depth is handled separately */
        switch (row_info->pixel_depth)
        {
           case 1:
           {
              png_bytep sp;
              png_bytep dp;
              int shift;
              int d;
              int value;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              dp = row;
              d = 0;
              shift = 7;
              for (i = png_pass_start[pass]; i < row_width;
                 i += png_pass_inc[pass])
              {
                 sp = row + (png_size_t)(i >> 3);
                 value = (int)(*sp >> (7 - (int)(i & 0x07))) & 0x01;
                 d |= (value << shift);
  
                 if (shift == 0)
                 {
                    shift = 7;
                    *dp++ = (png_byte)d;
                    d = 0;
                 }
                 else
                    shift--;
  
              }
              if (shift != 7)
                 *dp = (png_byte)d;
              break;
           }
           case 2:
           {
              png_bytep sp;
              png_bytep dp;
              int shift;
              int d;
              int value;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              dp = row;
              shift = 6;
              d = 0;
              for (i = png_pass_start[pass]; i < row_width;
                 i += png_pass_inc[pass])
              {
                 sp = row + (png_size_t)(i >> 2);
                 value = (*sp >> ((3 - (int)(i & 0x03)) << 1)) & 0x03;
                 d |= (value << shift);
  
                 if (shift == 0)
                 {
                    shift = 6;
                    *dp++ = (png_byte)d;
                    d = 0;
                 }
                 else
                    shift -= 2;
              }
              if (shift != 6)
                     *dp = (png_byte)d;
              break;
           }
           case 4:
           {
              png_bytep sp;
              png_bytep dp;
              int shift;
              int d;
              int value;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              dp = row;
              shift = 4;
              d = 0;
              for (i = png_pass_start[pass]; i < row_width;
                 i += png_pass_inc[pass])
              {
                 sp = row + (png_size_t)(i >> 1);
                 value = (*sp >> ((1 - (int)(i & 0x01)) << 2)) & 0x0f;
                 d |= (value << shift);
  
                 if (shift == 0)
                 {
                    shift = 4;
                    *dp++ = (png_byte)d;
                    d = 0;
                 }
                 else
                    shift -= 4;
              }
              if (shift != 4)
                 *dp = (png_byte)d;
              break;
           }
           default:
           {
              png_bytep sp;
              png_bytep dp;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
              png_size_t pixel_bytes;
  
              /* start at the beginning */
              dp = row;
              /* find out how many bytes each pixel takes up */
              pixel_bytes = (row_info->pixel_depth >> 3);
              /* loop through the row, only looking at the pixels that
                 matter */
              for (i = png_pass_start[pass]; i < row_width;
                 i += png_pass_inc[pass])
              {
                 /* find out where the original pixel is */
                 sp = row + (png_size_t)i * pixel_bytes;
                 /* move the pixel */
                 if (dp != sp)
                    png_memcpy(dp, sp, pixel_bytes);
                 /* next pixel */
                 dp += pixel_bytes;
              }
              break;
           }
        }
        /* set new row width */
        row_info->width = (row_info->width +
           png_pass_inc[pass] - 1 -
           png_pass_start[pass]) /
           png_pass_inc[pass];
           row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
              row_info->width);
     }
  }
  #endif
  
  /* This filters the row, chooses which filter to use, if it has not already
   * been specified by the application, and then writes the row out with the
   * chosen filter.
   */
  #define PNG_MAXSUM (((png_uint_32)(-1)) >> 1)
  #define PNG_HISHIFT 10
  #define PNG_LOMASK ((png_uint_32)0xffffL)
  #define PNG_HIMASK ((png_uint_32)(~PNG_LOMASK >> PNG_HISHIFT))
  void /* PRIVATE */
  png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
  {
     png_bytep prev_row, best_row, row_buf;
     png_uint_32 mins, bpp;
     png_byte filter_to_do = png_ptr->do_filter;
     png_uint_32 row_bytes = row_info->rowbytes;
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
     int num_p_filters = (int)png_ptr->num_prev_filters;
  #endif
  
     png_debug(1, "in png_write_find_filter\n");
     /* find out how many bytes offset each pixel is */
     bpp = (row_info->pixel_depth + 7) >> 3;
  
     prev_row = png_ptr->prev_row;
     best_row = row_buf = png_ptr->row_buf;
     mins = PNG_MAXSUM;
  
     /* The prediction method we use is to find which method provides the
      * smallest value when summing the absolute values of the distances
      * from zero, using anything >= 128 as negative numbers.  This is known
      * as the "minimum sum of absolute differences" heuristic.  Other
      * heuristics are the "weighted minimum sum of absolute differences"
      * (experimental and can in theory improve compression), and the "zlib
      * predictive" method (not implemented yet), which does test compressions
      * of lines using different filter methods, and then chooses the
      * (series of) filter(s) that give minimum compressed data size (VERY
      * computationally expensive).
      *
      * GRR 980525:  consider also
      *   (1) minimum sum of absolute differences from running average (i.e.,
      *       keep running sum of non-absolute differences & count of bytes)
      *       [track dispersion, too?  restart average if dispersion too large?]
      *  (1b) minimum sum of absolute differences from sliding average, probably
      *       with window size <= deflate window (usually 32K)
      *   (2) minimum sum of squared differences from zero or running average
      *       (i.e., ~ root-mean-square approach)
      */
  
  
     /* We don't need to test the 'no filter' case if this is the only filter
      * that has been chosen, as it doesn't actually do anything to the data.
      */
     if ((filter_to_do & PNG_FILTER_NONE) &&
         filter_to_do != PNG_FILTER_NONE)
     {
        png_bytep rp;
        png_uint_32 sum = 0;
        png_uint_32 i;
        int v;
  
        for (i = 0, rp = row_buf + 1; i < row_bytes; i++, rp++)
        {
           v = *rp;
           sum += (v < 128) ? v : 256 - v;
        }
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
           png_uint_32 sumhi, sumlo;
           int j;
           sumlo = sum & PNG_LOMASK;
           sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK; /* Gives us some footroom */
  
           /* Reduce the sum if we match any of the previous rows */
           for (j = 0; j < num_p_filters; j++)
           {
              if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_NONE)
              {
                 sumlo = (sumlo * png_ptr->filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
                 sumhi = (sumhi * png_ptr->filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
              }
           }
  
           /* Factor in the cost of this filter (this is here for completeness,
            * but it makes no sense to have a "cost" for the NONE filter, as
            * it has the minimum possible computational cost - none).
            */
           sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_NONE]) >>
              PNG_COST_SHIFT;
           sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_NONE]) >>
              PNG_COST_SHIFT;
  
           if (sumhi > PNG_HIMASK)
              sum = PNG_MAXSUM;
           else
              sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
  #endif
        mins = sum;
     }
  
     /* sub filter */
     if (filter_to_do == PNG_FILTER_SUB)
     /* it's the only filter so no testing is needed */
     {
        png_bytep rp, lp, dp;
        png_uint_32 i;
        for (i = 0, rp = row_buf + 1, dp = png_ptr->sub_row + 1; i < bpp;
             i++, rp++, dp++)
        {
           *dp = *rp;
        }
        for (lp = row_buf + 1; i < row_bytes;
           i++, rp++, lp++, dp++)
        {
           *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
        }
        best_row = png_ptr->sub_row;
     }
  
     else if (filter_to_do & PNG_FILTER_SUB)
     {
        png_bytep rp, dp, lp;
        png_uint_32 sum = 0, lmins = mins;
        png_uint_32 i;
        int v;
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
        /* We temporarily increase the "minimum sum" by the factor we
         * would reduce the sum of this filter, so that we can do the
         * early exit comparison without scaling the sum each time.
         */
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
           int j;
           png_uint_32 lmhi, lmlo;
           lmlo = lmins & PNG_LOMASK;
           lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;
  
           for (j = 0; j < num_p_filters; j++)
           {
              if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_SUB)
              {
                 lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
                 lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
              }
           }
  
           lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
              PNG_COST_SHIFT;
           lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
              PNG_COST_SHIFT;
  
           if (lmhi > PNG_HIMASK)
              lmins = PNG_MAXSUM;
           else
              lmins = (lmhi << PNG_HISHIFT) + lmlo;
        }
  #endif
  
        for (i = 0, rp = row_buf + 1, dp = png_ptr->sub_row + 1; i < bpp;
             i++, rp++, dp++)
        {
           v = *dp = *rp;
  
           sum += (v < 128) ? v : 256 - v;
        }
        for (lp = row_buf + 1; i < row_bytes;
           i++, rp++, lp++, dp++)
        {
           v = *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
  
           sum += (v < 128) ? v : 256 - v;
  
           if (sum > lmins)  /* We are already worse, don't continue. */
              break;
        }
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
           int j;
           png_uint_32 sumhi, sumlo;
           sumlo = sum & PNG_LOMASK;
           sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK;
  
           for (j = 0; j < num_p_filters; j++)
           {
              if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_SUB)
              {
                 sumlo = (sumlo * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
                 sumhi = (sumhi * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
              }
           }
  
           sumlo = (sumlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
              PNG_COST_SHIFT;
           sumhi = (sumhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
              PNG_COST_SHIFT;
  
           if (sumhi > PNG_HIMASK)
              sum = PNG_MAXSUM;
           else
              sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
  #endif
  
        if (sum < mins)
        {
           mins = sum;
           best_row = png_ptr->sub_row;
        }
     }
  
     /* up filter */
     if (filter_to_do == PNG_FILTER_UP)
     {
        png_bytep rp, dp, pp;
        png_uint_32 i;
  
        for (i = 0, rp = row_buf + 1, dp = png_ptr->up_row + 1,
             pp = prev_row + 1; i < row_bytes;
             i++, rp++, pp++, dp++)
        {
           *dp = (png_byte)(((int)*rp - (int)*pp) & 0xff);
        }
        best_row = png_ptr->up_row;
     }
  
     else if (filter_to_do & PNG_FILTER_UP)
     {
        png_bytep rp, dp, pp;
        png_uint_32 sum = 0, lmins = mins;
        png_uint_32 i;
        int v;
  
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
           int j;
           png_uint_32 lmhi, lmlo;
           lmlo = lmins & PNG_LOMASK;
           lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;
  
           for (j = 0; j < num_p_filters; j++)
           {
              if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_UP)
              {
                 lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
                 lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
              }
           }
  
           lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_UP]) >>
              PNG_COST_SHIFT;
           lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_UP]) >>
              PNG_COST_SHIFT;
  
           if (lmhi > PNG_HIMASK)
              lmins = PNG_MAXSUM;
           else
              lmins = (lmhi << PNG_HISHIFT) + lmlo;
        }
  #endif
  
        for (i = 0, rp = row_buf + 1, dp = png_ptr->up_row + 1,
             pp = prev_row + 1; i < row_bytes; i++)
        {
           v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
  
           sum += (v < 128) ? v : 256 - v;
  
           if (sum > lmins)  /* We are already worse, don't continue. */
              break;
        }
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
           int j;
           png_uint_32 sumhi, sumlo;
           sumlo = sum & PNG_LOMASK;
           sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK;
  
           for (j = 0; j < num_p_filters; j++)
           {
              if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_UP)
              {
                 sumlo = (sumlo * png_ptr->filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
                 sumhi = (sumhi * png_ptr->filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
              }
           }
  
           sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_UP]) >>
              PNG_COST_SHIFT;
           sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_UP]) >>
              PNG_COST_SHIFT;
  
           if (sumhi > PNG_HIMASK)
              sum = PNG_MAXSUM;
           else
              sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
  #endif
  
        if (sum < mins)
        {
           mins = sum;
           best_row = png_ptr->up_row;
        }
     }
  
     /* avg filter */
     if (filter_to_do == PNG_FILTER_AVG)
     {
        png_bytep rp, dp, pp, lp;
        png_uint_32 i;
        for (i = 0, rp = row_buf + 1, dp = png_ptr->avg_row + 1,
             pp = prev_row + 1; i < bpp; i++)
        {
           *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
        }
        for (lp = row_buf + 1; i < row_bytes; i++)
        {
           *dp++ = (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2))
                   & 0xff);
        }
        best_row = png_ptr->avg_row;
     }
  
     else if (filter_to_do & PNG_FILTER_AVG)
     {
        png_bytep rp, dp, pp, lp;
        png_uint_32 sum = 0, lmins = mins;
        png_uint_32 i;
        int v;
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
           int j;
           png_uint_32 lmhi, lmlo;
           lmlo = lmins & PNG_LOMASK;
           lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;
  
           for (j = 0; j < num_p_filters; j++)
           {
              if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_AVG)
              {
                 lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
                 lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
              }
           }
  
           lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_AVG]) >>
              PNG_COST_SHIFT;
           lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_AVG]) >>
              PNG_COST_SHIFT;
  
           if (lmhi > PNG_HIMASK)
              lmins = PNG_MAXSUM;
           else
              lmins = (lmhi << PNG_HISHIFT) + lmlo;
        }
  #endif
  
        for (i = 0, rp = row_buf + 1, dp = png_ptr->avg_row + 1,
             pp = prev_row + 1; i < bpp; i++)
        {
           v = *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
  
           sum += (v < 128) ? v : 256 - v;
        }
        for (lp = row_buf + 1; i < row_bytes; i++)
        {
           v = *dp++ =
            (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2)) & 0xff);
  
           sum += (v < 128) ? v : 256 - v;
  
           if (sum > lmins)  /* We are already worse, don't continue. */
              break;
        }
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
           int j;
           png_uint_32 sumhi, sumlo;
           sumlo = sum & PNG_LOMASK;
           sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK;
  
           for (j = 0; j < num_p_filters; j++)
           {
              if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_NONE)
              {
                 sumlo = (sumlo * png_ptr->filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
                 sumhi = (sumhi * png_ptr->filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
              }
           }
  
           sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_AVG]) >>
              PNG_COST_SHIFT;
           sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_AVG]) >>
              PNG_COST_SHIFT;
  
           if (sumhi > PNG_HIMASK)
              sum = PNG_MAXSUM;
           else
              sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
  #endif
  
        if (sum < mins)
        {
           mins = sum;
           best_row = png_ptr->avg_row;
        }
     }
  
     /* Paeth filter */
     if (filter_to_do == PNG_FILTER_PAETH)
     {
        png_bytep rp, dp, pp, cp, lp;
        png_uint_32 i;
        for (i = 0, rp = row_buf + 1, dp = png_ptr->paeth_row + 1,
             pp = prev_row + 1; i < bpp; i++)
        {
           *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
        }
  
        for (lp = row_buf + 1, cp = prev_row + 1; i < row_bytes; i++)
        {
           int a, b, c, pa, pb, pc, p;
  
           b = *pp++;
           c = *cp++;
           a = *lp++;
  
           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
  
           p = (pa <= pb && pa <=pc) ? a : (pb <= pc) ? b : c;
  
           *dp++ = (png_byte)(((int)*rp++ - p) & 0xff);
        }
        best_row = png_ptr->paeth_row;
     }
  
     else if (filter_to_do & PNG_FILTER_PAETH)
     {
        png_bytep rp, dp, pp, cp, lp;
        png_uint_32 sum = 0, lmins = mins;
        png_uint_32 i;
        int v;
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
           int j;
           png_uint_32 lmhi, lmlo;
           lmlo = lmins & PNG_LOMASK;
           lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;
  
           for (j = 0; j < num_p_filters; j++)
           {
              if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_PAETH)
              {
                 lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
                 lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
              }
           }
  
           lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_PAETH]) >>
              PNG_COST_SHIFT;
           lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_PAETH]) >>
              PNG_COST_SHIFT;
  
           if (lmhi > PNG_HIMASK)
              lmins = PNG_MAXSUM;
           else
              lmins = (lmhi << PNG_HISHIFT) + lmlo;
        }
  #endif
  
        for (i = 0, rp = row_buf + 1, dp = png_ptr->paeth_row + 1,
             pp = prev_row + 1; i < bpp; i++)
        {
           v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
  
           sum += (v < 128) ? v : 256 - v;
        }
  
        for (lp = row_buf + 1, cp = prev_row + 1; i < row_bytes; i++)
        {
           int a, b, c, pa, pb, pc, p;
  
           b = *pp++;
           c = *cp++;
           a = *lp++;
  
  #ifndef PNG_SLOW_PAETH
           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
           p = (pa <= pb && pa <=pc) ? a : (pb <= pc) ? b : c;
  #else /* PNG_SLOW_PAETH */
           p = a + b - c;
           pa = abs(p - a);
           pb = abs(p - b);
           pc = abs(p - c);
           if (pa <= pb && pa <= pc)
              p = a;
           else if (pb <= pc)
              p = b;
           else
              p = c;
  #endif /* PNG_SLOW_PAETH */
  
           v = *dp++ = (png_byte)(((int)*rp++ - p) & 0xff);
  
           sum += (v < 128) ? v : 256 - v;
  
           if (sum > lmins)  /* We are already worse, don't continue. */
              break;
        }
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
        if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
        {
           int j;
           png_uint_32 sumhi, sumlo;
           sumlo = sum & PNG_LOMASK;
           sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK;
  
           for (j = 0; j < num_p_filters; j++)
           {
              if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_PAETH)
              {
                 sumlo = (sumlo * png_ptr->filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
                 sumhi = (sumhi * png_ptr->filter_weights[j]) >>
                    PNG_WEIGHT_SHIFT;
              }
           }
  
           sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_PAETH]) >>
              PNG_COST_SHIFT;
           sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_PAETH]) >>
              PNG_COST_SHIFT;
  
           if (sumhi > PNG_HIMASK)
              sum = PNG_MAXSUM;
           else
              sum = (sumhi << PNG_HISHIFT) + sumlo;
        }
  #endif
  
        if (sum < mins)
        {
           best_row = png_ptr->paeth_row;
        }
     }
  
     /* Do the actual writing of the filtered row data from the chosen filter. */
  
     png_write_filtered_row(png_ptr, best_row);
  
  #if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
     /* Save the type of filter we picked this time for future calculations */
     if (png_ptr->num_prev_filters > 0)
     {
        int j;
        for (j = 1; j < num_p_filters; j++)
        {
           png_ptr->prev_filters[j] = png_ptr->prev_filters[j - 1];
        }
        png_ptr->prev_filters[j] = best_row[0];
     }
  #endif
  }
  
  
  /* Do the actual writing of a previously filtered row. */
  void /* PRIVATE */
  png_write_filtered_row(png_structp png_ptr, png_bytep filtered_row)
  {
     png_debug(1, "in png_write_filtered_row\n");
     png_debug1(2, "filter = %d\n", filtered_row[0]);
     /* set up the zlib input buffer */
  
     png_ptr->zstream.next_in = filtered_row;
     png_ptr->zstream.avail_in = (uInt)png_ptr->row_info.rowbytes + 1;
     /* repeat until we have compressed all the data */
     do
     {
        int ret; /* return of zlib */
  
        /* compress the data */
        ret = deflate(&png_ptr->zstream, Z_NO_FLUSH);
        /* check for compression errors */
        if (ret != Z_OK)
        {
           if (png_ptr->zstream.msg != NULL)
              png_error(png_ptr, png_ptr->zstream.msg);
           else
              png_error(png_ptr, "zlib error");
        }
  
        /* see if it is time to write another IDAT */
        if (!(png_ptr->zstream.avail_out))
        {
           /* write the IDAT and reset the zlib output buffer */
           png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
           png_ptr->zstream.next_out = png_ptr->zbuf;
           png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
        }
     /* repeat until all data has been compressed */
     } while (png_ptr->zstream.avail_in);
  
     /* swap the current and previous rows */
     if (png_ptr->prev_row != NULL)
     {
        png_bytep tptr;
  
        tptr = png_ptr->prev_row;
        png_ptr->prev_row = png_ptr->row_buf;
        png_ptr->row_buf = tptr;
     }
  
     /* finish row - updates counters and flushes zlib if last row */
     png_write_finish_row(png_ptr);
  
  #if defined(PNG_WRITE_FLUSH_SUPPORTED)
     png_ptr->flush_rows++;
  
     if (png_ptr->flush_dist > 0 &&
         png_ptr->flush_rows >= png_ptr->flush_dist)
     {
        png_write_flush(png_ptr);
     }
  #endif
  }
  #endif /* PNG_WRITE_SUPPORTED */
  