text: 
  /* pngread.c - read a PNG file
   *
   * Copyright (c) 2018-2019 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 an application calls directly to
   * read a PNG file or stream.
   */
  
  #include "pngpriv.h"
  
  #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) && defined(PNG_STDIO_SUPPORTED)
  #  include <errno.h>
  
  #endif
  
  #ifdef PNG_READ_SUPPORTED
  
  /* Create a PNG structure for reading, and allocate any memory needed. */
  PNG_FUNCTION(png_structp, PNGAPI
      png_create_read_struct, (png_const_charp user_png_ver, png_voidp error_ptr,
      png_error_ptr error_fn, png_error_ptr warn_fn), PNG_ALLOCATED) {
  #ifndef PNG_USER_MEM_SUPPORTED
                                                                                                                            png_structp png_ptr = png_create_png_struct(user_png_ver, error_ptr,
          error_fn, warn_fn, NULL, NULL, NULL);
  #else
    return png_create_read_struct_2 (user_png_ver, error_ptr, error_fn,
                                     warn_fn, NULL, NULL, NULL);
  }
  
  /* Alternate create PNG structure for reading, and allocate any memory
   * needed.
   */
  PNG_FUNCTION(png_structp, PNGAPI
      png_create_read_struct_2, (png_const_charp user_png_ver, png_voidp error_ptr,
      png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr,
      png_malloc_ptr malloc_fn, png_free_ptr free_fn), PNG_ALLOCATED) {
    png_structp png_ptr = png_create_png_struct (user_png_ver, error_ptr,
                                                 error_fn, warn_fn, mem_ptr, malloc_fn, free_fn);
  #endif /* USER_MEM */
  
    if (png_ptr != NULL) {
      png_ptr->mode = PNG_IS_READ_STRUCT;
  
      /* Added in libpng-1.6.0; this can be used to detect a read structure if
         * required (it will be zero in a write structure.)
         */
  #     ifdef PNG_SEQUENTIAL_READ_SUPPORTED
      png_ptr->IDAT_read_size = PNG_IDAT_READ_SIZE;
  #     endif
  
  #     ifdef PNG_BENIGN_READ_ERRORS_SUPPORTED
      png_ptr->flags |= PNG_FLAG_BENIGN_ERRORS_WARN;
  
      /* In stable builds only warn if an application error can be completely
            * handled.
            */
  #        if PNG_RELEASE_BUILD
      png_ptr->flags |= PNG_FLAG_APP_WARNINGS_WARN;
  #        endif
  #     endif
  
      /* TODO: delay this, it can be done in png_init_io (if the app doesn't
         * do it itself) avoiding setting the default function if it is not
         * required.
         */
      png_set_read_fn (png_ptr, NULL, NULL);
    }
  
    return png_ptr;
  }
  
  #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
  
  /* Read the information before the actual image data.  This has been
   * changed in v0.90 to allow reading a file that already has the magic
   * bytes read from the stream.  You can tell libpng how many bytes have
   * been read from the beginning of the stream (up to the maximum of 8)
   * via png_set_sig_bytes(), and we will only check the remaining bytes
   * here.  The application can then have access to the signature bytes we
   * read if it is determined that this isn't a valid PNG file.
   */
  void PNGAPI
  png_read_info (png_structrp png_ptr, png_inforp info_ptr) {
  #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
    int keep;
  #endif
  
    png_debug(1, "in png_read_info");
  
    if (png_ptr == NULL || info_ptr == NULL)
      return;
  
    /* Read and check the PNG file signature. */
    png_read_sig (png_ptr, info_ptr);
  
    for (;;) {
      png_uint_32 length = png_read_chunk_header (png_ptr);
      png_uint_32 chunk_name = png_ptr->chunk_name;
  
      /* IDAT logic needs to happen here to simplify getting the two flags
         * right.
         */
      if (chunk_name == png_IDAT) {
        if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
          png_chunk_error (png_ptr, "Missing IHDR before IDAT");
  
        else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
                 (png_ptr->mode & PNG_HAVE_PLTE) == 0)
          png_chunk_error (png_ptr, "Missing PLTE before IDAT");
  
        else if ((png_ptr->mode & PNG_AFTER_IDAT) != 0)
          png_chunk_benign_error (png_ptr, "Too many IDATs found");
  
        png_ptr->mode |= PNG_HAVE_IDAT;
      }
  
      else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0) {
        png_ptr->mode |= PNG_HAVE_CHUNK_AFTER_IDAT;
        png_ptr->mode |= PNG_AFTER_IDAT;
      }
  
      /* This should be a binary subdivision search or a hash for
         * matching the chunk name rather than a linear search.
         */
      if (chunk_name == png_IHDR)
        png_handle_IHDR (png_ptr, info_ptr, length);
  
      else if (chunk_name == png_IEND)
        png_handle_IEND (png_ptr, info_ptr, length);
  
  #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
      else if ((keep = png_chunk_unknown_handling (png_ptr, chunk_name)) != 0) {
        png_handle_unknown (png_ptr, info_ptr, length, keep);
  
        if (chunk_name == png_PLTE)
          png_ptr->mode |= PNG_HAVE_PLTE;
  
        else if (chunk_name == png_IDAT) {
          png_ptr->idat_size = 0; /* It has been consumed */
          break;
        }
      }
  #endif
      else if (chunk_name == png_PLTE)
        png_handle_PLTE (png_ptr, info_ptr, length);
  
      else if (chunk_name == png_IDAT) {
        png_ptr->idat_size = length;
        break;
      }
  
  #ifdef PNG_READ_bKGD_SUPPORTED
      else if (chunk_name == png_bKGD)
        png_handle_bKGD (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_cHRM_SUPPORTED
      else if (chunk_name == png_cHRM)
        png_handle_cHRM (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_eXIf_SUPPORTED
      else if (chunk_name == png_eXIf)
        png_handle_eXIf (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_gAMA_SUPPORTED
      else if (chunk_name == png_gAMA)
        png_handle_gAMA (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_hIST_SUPPORTED
      else if (chunk_name == png_hIST)
        png_handle_hIST (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_oFFs_SUPPORTED
      else if (chunk_name == png_oFFs)
        png_handle_oFFs (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_pCAL_SUPPORTED
      else if (chunk_name == png_pCAL)
        png_handle_pCAL (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_sCAL_SUPPORTED
      else if (chunk_name == png_sCAL)
        png_handle_sCAL (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_pHYs_SUPPORTED
      else if (chunk_name == png_pHYs)
        png_handle_pHYs (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_sBIT_SUPPORTED
      else if (chunk_name == png_sBIT)
        png_handle_sBIT (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_sRGB_SUPPORTED
      else if (chunk_name == png_sRGB)
        png_handle_sRGB (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_iCCP_SUPPORTED
      else if (chunk_name == png_iCCP)
        png_handle_iCCP (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_sPLT_SUPPORTED
      else if (chunk_name == png_sPLT)
        png_handle_sPLT (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_tEXt_SUPPORTED
      else if (chunk_name == png_tEXt)
        png_handle_tEXt (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_tIME_SUPPORTED
      else if (chunk_name == png_tIME)
        png_handle_tIME (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_tRNS_SUPPORTED
      else if (chunk_name == png_tRNS)
        png_handle_tRNS (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_zTXt_SUPPORTED
      else if (chunk_name == png_zTXt)
        png_handle_zTXt (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_iTXt_SUPPORTED
      else if (chunk_name == png_iTXt)
        png_handle_iTXt (png_ptr, info_ptr, length);
  #endif
  
      else
        png_handle_unknown (png_ptr, info_ptr, length,
                            PNG_HANDLE_CHUNK_AS_DEFAULT);
    }
  }
  
  #endif /* SEQUENTIAL_READ */
  
  /* Optional call to update the users info_ptr structure */
  void PNGAPI
  png_read_update_info (png_structrp png_ptr, png_inforp info_ptr) {
    png_debug(1, "in png_read_update_info");
  
    if (png_ptr != NULL) {
      if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0) {
        png_read_start_row (png_ptr);
  
  #        ifdef PNG_READ_TRANSFORMS_SUPPORTED
        png_read_transform_info (png_ptr, info_ptr);
  #        else
        PNG_UNUSED(info_ptr)
  #        endif
      }
  
        /* New in 1.6.0 this avoids the bug of doing the initializations twice */
      else
        png_app_error (png_ptr,
                       "png_read_update_info/png_start_read_image: duplicate call");
    }
  }
  
  #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
  
  /* Initialize palette, background, etc, after transformations
   * are set, but before any reading takes place.  This allows
   * the user to obtain a gamma-corrected palette, for example.
   * If the user doesn't call this, we will do it ourselves.
   */
  void PNGAPI
  png_start_read_image (png_structrp png_ptr) {
    png_debug(1, "in png_start_read_image");
  
    if (png_ptr != NULL) {
      if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)
        png_read_start_row (png_ptr);
  
        /* New in 1.6.0 this avoids the bug of doing the initializations twice */
      else
        png_app_error (png_ptr,
                       "png_start_read_image/png_read_update_info: duplicate call");
    }
  }
  
  #endif /* SEQUENTIAL_READ */
  
  #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
  #ifdef PNG_MNG_FEATURES_SUPPORTED
  
  /* Undoes intrapixel differencing,
   * NOTE: this is apparently only supported in the 'sequential' reader.
   */
  static void
  png_do_read_intrapixel (png_row_infop row_info, png_bytep row) {
    png_debug(1, "in png_do_read_intrapixel");
  
    if (
        (row_info->color_type & PNG_COLOR_MASK_COLOR) != 0) {
      int bytes_per_pixel;
      png_uint_32 row_width = row_info->width;
  
      if (row_info->bit_depth == 8) {
        png_bytep rp;
        png_uint_32 i;
  
        if (row_info->color_type == PNG_COLOR_TYPE_RGB)
          bytes_per_pixel = 3;
  
        else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
          bytes_per_pixel = 4;
  
        else
          return;
  
        for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel) {
          *(rp) = (png_byte) ((256 + *rp + *(rp + 1)) & 0xff);
          *(rp + 2) = (png_byte) ((256 + *(rp + 2) + *(rp + 1)) & 0xff);
        }
      }
      else if (row_info->bit_depth == 16) {
        png_bytep rp;
        png_uint_32 i;
  
        if (row_info->color_type == PNG_COLOR_TYPE_RGB)
          bytes_per_pixel = 6;
  
        else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
          bytes_per_pixel = 8;
  
        else
          return;
  
        for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel) {
          png_uint_32 s0 = (png_uint_32) (*(rp) << 8) | *(rp + 1);
          png_uint_32 s1 = (png_uint_32) (*(rp + 2) << 8) | *(rp + 3);
          png_uint_32 s2 = (png_uint_32) (*(rp + 4) << 8) | *(rp + 5);
          png_uint_32 red = (s0 + s1 + 65536) & 0xffff;
          png_uint_32 blue = (s2 + s1 + 65536) & 0xffff;
          *(rp) = (png_byte) ((red >> 8) & 0xff);
          *(rp + 1) = (png_byte) (red & 0xff);
          *(rp + 4) = (png_byte) ((blue >> 8) & 0xff);
          *(rp + 5) = (png_byte) (blue & 0xff);
        }
      }
    }
  }
  
  #endif /* MNG_FEATURES */
  
  void PNGAPI
  png_read_row (png_structrp png_ptr, png_bytep row, png_bytep dsp_row) {
    png_row_info row_info;
  
    if (png_ptr == NULL)
      return;
  
    png_debug2(1, "in png_read_row (row %lu, pass %d)",
               (unsigned long) png_ptr->row_number, png_ptr->pass);
  
    /* png_read_start_row sets the information (in particular iwidth) for this
      * interlace pass.
      */
    if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)
      png_read_start_row (png_ptr);
  
    /* 1.5.6: row_info moved out of png_struct to a local here. */
    row_info.width = png_ptr->iwidth; /* NOTE: width of current interlaced row */
    row_info.color_type = png_ptr->color_type;
    row_info.bit_depth = png_ptr->bit_depth;
    row_info.channels = png_ptr->channels;
    row_info.pixel_depth = png_ptr->pixel_depth;
    row_info.rowbytes = PNG_ROWBYTES(row_info.pixel_depth, row_info.width);
  
  #ifdef PNG_WARNINGS_SUPPORTED
    if (png_ptr->row_number == 0 && png_ptr->pass == 0) {
      /* Check for transforms that have been set but were defined out */
  #if defined(PNG_WRITE_INVERT_SUPPORTED) && !defined(PNG_READ_INVERT_SUPPORTED)
                                                                                                                              if ((png_ptr->transformations & PNG_INVERT_MONO) != 0)
        png_warning(png_ptr, "PNG_READ_INVERT_SUPPORTED is not defined");
  #endif
  
  #if defined(PNG_WRITE_FILLER_SUPPORTED) && !defined(PNG_READ_FILLER_SUPPORTED)
                                                                                                                              if ((png_ptr->transformations & PNG_FILLER) != 0)
        png_warning(png_ptr, "PNG_READ_FILLER_SUPPORTED is not defined");
  #endif
  
  #if defined(PNG_WRITE_PACKSWAP_SUPPORTED) && \
      !defined(PNG_READ_PACKSWAP_SUPPORTED)
                                                                                                                              if ((png_ptr->transformations & PNG_PACKSWAP) != 0)
        png_warning(png_ptr, "PNG_READ_PACKSWAP_SUPPORTED is not defined");
  #endif
  
  #if defined(PNG_WRITE_PACK_SUPPORTED) && !defined(PNG_READ_PACK_SUPPORTED)
                                                                                                                              if ((png_ptr->transformations & PNG_PACK) != 0)
        png_warning(png_ptr, "PNG_READ_PACK_SUPPORTED is not defined");
  #endif
  
  #if defined(PNG_WRITE_SHIFT_SUPPORTED) && !defined(PNG_READ_SHIFT_SUPPORTED)
                                                                                                                              if ((png_ptr->transformations & PNG_SHIFT) != 0)
        png_warning(png_ptr, "PNG_READ_SHIFT_SUPPORTED is not defined");
  #endif
  
  #if defined(PNG_WRITE_BGR_SUPPORTED) && !defined(PNG_READ_BGR_SUPPORTED)
                                                                                                                              if ((png_ptr->transformations & PNG_BGR) != 0)
        png_warning(png_ptr, "PNG_READ_BGR_SUPPORTED is not defined");
  #endif
  
  #if defined(PNG_WRITE_SWAP_SUPPORTED) && !defined(PNG_READ_SWAP_SUPPORTED)
                                                                                                                              if ((png_ptr->transformations & PNG_SWAP_BYTES) != 0)
        png_warning(png_ptr, "PNG_READ_SWAP_SUPPORTED is not defined");
  #endif
    }
  #endif /* WARNINGS */
  
  #ifdef PNG_READ_INTERLACING_SUPPORTED
    /* If interlaced and we do not need a new row, combine row and return.
      * Notice that the pixels we have from previous rows have been transformed
      * already; we can only combine like with like (transformed or
      * untransformed) and, because of the libpng API for interlaced images, this
      * means we must transform before de-interlacing.
      */
    if (png_ptr->interlaced != 0 &&
        (png_ptr->transformations & PNG_INTERLACE) != 0) {
      switch (png_ptr->pass) {
        case 0:
          if (png_ptr->row_number & 0x07) {
            if (dsp_row != NULL)
              png_combine_row (png_ptr, dsp_row, 1/*display*/);
            png_read_finish_row (png_ptr);
            return;
          }
          break;
  
        case 1:
          if ((png_ptr->row_number & 0x07) || png_ptr->width < 5) {
            if (dsp_row != NULL)
              png_combine_row (png_ptr, dsp_row, 1/*display*/);
  
            png_read_finish_row (png_ptr);
            return;
          }
          break;
  
        case 2:
          if ((png_ptr->row_number & 0x07) != 4) {
            if (dsp_row != NULL && (png_ptr->row_number & 4))
              png_combine_row (png_ptr, dsp_row, 1/*display*/);
  
            png_read_finish_row (png_ptr);
            return;
          }
          break;
  
        case 3:
          if ((png_ptr->row_number & 3) || png_ptr->width < 3) {
            if (dsp_row != NULL)
              png_combine_row (png_ptr, dsp_row, 1/*display*/);
  
            png_read_finish_row (png_ptr);
            return;
          }
          break;
  
        case 4:
          if ((png_ptr->row_number & 3) != 2) {
            if (dsp_row != NULL && (png_ptr->row_number & 2))
              png_combine_row (png_ptr, dsp_row, 1/*display*/);
  
            png_read_finish_row (png_ptr);
            return;
          }
          break;
  
        case 5:
          if ((png_ptr->row_number & 1) || png_ptr->width < 2) {
            if (dsp_row != NULL)
              png_combine_row (png_ptr, dsp_row, 1/*display*/);
  
            png_read_finish_row (png_ptr);
            return;
          }
          break;
  
        default:
        case 6:
          if ((png_ptr->row_number & 1) == 0) {
            png_read_finish_row (png_ptr);
            return;
          }
          break;
      }
    }
  #endif
  
    if ((png_ptr->mode & PNG_HAVE_IDAT) == 0)
      png_error (png_ptr, "Invalid attempt to read row data");
  
    /* Fill the row with IDAT data: */
    png_ptr->row_buf[0] = 255; /* to force error if no data was found */
    png_read_IDAT_data (png_ptr, png_ptr->row_buf, row_info.rowbytes + 1);
  
    if (png_ptr->row_buf[0] > PNG_FILTER_VALUE_NONE) {
      if (png_ptr->row_buf[0] < PNG_FILTER_VALUE_LAST)
        png_read_filter_row (png_ptr, &row_info, png_ptr->row_buf + 1,
                             png_ptr->prev_row + 1, png_ptr->row_buf[0]);
      else
        png_error (png_ptr, "bad adaptive filter value");
    }
  
    /* libpng 1.5.6: the following line was copying png_ptr->rowbytes before
      * 1.5.6, while the buffer really is this big in current versions of libpng
      * it may not be in the future, so this was changed just to copy the
      * interlaced count:
      */
    memcpy (png_ptr->prev_row, png_ptr->row_buf, row_info.rowbytes + 1);
  
  #ifdef PNG_MNG_FEATURES_SUPPORTED
    if ((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) != 0 &&
        (png_ptr->filter_type == PNG_INTRAPIXEL_DIFFERENCING)) {
      /* Intrapixel differencing */
      png_do_read_intrapixel (&row_info, png_ptr->row_buf + 1);
    }
  #endif
  
  #ifdef PNG_READ_TRANSFORMS_SUPPORTED
    if (png_ptr->transformations)
      png_do_read_transformations (png_ptr, &row_info);
  #endif
  
    /* The transformed pixel depth should match the depth now in row_info. */
    if (png_ptr->transformed_pixel_depth == 0) {
      png_ptr->transformed_pixel_depth = row_info.pixel_depth;
      if (row_info.pixel_depth > png_ptr->maximum_pixel_depth)
        png_error (png_ptr, "sequential row overflow");
    }
  
    else if (png_ptr->transformed_pixel_depth != row_info.pixel_depth)
      png_error (png_ptr, "internal sequential row size calculation error");
  
  #ifdef PNG_READ_INTERLACING_SUPPORTED
    /* Expand interlaced rows to full size */
    if (png_ptr->interlaced != 0 &&
        (png_ptr->transformations & PNG_INTERLACE) != 0) {
      if (png_ptr->pass < 6)
        png_do_read_interlace (&row_info, png_ptr->row_buf + 1, png_ptr->pass,
                               png_ptr->transformations);
  
      if (dsp_row != NULL)
        png_combine_row (png_ptr, dsp_row, 1/*display*/);
  
      if (row != NULL)
        png_combine_row (png_ptr, row, 0/*row*/);
    }
  
    else
  #endif
    {
      if (row != NULL)
        png_combine_row (png_ptr, row, -1/*ignored*/);
  
      if (dsp_row != NULL)
        png_combine_row (png_ptr, dsp_row, -1/*ignored*/);
    }
    png_read_finish_row (png_ptr);
  
    if (png_ptr->read_row_fn != NULL)
      (*(png_ptr->read_row_fn)) (png_ptr, png_ptr->row_number, png_ptr->pass);
  
  }
  
  #endif /* SEQUENTIAL_READ */
  
  #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
  
  /* Read one or more rows of image data.  If the image is interlaced,
   * and png_set_interlace_handling() has been called, the rows need to
   * contain the contents of the rows from the previous pass.  If the
   * image has alpha or transparency, and png_handle_alpha()[*] has been
   * called, the rows contents must be initialized to the contents of the
   * screen.
   *
   * "row" holds the actual image, and pixels are placed in it
   * as they arrive.  If the image is displayed after each pass, it will
   * appear to "sparkle" in.  "display_row" can be used to display a
   * "chunky" progressive image, with finer detail added as it becomes
   * available.  If you do not want this "chunky" display, you may pass
   * NULL for display_row.  If you do not want the sparkle display, and
   * you have not called png_handle_alpha(), you may pass NULL for rows.
   * If you have called png_handle_alpha(), and the image has either an
   * alpha channel or a transparency chunk, you must provide a buffer for
   * rows.  In this case, you do not have to provide a display_row buffer
   * also, but you may.  If the image is not interlaced, or if you have
   * not called png_set_interlace_handling(), the display_row buffer will
   * be ignored, so pass NULL to it.
   *
   * [*] png_handle_alpha() does not exist yet, as of this version of libpng
   */
  
  void PNGAPI
  png_read_rows (png_structrp png_ptr, png_bytepp row,
                 png_bytepp display_row, png_uint_32 num_rows) {
    png_uint_32 i;
    png_bytepp rp;
    png_bytepp dp;
  
    png_debug(1, "in png_read_rows");
  
    if (png_ptr == NULL)
      return;
  
    rp = row;
    dp = display_row;
    if (rp != NULL && dp != NULL)
      for (i = 0; i < num_rows; i++) {
        png_bytep rptr = *rp++;
        png_bytep dptr = *dp++;
  
        png_read_row (png_ptr, rptr, dptr);
      }
  
    else if (rp != NULL)
      for (i = 0; i < num_rows; i++) {
        png_bytep rptr = *rp;
        png_read_row (png_ptr, rptr, NULL);
        rp++;
      }
  
    else if (dp != NULL)
      for (i = 0; i < num_rows; i++) {
        png_bytep dptr = *dp;
        png_read_row (png_ptr, NULL, dptr);
        dp++;
      }
  }
  
  #endif /* SEQUENTIAL_READ */
  
  #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
  
  /* Read the entire image.  If the image has an alpha channel or a tRNS
   * chunk, and you have called png_handle_alpha()[*], you will need to
   * initialize the image to the current image that PNG will be overlaying.
   * We set the num_rows again here, in case it was incorrectly set in
   * png_read_start_row() by a call to png_read_update_info() or
   * png_start_read_image() if png_set_interlace_handling() wasn't called
   * prior to either of these functions like it should have been.  You can
   * only call this function once.  If you desire to have an image for
   * each pass of a interlaced image, use png_read_rows() instead.
   *
   * [*] png_handle_alpha() does not exist yet, as of this version of libpng
   */
  void PNGAPI
  png_read_image (png_structrp png_ptr, png_bytepp image) {
    png_uint_32 i, image_height;
    int pass, j;
    png_bytepp rp;
  
    png_debug(1, "in png_read_image");
  
    if (png_ptr == NULL)
      return;
  
  #ifdef PNG_READ_INTERLACING_SUPPORTED
    if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0) {
      pass = png_set_interlace_handling (png_ptr);
      /* And make sure transforms are initialized. */
      png_start_read_image (png_ptr);
    }
    else {
      if (png_ptr->interlaced != 0 &&
          (png_ptr->transformations & PNG_INTERLACE) == 0) {
        /* Caller called png_start_read_image or png_read_update_info without
            * first turning on the PNG_INTERLACE transform.  We can fix this here,
            * but the caller should do it!
            */
        png_warning (png_ptr, "Interlace handling should be turned on when "
                              "using png_read_image");
        /* Make sure this is set correctly */
        png_ptr->num_rows = png_ptr->height;
      }
  
      /* Obtain the pass number, which also turns on the PNG_INTERLACE flag in
         * the above error case.
         */
      pass = png_set_interlace_handling (png_ptr);
    }
  #else
                                                                                                                            if (png_ptr->interlaced)
        png_error(png_ptr,
            "Cannot read interlaced image -- interlace handler disabled");
  
     pass = 1;
  #endif
  
    image_height = png_ptr->height;
  
    for (j = 0; j < pass; j++) {
      rp = image;
      for (i = 0; i < image_height; i++) {
        png_read_row (png_ptr, *rp, NULL);
        rp++;
      }
    }
  }
  
  #endif /* SEQUENTIAL_READ */
  
  #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
  
  /* Read the end of the PNG file.  Will not read past the end of the
   * file, will verify the end is accurate, and will read any comments
   * or time information at the end of the file, if info is not NULL.
   */
  void PNGAPI
  png_read_end (png_structrp png_ptr, png_inforp info_ptr) {
  #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
    int keep;
  #endif
  
    png_debug(1, "in png_read_end");
  
    if (png_ptr == NULL)
      return;
  
    /* If png_read_end is called in the middle of reading the rows there may
      * still be pending IDAT data and an owned zstream.  Deal with this here.
      */
  #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
    if (png_chunk_unknown_handling (png_ptr, png_IDAT) == 0)
  #endif
      png_read_finish_IDAT (png_ptr);
  
  #ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
    /* Report invalid palette index; added at libng-1.5.10 */
    if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
        png_ptr->num_palette_max > png_ptr->num_palette)
      png_benign_error (png_ptr, "Read palette index exceeding num_palette");
  #endif
  
    do {
      png_uint_32 length = png_read_chunk_header (png_ptr);
      png_uint_32 chunk_name = png_ptr->chunk_name;
  
      if (chunk_name != png_IDAT)
        png_ptr->mode |= PNG_HAVE_CHUNK_AFTER_IDAT;
  
      if (chunk_name == png_IEND)
        png_handle_IEND (png_ptr, info_ptr, length);
  
      else if (chunk_name == png_IHDR)
        png_handle_IHDR (png_ptr, info_ptr, length);
  
      else if (info_ptr == NULL)
        png_crc_finish (png_ptr, length);
  
  #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
      else if ((keep = png_chunk_unknown_handling (png_ptr, chunk_name)) != 0) {
        if (chunk_name == png_IDAT) {
          if ((length > 0 && !(png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED))
              || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT) != 0)
            png_benign_error (png_ptr, ".Too many IDATs found");
        }
        png_handle_unknown (png_ptr, info_ptr, length, keep);
        if (chunk_name == png_PLTE)
          png_ptr->mode |= PNG_HAVE_PLTE;
      }
  #endif
  
      else if (chunk_name == png_IDAT) {
        /* Zero length IDATs are legal after the last IDAT has been
            * read, but not after other chunks have been read.  1.6 does not
            * always read all the deflate data; specifically it cannot be relied
            * upon to read the Adler32 at the end.  If it doesn't ignore IDAT
            * chunks which are longer than zero as well:
            */
        if ((length > 0 && !(png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED))
            || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT) != 0)
          png_benign_error (png_ptr, "..Too many IDATs found");
  
        png_crc_finish (png_ptr, length);
      }
      else if (chunk_name == png_PLTE)
        png_handle_PLTE (png_ptr, info_ptr, length);
  
  #ifdef PNG_READ_bKGD_SUPPORTED
      else if (chunk_name == png_bKGD)
        png_handle_bKGD (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_cHRM_SUPPORTED
      else if (chunk_name == png_cHRM)
        png_handle_cHRM (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_eXIf_SUPPORTED
      else if (chunk_name == png_eXIf)
        png_handle_eXIf (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_gAMA_SUPPORTED
      else if (chunk_name == png_gAMA)
        png_handle_gAMA (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_hIST_SUPPORTED
      else if (chunk_name == png_hIST)
        png_handle_hIST (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_oFFs_SUPPORTED
      else if (chunk_name == png_oFFs)
        png_handle_oFFs (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_pCAL_SUPPORTED
      else if (chunk_name == png_pCAL)
        png_handle_pCAL (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_sCAL_SUPPORTED
      else if (chunk_name == png_sCAL)
        png_handle_sCAL (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_pHYs_SUPPORTED
      else if (chunk_name == png_pHYs)
        png_handle_pHYs (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_sBIT_SUPPORTED
      else if (chunk_name == png_sBIT)
        png_handle_sBIT (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_sRGB_SUPPORTED
      else if (chunk_name == png_sRGB)
        png_handle_sRGB (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_iCCP_SUPPORTED
      else if (chunk_name == png_iCCP)
        png_handle_iCCP (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_sPLT_SUPPORTED
      else if (chunk_name == png_sPLT)
        png_handle_sPLT (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_tEXt_SUPPORTED
      else if (chunk_name == png_tEXt)
        png_handle_tEXt (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_tIME_SUPPORTED
      else if (chunk_name == png_tIME)
        png_handle_tIME (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_tRNS_SUPPORTED
      else if (chunk_name == png_tRNS)
        png_handle_tRNS (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_zTXt_SUPPORTED
      else if (chunk_name == png_zTXt)
        png_handle_zTXt (png_ptr, info_ptr, length);
  #endif
  
  #ifdef PNG_READ_iTXt_SUPPORTED
      else if (chunk_name == png_iTXt)
        png_handle_iTXt (png_ptr, info_ptr, length);
  #endif
  
      else
        png_handle_unknown (png_ptr, info_ptr, length,
                            PNG_HANDLE_CHUNK_AS_DEFAULT);
    }
    while ((png_ptr->mode & PNG_HAVE_IEND) == 0);
  }
  
  #endif /* SEQUENTIAL_READ */
  
  /* Free all memory used in the read struct */
  static void
  png_read_destroy (png_structrp png_ptr) {
    png_debug(1, "in png_read_destroy");
  
  #ifdef PNG_READ_GAMMA_SUPPORTED
    png_destroy_gamma_table (png_ptr);
  #endif
  
    png_free (png_ptr, png_ptr->big_row_buf);
    png_ptr->big_row_buf = NULL;
    png_free (png_ptr, png_ptr->big_prev_row);
    png_ptr->big_prev_row = NULL;
    png_free (png_ptr, png_ptr->read_buffer);
    png_ptr->read_buffer = NULL;
  
  #ifdef PNG_READ_QUANTIZE_SUPPORTED
    png_free (png_ptr, png_ptr->palette_lookup);
    png_ptr->palette_lookup = NULL;
    png_free (png_ptr, png_ptr->quantize_index);
    png_ptr->quantize_index = NULL;
  #endif
  
    if ((png_ptr->free_me & PNG_FREE_PLTE) != 0) {
      png_zfree (png_ptr, png_ptr->palette);
      png_ptr->palette = NULL;
    }
    png_ptr->free_me &= ~PNG_FREE_PLTE;
  
  #if defined(PNG_tRNS_SUPPORTED) || \
      defined(PNG_READ_EXPAND_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
    if ((png_ptr->free_me & PNG_FREE_TRNS) != 0) {
      png_free (png_ptr, png_ptr->trans_alpha);
      png_ptr->trans_alpha = NULL;
    }
    png_ptr->free_me &= ~PNG_FREE_TRNS;
  #endif
  
    inflateEnd (&png_ptr->zstream);
  
  #ifdef PNG_PROGRESSIVE_READ_SUPPORTED
    png_free (png_ptr, png_ptr->save_buffer);
    png_ptr->save_buffer = NULL;
  #endif
  
  #if defined(PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED) && \
     defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
    png_free (png_ptr, png_ptr->unknown_chunk.data);
    png_ptr->unknown_chunk.data = NULL;
  #endif
  
  #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
    png_free (png_ptr, png_ptr->chunk_list);
    png_ptr->chunk_list = NULL;
  #endif
  
  #if defined(PNG_READ_EXPAND_SUPPORTED) && \
      defined(PNG_ARM_NEON_IMPLEMENTATION)
                                                                                                                            png_free(png_ptr, png_ptr->riffled_palette);
     png_ptr->riffled_palette = NULL;
  #endif
  
    /* NOTE: the 'setjmp' buffer may still be allocated and the memory and error
      * callbacks are still set at this point.  They are required to complete the
      * destruction of the png_struct itself.
      */
  }
  
  /* Free all memory used by the read */
  void PNGAPI
  png_destroy_read_struct (png_structpp png_ptr_ptr, png_infopp info_ptr_ptr,
                           png_infopp end_info_ptr_ptr) {
    png_structrp png_ptr = NULL;
  
    png_debug(1, "in png_destroy_read_struct");
  
    if (png_ptr_ptr != NULL)
      png_ptr = *png_ptr_ptr;
  
    if (png_ptr == NULL)
      return;
  
    /* libpng 1.6.0: use the API to destroy info structs to ensure consistent
      * behavior.  Prior to 1.6.0 libpng did extra 'info' destruction in this API.
      * The extra was, apparently, unnecessary yet this hides memory leak bugs.
      */
    png_destroy_info_struct (png_ptr, end_info_ptr_ptr);
    png_destroy_info_struct (png_ptr, info_ptr_ptr);
  
    *png_ptr_ptr = NULL;
    png_read_destroy (png_ptr);
    png_destroy_png_struct (png_ptr);
  }
  
  void PNGAPI
  png_set_read_status_fn (png_structrp png_ptr, png_read_status_ptr read_row_fn) {
    if (png_ptr == NULL)
      return;
  
    png_ptr->read_row_fn = read_row_fn;
  }
  
  #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
  #ifdef PNG_INFO_IMAGE_SUPPORTED
  
  void PNGAPI
  png_read_png (png_structrp png_ptr, png_inforp info_ptr,
                int transforms, voidp params) {
    if (png_ptr == NULL || info_ptr == NULL)
      return;
  
    /* png_read_info() gives us all of the information from the
      * PNG file before the first IDAT (image data chunk).
      */
    png_read_info (png_ptr, info_ptr);
    if (info_ptr->height > PNG_UINT_32_MAX / (sizeof (png_bytep)))
      png_error (png_ptr, "Image is too high to process with png_read_png()");
  
    /* -------------- image transformations start here ------------------- */
    /* libpng 1.6.10: add code to cause a png_app_error if a selected TRANSFORM
      * is not implemented.  This will only happen in de-configured (non-default)
      * libpng builds.  The results can be unexpected - png_read_png may return
      * short or mal-formed rows because the transform is skipped.
      */
  
    /* Tell libpng to strip 16-bit/color files down to 8 bits per color.
      */
    if ((transforms & PNG_TRANSFORM_SCALE_16) != 0)
      /* Added at libpng-1.5.4. "strip_16" produces the same result that it
         * did in earlier versions, while "scale_16" is now more accurate.
         */
  #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
      png_set_scale_16 (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_SCALE_16 not supported");
  #endif
  
    /* If both SCALE and STRIP are required pngrtran will effectively cancel the
      * latter by doing SCALE first.  This is ok and allows apps not to check for
      * which is supported to get the right answer.
      */
    if ((transforms & PNG_TRANSFORM_STRIP_16) != 0)
  #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
      png_set_strip_16 (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_STRIP_16 not supported");
  #endif
  
    /* Strip alpha bytes from the input data without combining with
      * the background (not recommended).
      */
    if ((transforms & PNG_TRANSFORM_STRIP_ALPHA) != 0)
  #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
      png_set_strip_alpha (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_STRIP_ALPHA not supported");
  #endif
  
    /* Extract multiple pixels with bit depths of 1, 2, or 4 from a single
      * byte into separate bytes (useful for paletted and grayscale images).
      */
    if ((transforms & PNG_TRANSFORM_PACKING) != 0)
  #ifdef PNG_READ_PACK_SUPPORTED
      png_set_packing (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_PACKING not supported");
  #endif
  
    /* Change the order of packed pixels to least significant bit first
      * (not useful if you are using png_set_packing).
      */
    if ((transforms & PNG_TRANSFORM_PACKSWAP) != 0)
  #ifdef PNG_READ_PACKSWAP_SUPPORTED
      png_set_packswap (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_PACKSWAP not supported");
  #endif
  
    /* Expand paletted colors into true RGB triplets
      * Expand grayscale images to full 8 bits from 1, 2, or 4 bits/pixel
      * Expand paletted or RGB images with transparency to full alpha
      * channels so the data will be available as RGBA quartets.
      */
    if ((transforms & PNG_TRANSFORM_EXPAND) != 0)
  #ifdef PNG_READ_EXPAND_SUPPORTED
      png_set_expand (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_EXPAND not supported");
  #endif
  
    /* We don't handle background color or gamma transformation or quantizing.
      */
  
    /* Invert monochrome files to have 0 as white and 1 as black
      */
    if ((transforms & PNG_TRANSFORM_INVERT_MONO) != 0)
  #ifdef PNG_READ_INVERT_SUPPORTED
      png_set_invert_mono (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_MONO not supported");
  #endif
  
    /* If you want to shift the pixel values from the range [0,255] or
      * [0,65535] to the original [0,7] or [0,31], or whatever range the
      * colors were originally in:
      */
    if ((transforms & PNG_TRANSFORM_SHIFT) != 0)
  #ifdef PNG_READ_SHIFT_SUPPORTED
      if ((info_ptr->valid & PNG_INFO_sBIT) != 0)
        png_set_shift (png_ptr, &info_ptr->sig_bit);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_SHIFT not supported");
  #endif
  
    /* Flip the RGB pixels to BGR (or RGBA to BGRA) */
    if ((transforms & PNG_TRANSFORM_BGR) != 0)
  #ifdef PNG_READ_BGR_SUPPORTED
      png_set_bgr (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_BGR not supported");
  #endif
  
    /* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
    if ((transforms & PNG_TRANSFORM_SWAP_ALPHA) != 0)
  #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
      png_set_swap_alpha (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ALPHA not supported");
  #endif
  
    /* Swap bytes of 16-bit files to least significant byte first */
    if ((transforms & PNG_TRANSFORM_SWAP_ENDIAN) != 0)
  #ifdef PNG_READ_SWAP_SUPPORTED
      png_set_swap (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ENDIAN not supported");
  #endif
  
  /* Added at libpng-1.2.41 */
    /* Invert the alpha channel from opacity to transparency */
    if ((transforms & PNG_TRANSFORM_INVERT_ALPHA) != 0)
  #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
      png_set_invert_alpha (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_ALPHA not supported");
  #endif
  
  /* Added at libpng-1.2.41 */
    /* Expand grayscale image to RGB */
    if ((transforms & PNG_TRANSFORM_GRAY_TO_RGB) != 0)
  #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
      png_set_gray_to_rgb (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_GRAY_TO_RGB not supported");
  #endif
  
  /* Added at libpng-1.5.4 */
    if ((transforms & PNG_TRANSFORM_EXPAND_16) != 0)
  #ifdef PNG_READ_EXPAND_16_SUPPORTED
      png_set_expand_16 (png_ptr);
  #else
    png_app_error(png_ptr, "PNG_TRANSFORM_EXPAND_16 not supported");
  #endif
  
    /* We don't handle adding filler bytes */
  
    /* We use png_read_image and rely on that for interlace handling, but we also
      * call png_read_update_info therefore must turn on interlace handling now:
      */
    (void) png_set_interlace_handling (png_ptr);
  
    /* Optional call to gamma correct and add the background to the palette
      * and update info structure.  REQUIRED if you are expecting libpng to
      * update the palette for you (i.e., you selected such a transform above).
      */
    png_read_update_info (png_ptr, info_ptr);
  
    /* -------------- image transformations end here ------------------- */
  
    png_free_data (png_ptr, info_ptr, PNG_FREE_ROWS, 0);
    if (info_ptr->row_pointers == NULL) {
      png_uint_32 iptr;
  
      info_ptr->row_pointers = png_voidcast(png_bytepp, png_malloc (png_ptr,
                                                                    info_ptr->height * (sizeof (png_bytep))));
  
      for (iptr = 0; iptr < info_ptr->height; iptr++)
        info_ptr->row_pointers[iptr] = NULL;
  
      info_ptr->free_me |= PNG_FREE_ROWS;
  
      for (iptr = 0; iptr < info_ptr->height; iptr++)
        info_ptr->row_pointers[iptr] = png_voidcast(png_bytep,
                                                    png_malloc (png_ptr, info_ptr->rowbytes));
    }
  
    png_read_image (png_ptr, info_ptr->row_pointers);
    info_ptr->valid |= PNG_INFO_IDAT;
  
    /* Read rest of file, and get additional chunks in info_ptr - REQUIRED */
    png_read_end (png_ptr, info_ptr);
  
    PNG_UNUSED(params)
  }
  
  #endif /* INFO_IMAGE */
  #endif /* SEQUENTIAL_READ */
  
  #ifdef PNG_SIMPLIFIED_READ_SUPPORTED
  /* SIMPLIFIED READ
   *
   * This code currently relies on the sequential reader, though it could easily
   * be made to work with the progressive one.
   */
  /* Arguments to png_image_finish_read: */
  
  /* Encoding of PNG data (used by the color-map code) */
  #  define P_NOTSET  0 /* File encoding not yet known */
  #  define P_sRGB    1 /* 8-bit encoded to sRGB gamma */
  #  define P_LINEAR  2 /* 16-bit linear: not encoded, NOT pre-multiplied! */
  #  define P_FILE    3 /* 8-bit encoded to file gamma, not sRGB or linear */
  #  define P_LINEAR8 4 /* 8-bit linear: only from a file value */
  
  /* Color-map processing: after libpng has run on the PNG image further
   * processing may be needed to convert the data to color-map indices.
   */
  #define PNG_CMAP_NONE      0
  #define PNG_CMAP_GA        1 /* Process GA data to a color-map with alpha */
  #define PNG_CMAP_TRANS     2 /* Process GA data to a background index */
  #define PNG_CMAP_RGB       3 /* Process RGB data */
  #define PNG_CMAP_RGB_ALPHA 4 /* Process RGBA data */
  
  /* The following document where the background is for each processing case. */
  #define PNG_CMAP_NONE_BACKGROUND      256
  #define PNG_CMAP_GA_BACKGROUND        231
  #define PNG_CMAP_TRANS_BACKGROUND     254
  #define PNG_CMAP_RGB_BACKGROUND       256
  #define PNG_CMAP_RGB_ALPHA_BACKGROUND 216
  
  typedef struct {
    /* Arguments: */
    png_imagep image;
    png_voidp buffer;
    png_int_32 row_stride;
    png_voidp colormap;
    png_const_colorp background;
    /* Local variables: */
    png_voidp local_row;
    png_voidp first_row;
    ptrdiff_t row_bytes;           /* step between rows */
    int file_encoding;       /* E_ values above */
    png_fixed_point gamma_to_linear;     /* For P_FILE, reciprocal of gamma */
    int colormap_processing; /* PNG_CMAP_ values above */
  } png_image_read_control;
  
  /* Do all the *safe* initialization - 'safe' means that png_error won't be
   * called, so setting up the jmp_buf is not required.  This means that anything
   * called from here must *not* call png_malloc - it has to call png_malloc_warn
   * instead so that control is returned safely back to this routine.
   */
  static int
  png_image_read_init (png_imagep image) {
    if (image->opaque == NULL) {
      png_structp png_ptr = png_create_read_struct (PNG_LIBPNG_VER_STRING, image,
                                                    png_safe_error, png_safe_warning);
  
      /* And set the rest of the structure to NULL to ensure that the various
         * fields are consistent.
         */
      memset (image, 0, (sizeof *image));
      image->version = PNG_IMAGE_VERSION;
  
      if (png_ptr != NULL) {
        png_infop info_ptr = png_create_info_struct (png_ptr);
  
        if (info_ptr != NULL) {
          png_controlp control = png_voidcast(png_controlp,
                                              png_malloc_warn (png_ptr, (sizeof *control)));
  
          if (control != NULL) {
            memset (control, 0, (sizeof *control));
  
            control->png_ptr = png_ptr;
            control->info_ptr = info_ptr;
            control->for_write = 0;
  
            image->opaque = control;
            return 1;
          }
  
          /* Error clean up */
          png_destroy_info_struct (png_ptr, &info_ptr);
        }
  
        png_destroy_read_struct (&png_ptr, NULL, NULL);
      }
  
      return png_image_error (image, "png_image_read: out of memory");
    }
  
    return png_image_error (image, "png_image_read: opaque pointer not NULL");
  }
  
  /* Utility to find the base format of a PNG file from a png_struct. */
  static png_uint_32
  png_image_format (png_structrp png_ptr) {
    png_uint_32 format = 0;
  
    if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) != 0)
      format |= PNG_FORMAT_FLAG_COLOR;
  
    if ((png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0)
      format |= PNG_FORMAT_FLAG_ALPHA;
  
      /* Use png_ptr here, not info_ptr, because by examination png_handle_tRNS
      * sets the png_struct fields; that's all we are interested in here.  The
      * precise interaction with an app call to png_set_tRNS and PNG file reading
      * is unclear.
      */
    else if (png_ptr->num_trans > 0)
      format |= PNG_FORMAT_FLAG_ALPHA;
  
    if (png_ptr->bit_depth == 16)
      format |= PNG_FORMAT_FLAG_LINEAR;
  
    if ((png_ptr->color_type & PNG_COLOR_MASK_PALETTE) != 0)
      format |= PNG_FORMAT_FLAG_COLORMAP;
  
    return format;
  }
  
  /* Is the given gamma significantly different from sRGB?  The test is the same
   * one used in pngrtran.c when deciding whether to do gamma correction.  The
   * arithmetic optimizes the division by using the fact that the inverse of the
   * file sRGB gamma is 2.2
   */
  static int
  png_gamma_not_sRGB (png_fixed_point g) {
    if (g < PNG_FP_1) {
      /* An uninitialized gamma is assumed to be sRGB for the simplified API. */
      if (g == 0)
        return 0;
  
      return png_gamma_significant ((g * 11 + 2) / 5 /* i.e. *2.2, rounded */);
    }
  
    return 1;
  }
  
  /* Do the main body of a 'png_image_begin_read' function; read the PNG file
   * header and fill in all the information.  This is executed in a safe context,
   * unlike the init routine above.
   */
  static int
  png_image_read_header (png_voidp argument) {
    png_imagep image = png_voidcast(png_imagep, argument);
    png_structrp png_ptr = image->opaque->png_ptr;
    png_inforp info_ptr = image->opaque->info_ptr;
  
  #ifdef PNG_BENIGN_ERRORS_SUPPORTED
    png_set_benign_errors (png_ptr, 1/*warn*/);
  #endif
    png_read_info (png_ptr, info_ptr);
  
    /* Do this the fast way; just read directly out of png_struct. */
    image->width = png_ptr->width;
    image->height = png_ptr->height;
  
    {
      png_uint_32 format = png_image_format (png_ptr);
  
      image->format = format;
  
  #ifdef PNG_COLORSPACE_SUPPORTED
      /* Does the colorspace match sRGB?  If there is no color endpoint
         * (colorant) information assume yes, otherwise require the
         * 'ENDPOINTS_MATCHP_sRGB' colorspace flag to have been set.  If the
         * colorspace has been determined to be invalid ignore it.
         */
      if ((format & PNG_FORMAT_FLAG_COLOR) != 0 && ((png_ptr->colorspace.flags
                                                     & (PNG_COLORSPACE_HAVE_ENDPOINTS
                                                        | PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB |
                                                        PNG_COLORSPACE_INVALID)) == PNG_COLORSPACE_HAVE_ENDPOINTS))
        image->flags |= PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB;
  #endif
    }
  
    /* We need the maximum number of entries regardless of the format the
      * application sets here.
      */
    {
      png_uint_32 cmap_entries;
  
      switch (png_ptr->color_type) {
        case PNG_COLOR_TYPE_GRAY:
          cmap_entries = 1U << png_ptr->bit_depth;
          break;
  
        case PNG_COLOR_TYPE_PALETTE:
          cmap_entries = (png_uint_32) png_ptr->num_palette;
          break;
  
        default:
          cmap_entries = 256;
          break;
      }
  
      if (cmap_entries > 256)
        cmap_entries = 256;
  
      image->colormap_entries = cmap_entries;
    }
  
    return 1;
  }
  
  #ifdef PNG_STDIO_SUPPORTED
  
  int PNGAPI
  png_image_begin_read_from_stdio (png_imagep image, FILE* file) {
    if (image != NULL && image->version == PNG_IMAGE_VERSION) {
      if (file != NULL) {
        if (png_image_read_init (image) != 0) {
          /* This is slightly evil, but png_init_io doesn't do anything other
               * than this and we haven't changed the standard IO functions so
               * this saves a 'safe' function.
               */
          image->opaque->png_ptr->io_ptr = file;
          return png_safe_execute (image, png_image_read_header, image);
        }
      }
  
      else
        return png_image_error (image,
                                "png_image_begin_read_from_stdio: invalid argument");
    }
  
    else if (image != NULL)
      return png_image_error (image,
                              "png_image_begin_read_from_stdio: incorrect PNG_IMAGE_VERSION");
  
    return 0;
  }
  
  int PNGAPI
  png_image_begin_read_from_file (png_imagep image, const char* file_name) {
    if (image != NULL && image->version == PNG_IMAGE_VERSION) {
      if (file_name != NULL) {
        FILE* fp = fopen (file_name, "rb");
  
        if (fp != NULL) {
          if (png_image_read_init (image) != 0) {
            image->opaque->png_ptr->io_ptr = fp;
            image->opaque->owned_file = 1;
            return png_safe_execute (image, png_image_read_header, image);
          }
  
          /* Clean up: just the opened file. */
          (void) fclose (fp);
        }
  
        else
          return png_image_error (image, strerror (errno));
      }
  
      else
        return png_image_error (image,
                                "png_image_begin_read_from_file: invalid argument");
    }
  
    else if (image != NULL)
      return png_image_error (image,
                              "png_image_begin_read_from_file: incorrect PNG_IMAGE_VERSION");
  
    return 0;
  }
  
  #endif /* STDIO */
  
  static void PNGCBAPI
  png_image_memory_read (png_structp png_ptr, png_bytep out, size_t need) {
    if (png_ptr != NULL) {
      png_imagep image = png_voidcast(png_imagep, png_ptr->io_ptr);
      if (image != NULL) {
        png_controlp cp = image->opaque;
        if (cp != NULL) {
          png_const_bytep memory = cp->memory;
          size_t size = cp->size;
  
          if (memory != NULL && size >= need) {
            memcpy (out, memory, need);
            cp->memory = memory + need;
            cp->size = size - need;
            return;
          }
  
          png_error (png_ptr, "read beyond end of data");
        }
      }
  
      png_error (png_ptr, "invalid memory read");
    }
  }
  
  int PNGAPI png_image_begin_read_from_memory (png_imagep image,
                                               png_const_voidp memory, size_t size) {
    if (image != NULL && image->version == PNG_IMAGE_VERSION) {
      if (memory != NULL && size > 0) {
        if (png_image_read_init (image) != 0) {
          /* Now set the IO functions to read from the memory buffer and
               * store it into io_ptr.  Again do this in-place to avoid calling a
               * libpng function that requires error handling.
               */
          image->opaque->memory = png_voidcast(png_const_bytep, memory);
          image->opaque->size = size;
          image->opaque->png_ptr->io_ptr = image;
          image->opaque->png_ptr->read_data_fn = png_image_memory_read;
  
          return png_safe_execute (image, png_image_read_header, image);
        }
      }
  
      else
        return png_image_error (image,
                                "png_image_begin_read_from_memory: invalid argument");
    }
  
    else if (image != NULL)
      return png_image_error (image,
                              "png_image_begin_read_from_memory: incorrect PNG_IMAGE_VERSION");
  
    return 0;
  }
  
  /* Utility function to skip chunks that are not used by the simplified image
   * read functions and an appropriate macro to call it.
   */
  #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
  
  static void
  png_image_skip_unused_chunks (png_structrp png_ptr) {
    /* Prepare the reader to ignore all recognized chunks whose data will not
      * be used, i.e., all chunks recognized by libpng except for those
      * involved in basic image reading:
      *
      *    IHDR, PLTE, IDAT, IEND
      *
      * Or image data handling:
      *
      *    tRNS, bKGD, gAMA, cHRM, sRGB, [iCCP] and sBIT.
      *
      * This provides a small performance improvement and eliminates any
      * potential vulnerability to security problems in the unused chunks.
      *
      * At present the iCCP chunk data isn't used, so iCCP chunk can be ignored
      * too.  This allows the simplified API to be compiled without iCCP support,
      * however if the support is there the chunk is still checked to detect
      * errors (which are unfortunately quite common.)
      */
    {
      static const png_byte chunks_to_process[] = {
          98, 75, 71, 68, '\0',  /* bKGD */
          99, 72, 82, 77, '\0',  /* cHRM */
          103, 65, 77, 65, '\0',  /* gAMA */
  #        ifdef PNG_READ_iCCP_SUPPORTED
          105, 67, 67, 80, '\0',  /* iCCP */
  #        endif
          115, 66, 73, 84, '\0',  /* sBIT */
          115, 82, 71, 66, '\0',  /* sRGB */
      };
  
      /* Ignore unknown chunks and all other chunks except for the
          * IHDR, PLTE, tRNS, IDAT, and IEND chunks.
          */
      png_set_keep_unknown_chunks (png_ptr, PNG_HANDLE_CHUNK_NEVER,
                                   NULL, -1);
  
      /* But do not ignore image data handling chunks */
      png_set_keep_unknown_chunks (png_ptr, PNG_HANDLE_CHUNK_AS_DEFAULT,
                                   chunks_to_process, (int)/*SAFE*/(sizeof chunks_to_process) / 5);
    }
  }
  
  #  define PNG_SKIP_CHUNKS(p) png_image_skip_unused_chunks(p)
  #else
  #  define PNG_SKIP_CHUNKS(p) ((void)0)
  #endif /* HANDLE_AS_UNKNOWN */
  
  /* The following macro gives the exact rounded answer for all values in the
   * range 0..255 (it actually divides by 51.2, but the rounding still generates
   * the correct numbers 0..5
   */
  #define PNG_DIV51(v8) (((v8) * 5 + 130) >> 8)
  
  /* Utility functions to make particular color-maps */
  static void
  set_file_encoding (png_image_read_control* display) {
    png_fixed_point g = display->image->opaque->png_ptr->colorspace.gamma;
    if (png_gamma_significant (g) != 0) {
      if (png_gamma_not_sRGB (g) != 0) {
        display->file_encoding = P_FILE;
        display->gamma_to_linear = png_reciprocal (g);
      }
  
      else
        display->file_encoding = P_sRGB;
    }
  
    else
      display->file_encoding = P_LINEAR8;
  }
  
  static unsigned int
  decode_gamma (png_image_read_control* display, png_uint_32 value, int encoding) {
    if (encoding == P_FILE) /* double check */
      encoding = display->file_encoding;
  
    if (encoding == P_NOTSET) /* must be the file encoding */
    {
      set_file_encoding (display);
      encoding = display->file_encoding;
    }
  
    switch (encoding) {
      case P_FILE:
        value = png_gamma_16bit_correct (value * 257, display->gamma_to_linear);
        break;
  
      case P_sRGB:
        value = png_sRGB_table[value];
        break;
  
      case P_LINEAR:
        break;
  
      case P_LINEAR8:
        value *= 257;
        break;
  
  #ifdef __GNUC__
      default:
        png_error (display->image->opaque->png_ptr,
                   "unexpected encoding (internal error)");
  #endif
    }
  
    return value;
  }
  
  static png_uint_32
  png_colormap_compose (png_image_read_control* display,
                        png_uint_32 foreground, int foreground_encoding, png_uint_32 alpha,
                        png_uint_32 background, int encoding) {
    /* The file value is composed on the background, the background has the given
      * encoding and so does the result, the file is encoded with P_FILE and the
      * file and alpha are 8-bit values.  The (output) encoding will always be
      * P_LINEAR or P_sRGB.
      */
    png_uint_32 f = decode_gamma (display, foreground, foreground_encoding);
    png_uint_32 b = decode_gamma (display, background, encoding);
  
    /* The alpha is always an 8-bit value (it comes from the palette), the value
      * scaled by 255 is what PNG_sRGB_FROM_LINEAR requires.
      */
    f = f * alpha + b * (255 - alpha);
  
    if (encoding == P_LINEAR) {
      /* Scale to 65535; divide by 255, approximately (in fact this is extremely
         * accurate, it divides by 255.00000005937181414556, with no overflow.)
         */
      f *= 257; /* Now scaled by 65535 */
      f += f >> 16;
      f = (f + 32768) >> 16;
    }
  
    else /* P_sRGB */
      f = PNG_sRGB_FROM_LINEAR(f);
  
    return f;
  }
  
  /* NOTE: P_LINEAR values to this routine must be 16-bit, but P_FILE values must
   * be 8-bit.
   */
  static void
  png_create_colormap_entry (png_image_read_control* display,
                             png_uint_32 ip, png_uint_32 red, png_uint_32 green, png_uint_32 blue,
                             png_uint_32 alpha, int encoding) {
    png_imagep image = display->image;
    int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
                          P_LINEAR : P_sRGB;
    int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&
                       (red != green || green != blue);
  
    if (ip > 255)
      png_error (image->opaque->png_ptr, "color-map index out of range");
  
    /* Update the cache with whether the file gamma is significantly different
      * from sRGB.
      */
    if (encoding == P_FILE) {
      if (display->file_encoding == P_NOTSET)
        set_file_encoding (display);
  
      /* Note that the cached value may be P_FILE too, but if it is then the
         * gamma_to_linear member has been set.
         */
      encoding = display->file_encoding;
    }
  
    if (encoding == P_FILE) {
      png_fixed_point g = display->gamma_to_linear;
  
      red = png_gamma_16bit_correct (red * 257, g);
      green = png_gamma_16bit_correct (green * 257, g);
      blue = png_gamma_16bit_correct (blue * 257, g);
  
      if (convert_to_Y != 0 || output_encoding == P_LINEAR) {
        alpha *= 257;
        encoding = P_LINEAR;
      }
  
      else {
        red = PNG_sRGB_FROM_LINEAR(red * 255);
        green = PNG_sRGB_FROM_LINEAR(green * 255);
        blue = PNG_sRGB_FROM_LINEAR(blue * 255);
        encoding = P_sRGB;
      }
    }
  
    else if (encoding == P_LINEAR8) {
      /* This encoding occurs quite frequently in test cases because PngSuite
         * includes a gAMA 1.0 chunk with most images.
         */
      red *= 257;
      green *= 257;
      blue *= 257;
      alpha *= 257;
      encoding = P_LINEAR;
    }
  
    else if (encoding == P_sRGB &&
             (convert_to_Y != 0 || output_encoding == P_LINEAR)) {
      /* The values are 8-bit sRGB values, but must be converted to 16-bit
         * linear.
         */
      red = png_sRGB_table[red];
      green = png_sRGB_table[green];
      blue = png_sRGB_table[blue];
      alpha *= 257;
      encoding = P_LINEAR;
    }
  
    /* This is set if the color isn't gray but the output is. */
    if (encoding == P_LINEAR) {
      if (convert_to_Y != 0) {
        /* NOTE: these values are copied from png_do_rgb_to_gray */
        png_uint_32 y = (png_uint_32) 6968 * red + (png_uint_32) 23434 * green +
                        (png_uint_32) 2366 * blue;
  
        if (output_encoding == P_LINEAR)
          y = (y + 16384) >> 15;
  
        else {
          /* y is scaled by 32768, we need it scaled by 255: */
          y = (y + 128) >> 8;
          y *= 255;
          y = PNG_sRGB_FROM_LINEAR((y + 64) >> 7);
          alpha = PNG_DIV257(alpha);
          encoding = P_sRGB;
        }
  
        blue = red = green = y;
      }
  
      else if (output_encoding == P_sRGB) {
        red = PNG_sRGB_FROM_LINEAR(red * 255);
        green = PNG_sRGB_FROM_LINEAR(green * 255);
        blue = PNG_sRGB_FROM_LINEAR(blue * 255);
        alpha = PNG_DIV257(alpha);
        encoding = P_sRGB;
      }
    }
  
    if (encoding != output_encoding)
      png_error (image->opaque->png_ptr, "bad encoding (internal error)");
  
    /* Store the value. */
    {
  #     ifdef PNG_FORMAT_AFIRST_SUPPORTED
      int afirst = (image->format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
                   (image->format & PNG_FORMAT_FLAG_ALPHA) != 0;
  #     else
  #        define afirst 0
  #     endif
  #     ifdef PNG_FORMAT_BGR_SUPPORTED
      int bgr = (image->format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
  #     else
  #        define bgr 0
  #     endif
  
      if (output_encoding == P_LINEAR) {
        png_uint_16p entry = png_voidcast(png_uint_16p, display->colormap);
  
        entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);
  
        /* The linear 16-bit values must be pre-multiplied by the alpha channel
            * value, if less than 65535 (this is, effectively, composite on black
            * if the alpha channel is removed.)
            */
        switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format)) {
          case 4:
            entry[afirst ? 0 : 3] = (png_uint_16) alpha;
            /* FALLTHROUGH */
  
          case 3:
            if (alpha < 65535) {
              if (alpha > 0) {
                blue = (blue * alpha + 32767U) / 65535U;
                green = (green * alpha + 32767U) / 65535U;
                red = (red * alpha + 32767U) / 65535U;
              }
  
              else
                red = green = blue = 0;
            }
            entry[afirst + (2 ^ bgr)] = (png_uint_16) blue;
            entry[afirst + 1] = (png_uint_16) green;
            entry[afirst + bgr] = (png_uint_16) red;
            break;
  
          case 2:
            entry[1 ^ afirst] = (png_uint_16) alpha;
            /* FALLTHROUGH */
  
          case 1:
            if (alpha < 65535) {
              if (alpha > 0)
                green = (green * alpha + 32767U) / 65535U;
  
              else
                green = 0;
            }
            entry[afirst] = (png_uint_16) green;
            break;
  
          default:
            break;
        }
      }
  
      else /* output encoding is P_sRGB */
      {
        png_bytep entry = png_voidcast(png_bytep, display->colormap);
  
        entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);
  
        switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format)) {
          case 4:
            entry[afirst ? 0 : 3] = (png_byte) alpha;
            /* FALLTHROUGH */
          case 3:
            entry[afirst + (2 ^ bgr)] = (png_byte) blue;
            entry[afirst + 1] = (png_byte) green;
            entry[afirst + bgr] = (png_byte) red;
            break;
  
          case 2:
            entry[1 ^ afirst] = (png_byte) alpha;
            /* FALLTHROUGH */
          case 1:
            entry[afirst] = (png_byte) green;
            break;
  
          default:
            break;
        }
      }
  
  #     ifdef afirst
  #        undef afirst
  #     endif
  #     ifdef bgr
  #        undef bgr
  #     endif
    }
  }
  
  static int
  make_gray_file_colormap (png_image_read_control* display) {
    unsigned int i;
  
    for (i = 0; i < 256; ++i)
      png_create_colormap_entry (display, i, i, i, i, 255, P_FILE);
  
    return (int) i;
  }
  
  static int
  make_gray_colormap (png_image_read_control* display) {
    unsigned int i;
  
    for (i = 0; i < 256; ++i)
      png_create_colormap_entry (display, i, i, i, i, 255, P_sRGB);
  
    return (int) i;
  }
  
  #define PNG_GRAY_COLORMAP_ENTRIES 256
  
  static int
  make_ga_colormap (png_image_read_control* display) {
    unsigned int i, a;
  
    /* Alpha is retained, the output will be a color-map with entries
      * selected by six levels of alpha.  One transparent entry, 6 gray
      * levels for all the intermediate alpha values, leaving 230 entries
      * for the opaque grays.  The color-map entries are the six values
      * [0..5]*51, the GA processing uses PNG_DIV51(value) to find the
      * relevant entry.
      *
      * if (alpha > 229) // opaque
      * {
      *    // The 231 entries are selected to make the math below work:
      *    base = 0;
      *    entry = (231 * gray + 128) >> 8;
      * }
      * else if (alpha < 26) // transparent
      * {
      *    base = 231;
      *    entry = 0;
      * }
      * else // partially opaque
      * {
      *    base = 226 + 6 * PNG_DIV51(alpha);
      *    entry = PNG_DIV51(gray);
      * }
      */
    i = 0;
    while (i < 231) {
      unsigned int gray = (i * 256 + 115) / 231;
      png_create_colormap_entry (display, i++, gray, gray, gray, 255, P_sRGB);
    }
  
    /* 255 is used here for the component values for consistency with the code
      * that undoes premultiplication in pngwrite.c.
      */
    png_create_colormap_entry (display, i++, 255, 255, 255, 0, P_sRGB);
  
    for (a = 1; a < 5; ++a) {
      unsigned int g;
  
      for (g = 0; g < 6; ++g)
        png_create_colormap_entry (display, i++, g * 51, g * 51, g * 51, a * 51,
                                   P_sRGB);
    }
  
    return (int) i;
  }
  
  #define PNG_GA_COLORMAP_ENTRIES 256
  
  static int
  make_rgb_colormap (png_image_read_control* display) {
    unsigned int i, r;
  
    /* Build a 6x6x6 opaque RGB cube */
    for (i = r = 0; r < 6; ++r) {
      unsigned int g;
  
      for (g = 0; g < 6; ++g) {
        unsigned int b;
  
        for (b = 0; b < 6; ++b)
          png_create_colormap_entry (display, i++, r * 51, g * 51, b * 51, 255,
                                     P_sRGB);
      }
    }
  
    return (int) i;
  }
  
  #define PNG_RGB_COLORMAP_ENTRIES 216
  
  /* Return a palette index to the above palette given three 8-bit sRGB values. */
  #define PNG_RGB_INDEX(r, g, b) \
     ((png_byte)(6 * (6 * PNG_DIV51(r) + PNG_DIV51(g)) + PNG_DIV51(b)))
  
  static int
  png_image_read_colormap (png_voidp argument) {
    png_image_read_control* display =
        png_voidcast(png_image_read_control*, argument);
    png_imagep image = display->image;
  
    png_structrp png_ptr = image->opaque->png_ptr;
    png_uint_32 output_format = image->format;
    int output_encoding = (output_format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
                          P_LINEAR : P_sRGB;
  
    unsigned int cmap_entries;
    unsigned int output_processing;        /* Output processing option */
    unsigned int data_encoding = P_NOTSET; /* Encoding libpng must produce */
  
    /* Background information; the background color and the index of this color
      * in the color-map if it exists (else 256).
      */
    unsigned int background_index = 256;
    png_uint_32 back_r, back_g, back_b;
  
    /* Flags to accumulate things that need to be done to the input. */
    int expand_tRNS = 0;
  
    /* Exclude the NYI feature of compositing onto a color-mapped buffer; it is
      * very difficult to do, the results look awful, and it is difficult to see
      * what possible use it is because the application can't control the
      * color-map.
      */
    if (((png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0 ||
         png_ptr->num_trans > 0) /* alpha in input */ &&
        ((output_format & PNG_FORMAT_FLAG_ALPHA) == 0) /* no alpha in output */) {
      if (output_encoding == P_LINEAR) /* compose on black */
        back_b = back_g = back_r = 0;
  
      else if (display->background == NULL /* no way to remove it */)
        png_error (png_ptr,
                   "background color must be supplied to remove alpha/transparency");
  
        /* Get a copy of the background color (this avoids repeating the checks
         * below.)  The encoding is 8-bit sRGB or 16-bit linear, depending on the
         * output format.
         */
      else {
        back_g = display->background->green;
        if ((output_format & PNG_FORMAT_FLAG_COLOR) != 0) {
          back_r = display->background->red;
          back_b = display->background->blue;
        }
        else
          back_b = back_r = back_g;
      }
    }
  
    else if (output_encoding == P_LINEAR)
      back_b = back_r = back_g = 65535;
  
    else
      back_b = back_r = back_g = 255;
  
    /* Default the input file gamma if required - this is necessary because
      * libpng assumes that if no gamma information is present the data is in the
      * output format, but the simplified API deduces the gamma from the input
      * format.
      */
    if ((png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_GAMMA) == 0) {
      /* Do this directly, not using the png_colorspace functions, to ensure
         * that it happens even if the colorspace is invalid (though probably if
         * it is the setting will be ignored)  Note that the same thing can be
         * achieved at the application interface with png_set_gAMA.
         */
      if (png_ptr->bit_depth == 16 &&
          (image->flags & PNG_IMAGE_FLAG_16BIT_sRGB) == 0)
        png_ptr->colorspace.gamma = PNG_GAMMA_LINEAR;
  
      else
        png_ptr->colorspace.gamma = PNG_GAMMA_sRGB_INVERSE;
  
      png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
    }
  
    /* Decide what to do based on the PNG color type of the input data.  The
      * utility function png_create_colormap_entry deals with most aspects of the
      * output transformations; this code works out how to produce bytes of
      * color-map entries from the original format.
      */
    switch (png_ptr->color_type) {
      case PNG_COLOR_TYPE_GRAY:
        if (png_ptr->bit_depth <= 8) {
          /* There at most 256 colors in the output, regardless of
               * transparency.
               */
          unsigned int step, i, val, trans = 256/*ignore*/, back_alpha = 0;
  
          cmap_entries = 1U << png_ptr->bit_depth;
          if (cmap_entries > image->colormap_entries)
            png_error (png_ptr, "gray[8] color-map: too few entries");
  
          step = 255 / (cmap_entries - 1);
          output_processing = PNG_CMAP_NONE;
  
          /* If there is a tRNS chunk then this either selects a transparent
               * value or, if the output has no alpha, the background color.
               */
          if (png_ptr->num_trans > 0) {
            trans = png_ptr->trans_color.gray;
  
            if ((output_format & PNG_FORMAT_FLAG_ALPHA) == 0)
              back_alpha = output_encoding == P_LINEAR ? 65535 : 255;
          }
  
          /* png_create_colormap_entry just takes an RGBA and writes the
               * corresponding color-map entry using the format from 'image',
               * including the required conversion to sRGB or linear as
               * appropriate.  The input values are always either sRGB (if the
               * gamma correction flag is 0) or 0..255 scaled file encoded values
               * (if the function must gamma correct them).
               */
          for (i = val = 0; i < cmap_entries; ++i, val += step) {
            /* 'i' is a file value.  While this will result in duplicated
                  * entries for 8-bit non-sRGB encoded files it is necessary to
                  * have non-gamma corrected values to do tRNS handling.
                  */
            if (i != trans)
              png_create_colormap_entry (display, i, val, val, val, 255,
                                         P_FILE/*8-bit with file gamma*/);
  
              /* Else this entry is transparent.  The colors don't matter if
                  * there is an alpha channel (back_alpha == 0), but it does no
                  * harm to pass them in; the values are not set above so this
                  * passes in white.
                  *
                  * NOTE: this preserves the full precision of the application
                  * supplied background color when it is used.
                  */
            else
              png_create_colormap_entry (display, i, back_r, back_g, back_b,
                                         back_alpha, output_encoding);
          }
  
          /* We need libpng to preserve the original encoding. */
          data_encoding = P_FILE;
  
          /* The rows from libpng, while technically gray values, are now also
               * color-map indices; however, they may need to be expanded to 1
               * byte per pixel.  This is what png_set_packing does (i.e., it
               * unpacks the bit values into bytes.)
               */
          if (png_ptr->bit_depth < 8)
            png_set_packing (png_ptr);
        }
  
        else /* bit depth is 16 */
        {
          /* The 16-bit input values can be converted directly to 8-bit gamma
               * encoded values; however, if a tRNS chunk is present 257 color-map
               * entries are required.  This means that the extra entry requires
               * special processing; add an alpha channel, sacrifice gray level
               * 254 and convert transparent (alpha==0) entries to that.
               *
               * Use libpng to chop the data to 8 bits.  Convert it to sRGB at the
               * same time to minimize quality loss.  If a tRNS chunk is present
               * this means libpng must handle it too; otherwise it is impossible
               * to do the exact match on the 16-bit value.
               *
               * If the output has no alpha channel *and* the background color is
               * gray then it is possible to let libpng handle the substitution by
               * ensuring that the corresponding gray level matches the background
               * color exactly.
               */
          data_encoding = P_sRGB;
  
          if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
            png_error (png_ptr, "gray[16] color-map: too few entries");
  
          cmap_entries = (unsigned int) make_gray_colormap (display);
  
          if (png_ptr->num_trans > 0) {
            unsigned int back_alpha;
  
            if ((output_format & PNG_FORMAT_FLAG_ALPHA) != 0)
              back_alpha = 0;
  
            else {
              if (back_r == back_g && back_g == back_b) {
                /* Background is gray; no special processing will be
                        * required.
                        */
                png_color_16 c;
                png_uint_32 gray = back_g;
  
                if (output_encoding == P_LINEAR) {
                  gray = PNG_sRGB_FROM_LINEAR(gray * 255);
  
                  /* And make sure the corresponding palette entry
                           * matches.
                           */
                  png_create_colormap_entry (display, gray, back_g, back_g,
                                             back_g, 65535, P_LINEAR);
                }
  
                /* The background passed to libpng, however, must be the
                        * sRGB value.
                        */
                c.index = 0; /*unused*/
                c.gray = c.red = c.green = c.blue = (png_uint_16) gray;
  
                /* NOTE: does this work without expanding tRNS to alpha?
                        * It should be the color->gray case below apparently
                        * doesn't.
                        */
                png_set_background_fixed (png_ptr, &c,
                                          PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                                          0/*gamma: not used*/);
  
                output_processing = PNG_CMAP_NONE;
                break;
              }
  #ifdef __COVERITY__
                                                                                                                                      /* Coverity claims that output_encoding cannot be 2 (P_LINEAR)
                    * here.
                    */
                    back_alpha = 255;
  #else
              back_alpha = output_encoding == P_LINEAR ? 65535 : 255;
  #endif
            }
  
            /* output_processing means that the libpng-processed row will be
                  * 8-bit GA and it has to be processing to single byte color-map
                  * values.  Entry 254 is replaced by either a completely
                  * transparent entry or by the background color at full
                  * precision (and the background color is not a simple gray
                  * level in this case.)
                  */
            expand_tRNS = 1;
            output_processing = PNG_CMAP_TRANS;
            background_index = 254;
  
            /* And set (overwrite) color-map entry 254 to the actual
                  * background color at full precision.
                  */
            png_create_colormap_entry (display, 254, back_r, back_g, back_b,
                                       back_alpha, output_encoding);
          }
  
          else
            output_processing = PNG_CMAP_NONE;
        }
        break;
  
      case PNG_COLOR_TYPE_GRAY_ALPHA:
        /* 8-bit or 16-bit PNG with two channels - gray and alpha.  A minimum
            * of 65536 combinations.  If, however, the alpha channel is to be
            * removed there are only 256 possibilities if the background is gray.
            * (Otherwise there is a subset of the 65536 possibilities defined by
            * the triangle between black, white and the background color.)
            *
            * Reduce 16-bit files to 8-bit and sRGB encode the result.  No need to
            * worry about tRNS matching - tRNS is ignored if there is an alpha
            * channel.
            */
        data_encoding = P_sRGB;
  
        if ((output_format & PNG_FORMAT_FLAG_ALPHA) != 0) {
          if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
            png_error (png_ptr, "gray+alpha color-map: too few entries");
  
          cmap_entries = (unsigned int) make_ga_colormap (display);
  
          background_index = PNG_CMAP_GA_BACKGROUND;
          output_processing = PNG_CMAP_GA;
        }
  
        else /* alpha is removed */
        {
          /* Alpha must be removed as the PNG data is processed when the
               * background is a color because the G and A channels are
               * independent and the vector addition (non-parallel vectors) is a
               * 2-D problem.
               *
               * This can be reduced to the same algorithm as above by making a
               * colormap containing gray levels (for the opaque grays), a
               * background entry (for a transparent pixel) and a set of four six
               * level color values, one set for each intermediate alpha value.
               * See the comments in make_ga_colormap for how this works in the
               * per-pixel processing.
               *
               * If the background is gray, however, we only need a 256 entry gray
               * level color map.  It is sufficient to make the entry generated
               * for the background color be exactly the color specified.
               */
          if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0 ||
              (back_r == back_g && back_g == back_b)) {
            /* Background is gray; no special processing will be required. */
            png_color_16 c;
            png_uint_32 gray = back_g;
  
            if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
              png_error (png_ptr, "gray-alpha color-map: too few entries");
  
            cmap_entries = (unsigned int) make_gray_colormap (display);
  
            if (output_encoding == P_LINEAR) {
              gray = PNG_sRGB_FROM_LINEAR(gray * 255);
  
              /* And make sure the corresponding palette entry matches. */
              png_create_colormap_entry (display, gray, back_g, back_g,
                                         back_g, 65535, P_LINEAR);
            }
  
            /* The background passed to libpng, however, must be the sRGB
                  * value.
                  */
            c.index = 0; /*unused*/
            c.gray = c.red = c.green = c.blue = (png_uint_16) gray;
  
            png_set_background_fixed (png_ptr, &c,
                                      PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                                      0/*gamma: not used*/);
  
            output_processing = PNG_CMAP_NONE;
          }
  
          else {
            png_uint_32 i, a;
  
            /* This is the same as png_make_ga_colormap, above, except that
                  * the entries are all opaque.
                  */
            if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
              png_error (png_ptr, "ga-alpha color-map: too few entries");
  
            i = 0;
            while (i < 231) {
              png_uint_32 gray = (i * 256 + 115) / 231;
              png_create_colormap_entry (display, i++, gray, gray, gray,
                                         255, P_sRGB);
            }
  
            /* NOTE: this preserves the full precision of the application
                  * background color.
                  */
            background_index = i;
            png_create_colormap_entry (display, i++, back_r, back_g, back_b,
  #ifdef __COVERITY__
                                                                                                                                        /* Coverity claims that output_encoding
                      * cannot be 2 (P_LINEAR) here.
                      */ 255U,
  #else
                                       output_encoding == P_LINEAR ? 65535U : 255U,
  #endif
                                       output_encoding);
  
            /* For non-opaque input composite on the sRGB background - this
                  * requires inverting the encoding for each component.  The input
                  * is still converted to the sRGB encoding because this is a
                  * reasonable approximate to the logarithmic curve of human
                  * visual sensitivity, at least over the narrow range which PNG
                  * represents.  Consequently 'G' is always sRGB encoded, while
                  * 'A' is linear.  We need the linear background colors.
                  */
            if (output_encoding == P_sRGB) /* else already linear */
            {
              /* This may produce a value not exactly matching the
                     * background, but that's ok because these numbers are only
                     * used when alpha != 0
                     */
              back_r = png_sRGB_table[back_r];
              back_g = png_sRGB_table[back_g];
              back_b = png_sRGB_table[back_b];
            }
  
            for (a = 1; a < 5; ++a) {
              unsigned int g;
  
              /* PNG_sRGB_FROM_LINEAR expects a 16-bit linear value scaled
                     * by an 8-bit alpha value (0..255).
                     */
              png_uint_32 alpha = 51 * a;
              png_uint_32 back_rx = (255 - alpha) * back_r;
              png_uint_32 back_gx = (255 - alpha) * back_g;
              png_uint_32 back_bx = (255 - alpha) * back_b;
  
              for (g = 0; g < 6; ++g) {
                png_uint_32 gray = png_sRGB_table[g * 51] * alpha;
  
                png_create_colormap_entry (display, i++,
                                           PNG_sRGB_FROM_LINEAR(gray + back_rx),
                                           PNG_sRGB_FROM_LINEAR(gray + back_gx),
                                           PNG_sRGB_FROM_LINEAR(gray + back_bx), 255, P_sRGB);
              }
            }
  
            cmap_entries = i;
            output_processing = PNG_CMAP_GA;
          }
        }
        break;
  
      case PNG_COLOR_TYPE_RGB:
      case PNG_COLOR_TYPE_RGB_ALPHA:
        /* Exclude the case where the output is gray; we can always handle this
            * with the cases above.
            */
        if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0) {
          /* The color-map will be grayscale, so we may as well convert the
               * input RGB values to a simple grayscale and use the grayscale
               * code above.
               *
               * NOTE: calling this apparently damages the recognition of the
               * transparent color in background color handling; call
               * png_set_tRNS_to_alpha before png_set_background_fixed.
               */
          png_set_rgb_to_gray_fixed (png_ptr, PNG_ERROR_ACTION_NONE, -1,
                                     -1);
          data_encoding = P_sRGB;
  
          /* The output will now be one or two 8-bit gray or gray+alpha
               * channels.  The more complex case arises when the input has alpha.
               */
          if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
               png_ptr->num_trans > 0) &&
              (output_format & PNG_FORMAT_FLAG_ALPHA) != 0) {
            /* Both input and output have an alpha channel, so no background
                  * processing is required; just map the GA bytes to the right
                  * color-map entry.
                  */
            expand_tRNS = 1;
  
            if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
              png_error (png_ptr, "rgb[ga] color-map: too few entries");
  
            cmap_entries = (unsigned int) make_ga_colormap (display);
            background_index = PNG_CMAP_GA_BACKGROUND;
            output_processing = PNG_CMAP_GA;
          }
  
          else {
            /* Either the input or the output has no alpha channel, so there
                  * will be no non-opaque pixels in the color-map; it will just be
                  * grayscale.
                  */
            if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
              png_error (png_ptr, "rgb[gray] color-map: too few entries");
  
            /* Ideally this code would use libpng to do the gamma correction,
                  * but if an input alpha channel is to be removed we will hit the
                  * libpng bug in gamma+compose+rgb-to-gray (the double gamma
                  * correction bug).  Fix this by dropping the gamma correction in
                  * this case and doing it in the palette; this will result in
                  * duplicate palette entries, but that's better than the
                  * alternative of double gamma correction.
                  */
            if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                 png_ptr->num_trans > 0) &&
                png_gamma_not_sRGB (png_ptr->colorspace.gamma) != 0) {
              cmap_entries = (unsigned int) make_gray_file_colormap (display);
              data_encoding = P_FILE;
            }
  
            else
              cmap_entries = (unsigned int) make_gray_colormap (display);
  
            /* But if the input has alpha or transparency it must be removed
                  */
            if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                png_ptr->num_trans > 0) {
              png_color_16 c;
              png_uint_32 gray = back_g;
  
              /* We need to ensure that the application background exists in
                     * the colormap and that completely transparent pixels map to
                     * it.  Achieve this simply by ensuring that the entry
                     * selected for the background really is the background color.
                     */
              if (data_encoding == P_FILE) /* from the fixup above */
              {
                /* The app supplied a gray which is in output_encoding, we
                        * need to convert it to a value of the input (P_FILE)
                        * encoding then set this palette entry to the required
                        * output encoding.
                        */
                if (output_encoding == P_sRGB)
                  gray = png_sRGB_table[gray]; /* now P_LINEAR */
  
                gray = PNG_DIV257(png_gamma_16bit_correct (gray,
                                                           png_ptr->colorspace.gamma)); /* now P_FILE */
  
                /* And make sure the corresponding palette entry contains
                        * exactly the required sRGB value.
                        */
                png_create_colormap_entry (display, gray, back_g, back_g,
                                           back_g, 0/*unused*/, output_encoding);
              }
  
              else if (output_encoding == P_LINEAR) {
                gray = PNG_sRGB_FROM_LINEAR(gray * 255);
  
                /* And make sure the corresponding palette entry matches.
                        */
                png_create_colormap_entry (display, gray, back_g, back_g,
                                           back_g, 0/*unused*/, P_LINEAR);
              }
  
              /* The background passed to libpng, however, must be the
                     * output (normally sRGB) value.
                     */
              c.index = 0; /*unused*/
              c.gray = c.red = c.green = c.blue = (png_uint_16) gray;
  
              /* NOTE: the following is apparently a bug in libpng. Without
                     * it the transparent color recognition in
                     * png_set_background_fixed seems to go wrong.
                     */
              expand_tRNS = 1;
              png_set_background_fixed (png_ptr, &c,
                                        PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                                        0/*gamma: not used*/);
            }
  
            output_processing = PNG_CMAP_NONE;
          }
        }
  
        else /* output is color */
        {
          /* We could use png_quantize here so long as there is no transparent
               * color or alpha; png_quantize ignores alpha.  Easier overall just
               * to do it once and using PNG_DIV51 on the 6x6x6 reduced RGB cube.
               * Consequently we always want libpng to produce sRGB data.
               */
          data_encoding = P_sRGB;
  
          /* Is there any transparency or alpha? */
          if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
              png_ptr->num_trans > 0) {
            /* Is there alpha in the output too?  If so all four channels are
                  * processed into a special RGB cube with alpha support.
                  */
            if ((output_format & PNG_FORMAT_FLAG_ALPHA) != 0) {
              png_uint_32 r;
  
              if (PNG_RGB_COLORMAP_ENTRIES + 1 + 27 > image->colormap_entries)
                png_error (png_ptr, "rgb+alpha color-map: too few entries");
  
              cmap_entries = (unsigned int) make_rgb_colormap (display);
  
              /* Add a transparent entry. */
              png_create_colormap_entry (display, cmap_entries, 255, 255,
                                         255, 0, P_sRGB);
  
              /* This is stored as the background index for the processing
                     * algorithm.
                     */
              background_index = cmap_entries++;
  
              /* Add 27 r,g,b entries each with alpha 0.5. */
              for (r = 0; r < 256; r = (r << 1) | 0x7f) {
                png_uint_32 g;
  
                for (g = 0; g < 256; g = (g << 1) | 0x7f) {
                  png_uint_32 b;
  
                  /* This generates components with the values 0, 127 and
                           * 255
                           */
                  for (b = 0; b < 256; b = (b << 1) | 0x7f)
                    png_create_colormap_entry (display, cmap_entries++,
                                               r, g, b, 128, P_sRGB);
                }
              }
  
              expand_tRNS = 1;
              output_processing = PNG_CMAP_RGB_ALPHA;
            }
  
            else {
              /* Alpha/transparency must be removed.  The background must
                     * exist in the color map (achieved by setting adding it after
                     * the 666 color-map).  If the standard processing code will
                     * pick up this entry automatically that's all that is
                     * required; libpng can be called to do the background
                     * processing.
                     */
              unsigned int sample_size =
                  PNG_IMAGE_SAMPLE_SIZE(output_format);
              png_uint_32 r, g, b; /* sRGB background */
  
              if (PNG_RGB_COLORMAP_ENTRIES + 1 + 27 > image->colormap_entries)
                png_error (png_ptr, "rgb-alpha color-map: too few entries");
  
              cmap_entries = (unsigned int) make_rgb_colormap (display);
  
              png_create_colormap_entry (display, cmap_entries, back_r,
                                         back_g, back_b, 0/*unused*/, output_encoding);
  
              if (output_encoding == P_LINEAR) {
                r = PNG_sRGB_FROM_LINEAR(back_r * 255);
                g = PNG_sRGB_FROM_LINEAR(back_g * 255);
                b = PNG_sRGB_FROM_LINEAR(back_b * 255);
              }
  
              else {
                r = back_r;
                g = back_g;
                b = back_g;
              }
  
              /* Compare the newly-created color-map entry with the one the
                     * PNG_CMAP_RGB algorithm will use.  If the two entries don't
                     * match, add the new one and set this as the background
                     * index.
                     */
              if (memcmp ((png_const_bytep) display->colormap +
                          sample_size * cmap_entries,
                          (png_const_bytep) display->colormap +
                          sample_size * PNG_RGB_INDEX(r, g, b),
                          sample_size) != 0) {
                /* The background color must be added. */
                background_index = cmap_entries++;
  
                /* Add 27 r,g,b entries each with created by composing with
                        * the background at alpha 0.5.
                        */
                for (r = 0; r < 256; r = (r << 1) | 0x7f) {
                  for (g = 0; g < 256; g = (g << 1) | 0x7f) {
                    /* This generates components with the values 0, 127
                              * and 255
                              */
                    for (b = 0; b < 256; b = (b << 1) | 0x7f)
                      png_create_colormap_entry (display, cmap_entries++,
                                                 png_colormap_compose (display, r, P_sRGB, 128,
                                                                       back_r, output_encoding),
                                                 png_colormap_compose (display, g, P_sRGB, 128,
                                                                       back_g, output_encoding),
                                                 png_colormap_compose (display, b, P_sRGB, 128,
                                                                       back_b, output_encoding),
                                                 0/*unused*/, output_encoding);
                  }
                }
  
                expand_tRNS = 1;
                output_processing = PNG_CMAP_RGB_ALPHA;
              }
  
              else /* background color is in the standard color-map */
              {
                png_color_16 c;
  
                c.index = 0; /*unused*/
                c.red = (png_uint_16) back_r;
                c.gray = c.green = (png_uint_16) back_g;
                c.blue = (png_uint_16) back_b;
  
                png_set_background_fixed (png_ptr, &c,
                                          PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                                          0/*gamma: not used*/);
  
                output_processing = PNG_CMAP_RGB;
              }
            }
          }
  
          else /* no alpha or transparency in the input */
          {
            /* Alpha in the output is irrelevant, simply map the opaque input
                  * pixels to the 6x6x6 color-map.
                  */
            if (PNG_RGB_COLORMAP_ENTRIES > image->colormap_entries)
              png_error (png_ptr, "rgb color-map: too few entries");
  
            cmap_entries = (unsigned int) make_rgb_colormap (display);
            output_processing = PNG_CMAP_RGB;
          }
        }
        break;
  
      case PNG_COLOR_TYPE_PALETTE:
        /* It's already got a color-map.  It may be necessary to eliminate the
            * tRNS entries though.
            */
      {
        unsigned int num_trans = png_ptr->num_trans;
        png_const_bytep trans = num_trans > 0 ? png_ptr->trans_alpha : NULL;
        png_const_colorp colormap = png_ptr->palette;
        int do_background = trans != NULL &&
                            (output_format & PNG_FORMAT_FLAG_ALPHA) == 0;
        unsigned int i;
  
        /* Just in case: */
        if (trans == NULL)
          num_trans = 0;
  
        output_processing = PNG_CMAP_NONE;
        data_encoding = P_FILE; /* Don't change from color-map indices */
        cmap_entries = (unsigned int) png_ptr->num_palette;
        if (cmap_entries > 256)
          cmap_entries = 256;
  
        if (cmap_entries > (unsigned int) image->colormap_entries)
          png_error (png_ptr, "palette color-map: too few entries");
  
        for (i = 0; i < cmap_entries; ++i) {
          if (do_background != 0 && i < num_trans && trans[i] < 255) {
            if (trans[i] == 0)
              png_create_colormap_entry (display, i, back_r, back_g,
                                         back_b, 0, output_encoding);
  
            else {
              /* Must compose the PNG file color in the color-map entry
                        * on the sRGB color in 'back'.
                        */
              png_create_colormap_entry (display, i,
                                         png_colormap_compose (display, colormap[i].red,
                                                               P_FILE, trans[i], back_r, output_encoding),
                                         png_colormap_compose (display, colormap[i].green,
                                                               P_FILE, trans[i], back_g, output_encoding),
                                         png_colormap_compose (display, colormap[i].blue,
                                                               P_FILE, trans[i], back_b, output_encoding),
                                         output_encoding == P_LINEAR ? trans[i] * 257U :
                                         trans[i],
                                         output_encoding);
            }
          }
  
          else
            png_create_colormap_entry (display, i, colormap[i].red,
                                       colormap[i].green, colormap[i].blue,
                                       i < num_trans ? trans[i] : 255U, P_FILE/*8-bit*/);
        }
  
        /* The PNG data may have indices packed in fewer than 8 bits, it
               * must be expanded if so.
               */
        if (png_ptr->bit_depth < 8)
          png_set_packing (png_ptr);
      }
        break;
  
      default:
        png_error (png_ptr, "invalid PNG color type");
        /*NOT REACHED*/
    }
  
    /* Now deal with the output processing */
    if (expand_tRNS != 0 && png_ptr->num_trans > 0 &&
        (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) == 0)
      png_set_tRNS_to_alpha (png_ptr);
  
    switch (data_encoding) {
      case P_sRGB:
        /* Change to 8-bit sRGB */
        png_set_alpha_mode_fixed (png_ptr, PNG_ALPHA_PNG, PNG_GAMMA_sRGB);
        /* FALLTHROUGH */
  
      case P_FILE:
        if (png_ptr->bit_depth > 8)
          png_set_scale_16 (png_ptr);
        break;
  
  #ifdef __GNUC__
      default:
        png_error (png_ptr, "bad data option (internal error)");
  #endif
    }
  
    if (cmap_entries > 256 || cmap_entries > image->colormap_entries)
      png_error (png_ptr, "color map overflow (BAD internal error)");
  
    image->colormap_entries = cmap_entries;
  
    /* Double check using the recorded background index */
    switch (output_processing) {
      case PNG_CMAP_NONE:
        if (background_index != PNG_CMAP_NONE_BACKGROUND)
          goto bad_background;
        break;
  
      case PNG_CMAP_GA:
        if (background_index != PNG_CMAP_GA_BACKGROUND)
          goto bad_background;
        break;
  
      case PNG_CMAP_TRANS:
        if (background_index >= cmap_entries ||
            background_index != PNG_CMAP_TRANS_BACKGROUND)
          goto bad_background;
        break;
  
      case PNG_CMAP_RGB:
        if (background_index != PNG_CMAP_RGB_BACKGROUND)
          goto bad_background;
        break;
  
      case PNG_CMAP_RGB_ALPHA:
        if (background_index != PNG_CMAP_RGB_ALPHA_BACKGROUND)
          goto bad_background;
        break;
  
      default:
        png_error (png_ptr, "bad processing option (internal error)");
  
      bad_background:
        png_error (png_ptr, "bad background index (internal error)");
    }
  
    display->colormap_processing = (int) output_processing;
  
    return 1/*ok*/;
  }
  
  /* The final part of the color-map read called from png_image_finish_read. */
  static int
  png_image_read_and_map (png_voidp argument) {
    png_image_read_control* display = png_voidcast(png_image_read_control*,
                                                   argument);
    png_imagep image = display->image;
    png_structrp png_ptr = image->opaque->png_ptr;
    int passes;
  
    /* Called when the libpng data must be transformed into the color-mapped
      * form.  There is a local row buffer in display->local and this routine must
      * do the interlace handling.
      */
    switch (png_ptr->interlaced) {
      case PNG_INTERLACE_NONE:
        passes = 1;
        break;
  
      case PNG_INTERLACE_ADAM7:
        passes = PNG_INTERLACE_ADAM7_PASSES;
        break;
  
      default:
        png_error (png_ptr, "unknown interlace type");
    }
  
    {
      png_uint_32 height = image->height;
      png_uint_32 width = image->width;
      int proc = display->colormap_processing;
      png_bytep first_row = png_voidcast(png_bytep, display->first_row);
      ptrdiff_t step_row = display->row_bytes;
      int pass;
  
      for (pass = 0; pass < passes; ++pass) {
        unsigned int startx, stepx, stepy;
        png_uint_32 y;
  
        if (png_ptr->interlaced == PNG_INTERLACE_ADAM7) {
          /* The row may be empty for a short image: */
          if (PNG_PASS_COLS(width, pass) == 0)
            continue;
  
          startx = PNG_PASS_START_COL(pass);
          stepx = PNG_PASS_COL_OFFSET(pass);
          y = PNG_PASS_START_ROW(pass);
          stepy = PNG_PASS_ROW_OFFSET(pass);
        }
  
        else {
          y = 0;
          startx = 0;
          stepx = stepy = 1;
        }
  
        for (; y < height; y += stepy) {
          png_bytep inrow = png_voidcast(png_bytep, display->local_row);
          png_bytep outrow = first_row + y * step_row;
          png_const_bytep end_row = outrow + width;
  
          /* Read read the libpng data into the temporary buffer. */
          png_read_row (png_ptr, inrow, NULL);
  
          /* Now process the row according to the processing option, note
               * that the caller verifies that the format of the libpng output
               * data is as required.
               */
          outrow += startx;
          switch (proc) {
            case PNG_CMAP_GA:
              for (; outrow < end_row; outrow += stepx) {
                /* The data is always in the PNG order */
                unsigned int gray = *inrow++;
                unsigned int alpha = *inrow++;
                unsigned int entry;
  
                /* NOTE: this code is copied as a comment in
                        * make_ga_colormap above.  Please update the
                        * comment if you change this code!
                        */
                if (alpha > 229) /* opaque */
                {
                  entry = (231 * gray + 128) >> 8;
                }
                else if (alpha < 26) /* transparent */
                {
                  entry = 231;
                }
                else /* partially opaque */
                {
                  entry = 226 + 6 * PNG_DIV51(alpha) + PNG_DIV51(gray);
                }
  
                *outrow = (png_byte) entry;
              }
              break;
  
            case PNG_CMAP_TRANS:
              for (; outrow < end_row; outrow += stepx) {
                png_byte gray = *inrow++;
                png_byte alpha = *inrow++;
  
                if (alpha == 0)
                  *outrow = PNG_CMAP_TRANS_BACKGROUND;
  
                else if (gray != PNG_CMAP_TRANS_BACKGROUND)
                  *outrow = gray;
  
                else
                  *outrow = (png_byte) (PNG_CMAP_TRANS_BACKGROUND + 1);
              }
              break;
  
            case PNG_CMAP_RGB:
              for (; outrow < end_row; outrow += stepx) {
                *outrow = PNG_RGB_INDEX(inrow[0], inrow[1], inrow[2]);
                inrow += 3;
              }
              break;
  
            case PNG_CMAP_RGB_ALPHA:
              for (; outrow < end_row; outrow += stepx) {
                unsigned int alpha = inrow[3];
  
                /* Because the alpha entries only hold alpha==0.5 values
                        * split the processing at alpha==0.25 (64) and 0.75
                        * (196).
                        */
  
                if (alpha >= 196)
                  *outrow = PNG_RGB_INDEX(inrow[0], inrow[1],
                                          inrow[2]);
  
                else if (alpha < 64)
                  *outrow = PNG_CMAP_RGB_ALPHA_BACKGROUND;
  
                else {
                  /* Likewise there are three entries for each of r, g
                           * and b.  We could select the entry by popcount on
                           * the top two bits on those architectures that
                           * support it, this is what the code below does,
                           * crudely.
                           */
                  unsigned int back_i = PNG_CMAP_RGB_ALPHA_BACKGROUND + 1;
  
                  /* Here are how the values map:
                           *
                           * 0x00 .. 0x3f -> 0
                           * 0x40 .. 0xbf -> 1
                           * 0xc0 .. 0xff -> 2
                           *
                           * So, as above with the explicit alpha checks, the
                           * breakpoints are at 64 and 196.
                           */
                  if (inrow[0] & 0x80)
                    back_i += 9; /* red */
                  if (inrow[0] & 0x40)
                    back_i += 9;
                  if (inrow[0] & 0x80)
                    back_i += 3; /* green */
                  if (inrow[0] & 0x40)
                    back_i += 3;
                  if (inrow[0] & 0x80)
                    back_i += 1; /* blue */
                  if (inrow[0] & 0x40)
                    back_i += 1;
  
                  *outrow = (png_byte) back_i;
                }
  
                inrow += 4;
              }
              break;
  
            default:
              break;
          }
        }
      }
    }
  
    return 1;
  }
  
  static int
  png_image_read_colormapped (png_voidp argument) {
    png_image_read_control* display = png_voidcast(png_image_read_control*,
                                                   argument);
    png_imagep image = display->image;
    png_controlp control = image->opaque;
    png_structrp png_ptr = control->png_ptr;
    png_inforp info_ptr = control->info_ptr;
  
    int passes = 0; /* As a flag */
  
    PNG_SKIP_CHUNKS(png_ptr);
  
    /* Update the 'info' structure and make sure the result is as required; first
      * make sure to turn on the interlace handling if it will be required
      * (because it can't be turned on *after* the call to png_read_update_info!)
      */
    if (display->colormap_processing == PNG_CMAP_NONE)
      passes = png_set_interlace_handling (png_ptr);
  
    png_read_update_info (png_ptr, info_ptr);
  
    /* The expected output can be deduced from the colormap_processing option. */
    switch (display->colormap_processing) {
      case PNG_CMAP_NONE:
        /* Output must be one channel and one byte per pixel, the output
            * encoding can be anything.
            */
        if ((info_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
             info_ptr->color_type == PNG_COLOR_TYPE_GRAY) &&
            info_ptr->bit_depth == 8)
          break;
  
        goto bad_output;
  
      case PNG_CMAP_TRANS:
      case PNG_CMAP_GA:
        /* Output must be two channels and the 'G' one must be sRGB, the latter
            * can be checked with an exact number because it should have been set
            * to this number above!
            */
        if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA &&
            info_ptr->bit_depth == 8 &&
            png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
            image->colormap_entries == 256)
          break;
  
        goto bad_output;
  
      case PNG_CMAP_RGB:
        /* Output must be 8-bit sRGB encoded RGB */
        if (info_ptr->color_type == PNG_COLOR_TYPE_RGB &&
            info_ptr->bit_depth == 8 &&
            png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
            image->colormap_entries == 216)
          break;
  
        goto bad_output;
  
      case PNG_CMAP_RGB_ALPHA:
        /* Output must be 8-bit sRGB encoded RGBA */
        if (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
            info_ptr->bit_depth == 8 &&
            png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
            image->colormap_entries == 244 /* 216 + 1 + 27 */)
          break;
  
        goto bad_output;
  
      default:
      bad_output:
        png_error (png_ptr, "bad color-map processing (internal error)");
    }
  
    /* Now read the rows.  Do this here if it is possible to read directly into
      * the output buffer, otherwise allocate a local row buffer of the maximum
      * size libpng requires and call the relevant processing routine safely.
      */
    {
      png_voidp first_row = display->buffer;
      ptrdiff_t row_bytes = display->row_stride;
  
      /* The following expression is designed to work correctly whether it gives
         * a signed or an unsigned result.
         */
      if (row_bytes < 0) {
        char* ptr = png_voidcast(char*, first_row);
        ptr += (image->height - 1) * (-row_bytes);
        first_row = png_voidcast(png_voidp, ptr);
      }
  
      display->first_row = first_row;
      display->row_bytes = row_bytes;
    }
  
    if (passes == 0) {
      int result;
      png_voidp row = png_malloc (png_ptr, png_get_rowbytes (png_ptr, info_ptr));
  
      display->local_row = row;
      result = png_safe_execute (image, png_image_read_and_map, display);
      display->local_row = NULL;
      png_free (png_ptr, row);
  
      return result;
    }
  
    else {
      png_alloc_size_t row_bytes = (png_alloc_size_t) display->row_bytes;
  
      while (--passes >= 0) {
        png_uint_32 y = image->height;
        png_bytep row = png_voidcast(png_bytep, display->first_row);
  
        for (; y > 0; --y) {
          png_read_row (png_ptr, row, NULL);
          row += row_bytes;
        }
      }
  
      return 1;
    }
  }
  
  /* Just the row reading part of png_image_read. */
  static int
  png_image_read_composite (png_voidp argument) {
    png_image_read_control* display = png_voidcast(png_image_read_control*,
                                                   argument);
    png_imagep image = display->image;
    png_structrp png_ptr = image->opaque->png_ptr;
    int passes;
  
    switch (png_ptr->interlaced) {
      case PNG_INTERLACE_NONE:
        passes = 1;
        break;
  
      case PNG_INTERLACE_ADAM7:
        passes = PNG_INTERLACE_ADAM7_PASSES;
        break;
  
      default:
        png_error (png_ptr, "unknown interlace type");
    }
  
    {
      png_uint_32 height = image->height;
      png_uint_32 width = image->width;
      ptrdiff_t step_row = display->row_bytes;
      unsigned int channels =
          (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ? 3 : 1;
      int pass;
  
      for (pass = 0; pass < passes; ++pass) {
        unsigned int startx, stepx, stepy;
        png_uint_32 y;
  
        if (png_ptr->interlaced == PNG_INTERLACE_ADAM7) {
          /* The row may be empty for a short image: */
          if (PNG_PASS_COLS(width, pass) == 0)
            continue;
  
          startx = PNG_PASS_START_COL(pass) * channels;
          stepx = PNG_PASS_COL_OFFSET(pass) * channels;
          y = PNG_PASS_START_ROW(pass);
          stepy = PNG_PASS_ROW_OFFSET(pass);
        }
  
        else {
          y = 0;
          startx = 0;
          stepx = channels;
          stepy = 1;
        }
  
        for (; y < height; y += stepy) {
          png_bytep inrow = png_voidcast(png_bytep, display->local_row);
          png_bytep outrow;
          png_const_bytep end_row;
  
          /* Read the row, which is packed: */
          png_read_row (png_ptr, inrow, NULL);
  
          outrow = png_voidcast(png_bytep, display->first_row);
          outrow += y * step_row;
          end_row = outrow + width * channels;
  
          /* Now do the composition on each pixel in this row. */
          outrow += startx;
          for (; outrow < end_row; outrow += stepx) {
            png_byte alpha = inrow[channels];
  
            if (alpha > 0) /* else no change to the output */
            {
              unsigned int c;
  
              for (c = 0; c < channels; ++c) {
                png_uint_32 component = inrow[c];
  
                if (alpha < 255) /* else just use component */
                {
                  /* This is PNG_OPTIMIZED_ALPHA, the component value
                           * is a linear 8-bit value.  Combine this with the
                           * current outrow[c] value which is sRGB encoded.
                           * Arithmetic here is 16-bits to preserve the output
                           * values correctly.
                           */
                  component *= 257 * 255; /* =65535 */
                  component += (255 - alpha) * png_sRGB_table[outrow[c]];
  
                  /* So 'component' is scaled by 255*65535 and is
                           * therefore appropriate for the sRGB to linear
                           * conversion table.
                           */
                  component = PNG_sRGB_FROM_LINEAR(component);
                }
  
                outrow[c] = (png_byte) component;
              }
            }
  
            inrow += channels + 1; /* components and alpha channel */
          }
        }
      }
    }
  
    return 1;
  }
  
  /* The do_local_background case; called when all the following transforms are to
   * be done:
   *
   * PNG_RGB_TO_GRAY
   * PNG_COMPOSITE
   * PNG_GAMMA
   *
   * This is a work-around for the fact that both the PNG_RGB_TO_GRAY and
   * PNG_COMPOSITE code performs gamma correction, so we get double gamma
   * correction.  The fix-up is to prevent the PNG_COMPOSITE operation from
   * happening inside libpng, so this routine sees an 8 or 16-bit gray+alpha
   * row and handles the removal or pre-multiplication of the alpha channel.
   */
  static int
  png_image_read_background (png_voidp argument) {
    png_image_read_control* display = png_voidcast(png_image_read_control*,
                                                   argument);
    png_imagep image = display->image;
    png_structrp png_ptr = image->opaque->png_ptr;
    png_inforp info_ptr = image->opaque->info_ptr;
    png_uint_32 height = image->height;
    png_uint_32 width = image->width;
    int pass, passes;
  
    /* Double check the convoluted logic below.  We expect to get here with
      * libpng doing rgb to gray and gamma correction but background processing
      * left to the png_image_read_background function.  The rows libpng produce
      * might be 8 or 16-bit but should always have two channels; gray plus alpha.
      */
    if ((png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
      png_error (png_ptr, "lost rgb to gray");
  
    if ((png_ptr->transformations & PNG_COMPOSE) != 0)
      png_error (png_ptr, "unexpected compose");
  
    if (png_get_channels (png_ptr, info_ptr) != 2)
      png_error (png_ptr, "lost/gained channels");
  
    /* Expect the 8-bit case to always remove the alpha channel */
    if ((image->format & PNG_FORMAT_FLAG_LINEAR) == 0 &&
        (image->format & PNG_FORMAT_FLAG_ALPHA) != 0)
      png_error (png_ptr, "unexpected 8-bit transformation");
  
    switch (png_ptr->interlaced) {
      case PNG_INTERLACE_NONE:
        passes = 1;
        break;
  
      case PNG_INTERLACE_ADAM7:
        passes = PNG_INTERLACE_ADAM7_PASSES;
        break;
  
      default:
        png_error (png_ptr, "unknown interlace type");
    }
  
    /* Use direct access to info_ptr here because otherwise the simplified API
      * would require PNG_EASY_ACCESS_SUPPORTED (just for this.)  Note this is
      * checking the value after libpng expansions, not the original value in the
      * PNG.
      */
    switch (info_ptr->bit_depth) {
      case 8:
        /* 8-bit sRGB gray values with an alpha channel; the alpha channel is
            * to be removed by composing on a background: either the row if
            * display->background is NULL or display->background->green if not.
            * Unlike the code above ALPHA_OPTIMIZED has *not* been done.
            */
      {
        png_bytep first_row = png_voidcast(png_bytep, display->first_row);
        ptrdiff_t step_row = display->row_bytes;
  
        for (pass = 0; pass < passes; ++pass) {
          png_bytep row = png_voidcast(png_bytep, display->first_row);
          unsigned int startx, stepx, stepy;
          png_uint_32 y;
  
          if (png_ptr->interlaced == PNG_INTERLACE_ADAM7) {
            /* The row may be empty for a short image: */
            if (PNG_PASS_COLS(width, pass) == 0)
              continue;
  
            startx = PNG_PASS_START_COL(pass);
            stepx = PNG_PASS_COL_OFFSET(pass);
            y = PNG_PASS_START_ROW(pass);
            stepy = PNG_PASS_ROW_OFFSET(pass);
          }
  
          else {
            y = 0;
            startx = 0;
            stepx = stepy = 1;
          }
  
          if (display->background == NULL) {
            for (; y < height; y += stepy) {
              png_bytep inrow = png_voidcast(png_bytep,
                                             display->local_row);
              png_bytep outrow = first_row + y * step_row;
              png_const_bytep end_row = outrow + width;
  
              /* Read the row, which is packed: */
              png_read_row (png_ptr, inrow, NULL);
  
              /* Now do the composition on each pixel in this row. */
              outrow += startx;
              for (; outrow < end_row; outrow += stepx) {
                png_byte alpha = inrow[1];
  
                if (alpha > 0) /* else no change to the output */
                {
                  png_uint_32 component = inrow[0];
  
                  if (alpha < 255) /* else just use component */
                  {
                    /* Since PNG_OPTIMIZED_ALPHA was not set it is
                                 * necessary to invert the sRGB transfer
                                 * function and multiply the alpha out.
                                 */
                    component = png_sRGB_table[component] * alpha;
                    component += png_sRGB_table[outrow[0]] *
                                 (255 - alpha);
                    component = PNG_sRGB_FROM_LINEAR(component);
                  }
  
                  outrow[0] = (png_byte) component;
                }
  
                inrow += 2; /* gray and alpha channel */
              }
            }
          }
  
          else /* constant background value */
          {
            png_byte background8 = display->background->green;
            png_uint_16 background = png_sRGB_table[background8];
  
            for (; y < height; y += stepy) {
              png_bytep inrow = png_voidcast(png_bytep,
                                             display->local_row);
              png_bytep outrow = first_row + y * step_row;
              png_const_bytep end_row = outrow + width;
  
              /* Read the row, which is packed: */
              png_read_row (png_ptr, inrow, NULL);
  
              /* Now do the composition on each pixel in this row. */
              outrow += startx;
              for (; outrow < end_row; outrow += stepx) {
                png_byte alpha = inrow[1];
  
                if (alpha > 0) /* else use background */
                {
                  png_uint_32 component = inrow[0];
  
                  if (alpha < 255) /* else just use component */
                  {
                    component = png_sRGB_table[component] * alpha;
                    component += background * (255 - alpha);
                    component = PNG_sRGB_FROM_LINEAR(component);
                  }
  
                  outrow[0] = (png_byte) component;
                }
  
                else
                  outrow[0] = background8;
  
                inrow += 2; /* gray and alpha channel */
              }
  
              row += display->row_bytes;
            }
          }
        }
      }
        break;
  
      case 16:
        /* 16-bit linear with pre-multiplied alpha; the pre-multiplication must
            * still be done and, maybe, the alpha channel removed.  This code also
            * handles the alpha-first option.
            */
      {
        png_uint_16p first_row = png_voidcast(png_uint_16p,
                                              display->first_row);
        /* The division by two is safe because the caller passed in a
               * stride which was multiplied by 2 (below) to get row_bytes.
               */
        ptrdiff_t step_row = display->row_bytes / 2;
        unsigned int preserve_alpha = (image->format &
                                       PNG_FORMAT_FLAG_ALPHA) != 0;
        unsigned int outchannels = 1U + preserve_alpha;
        int swap_alpha = 0;
  
  #           ifdef PNG_SIMPLIFIED_READ_AFIRST_SUPPORTED
        if (preserve_alpha != 0 &&
            (image->format & PNG_FORMAT_FLAG_AFIRST) != 0)
          swap_alpha = 1;
  #           endif
  
        for (pass = 0; pass < passes; ++pass) {
          unsigned int startx, stepx, stepy;
          png_uint_32 y;
  
          /* The 'x' start and step are adjusted to output components here.
                  */
          if (png_ptr->interlaced == PNG_INTERLACE_ADAM7) {
            /* The row may be empty for a short image: */
            if (PNG_PASS_COLS(width, pass) == 0)
              continue;
  
            startx = PNG_PASS_START_COL(pass) * outchannels;
            stepx = PNG_PASS_COL_OFFSET(pass) * outchannels;
            y = PNG_PASS_START_ROW(pass);
            stepy = PNG_PASS_ROW_OFFSET(pass);
          }
  
          else {
            y = 0;
            startx = 0;
            stepx = outchannels;
            stepy = 1;
          }
  
          for (; y < height; y += stepy) {
            png_const_uint_16p inrow;
            png_uint_16p outrow = first_row + y * step_row;
            png_uint_16p end_row = outrow + width * outchannels;
  
            /* Read the row, which is packed: */
            png_read_row (png_ptr, png_voidcast(png_bytep,
                                                display->local_row), NULL);
            inrow = png_voidcast(png_const_uint_16p, display->local_row);
  
            /* Now do the pre-multiplication on each pixel in this row.
                     */
            outrow += startx;
            for (; outrow < end_row; outrow += stepx) {
              png_uint_32 component = inrow[0];
              png_uint_16 alpha = inrow[1];
  
              if (alpha > 0) /* else 0 */
              {
                if (alpha < 65535) /* else just use component */
                {
                  component *= alpha;
                  component += 32767;
                  component /= 65535;
                }
              }
  
              else
                component = 0;
  
              outrow[swap_alpha] = (png_uint_16) component;
              if (preserve_alpha != 0)
                outrow[1 ^ swap_alpha] = alpha;
  
              inrow += 2; /* components and alpha channel */
            }
          }
        }
      }
        break;
  
  #ifdef __GNUC__
      default:
        png_error (png_ptr, "unexpected bit depth");
  #endif
    }
  
    return 1;
  }
  
  /* The guts of png_image_finish_read as a png_safe_execute callback. */
  static int
  png_image_read_direct (png_voidp argument) {
    png_image_read_control* display = png_voidcast(png_image_read_control*,
                                                   argument);
    png_imagep image = display->image;
    png_structrp png_ptr = image->opaque->png_ptr;
    png_inforp info_ptr = image->opaque->info_ptr;
  
    png_uint_32 format = image->format;
    int linear = (format & PNG_FORMAT_FLAG_LINEAR) != 0;
    int do_local_compose = 0;
    int do_local_background = 0; /* to avoid double gamma correction bug */
    int passes = 0;
  
    /* Add transforms to ensure the correct output format is produced then check
      * that the required implementation support is there.  Always expand; always
      * need 8 bits minimum, no palette and expanded tRNS.
      */
    png_set_expand (png_ptr);
  
    /* Now check the format to see if it was modified. */
    {
      png_uint_32 base_format = png_image_format (png_ptr) &
                                ~PNG_FORMAT_FLAG_COLORMAP /* removed by png_set_expand */;
      png_uint_32 change = format ^ base_format;
      png_fixed_point output_gamma;
      int mode; /* alpha mode */
  
      /* Do this first so that we have a record if rgb to gray is happening. */
      if ((change & PNG_FORMAT_FLAG_COLOR) != 0) {
        /* gray<->color transformation required. */
        if ((format & PNG_FORMAT_FLAG_COLOR) != 0)
          png_set_gray_to_rgb (png_ptr);
  
        else {
          /* libpng can't do both rgb to gray and
               * background/pre-multiplication if there is also significant gamma
               * correction, because both operations require linear colors and
               * the code only supports one transform doing the gamma correction.
               * Handle this by doing the pre-multiplication or background
               * operation in this code, if necessary.
               *
               * TODO: fix this by rewriting pngrtran.c (!)
               *
               * For the moment (given that fixing this in pngrtran.c is an
               * enormous change) 'do_local_background' is used to indicate that
               * the problem exists.
               */
          if ((base_format & PNG_FORMAT_FLAG_ALPHA) != 0)
            do_local_background = 1/*maybe*/;
  
          png_set_rgb_to_gray_fixed (png_ptr, PNG_ERROR_ACTION_NONE,
                                     PNG_RGB_TO_GRAY_DEFAULT, PNG_RGB_TO_GRAY_DEFAULT);
        }
  
        change &= ~PNG_FORMAT_FLAG_COLOR;
      }
  
      /* Set the gamma appropriately, linear for 16-bit input, sRGB otherwise.
         */
      {
        png_fixed_point input_gamma_default;
  
        if ((base_format & PNG_FORMAT_FLAG_LINEAR) != 0 &&
            (image->flags & PNG_IMAGE_FLAG_16BIT_sRGB) == 0)
          input_gamma_default = PNG_GAMMA_LINEAR;
        else
          input_gamma_default = PNG_DEFAULT_sRGB;
  
        /* Call png_set_alpha_mode to set the default for the input gamma; the
            * output gamma is set by a second call below.
            */
        png_set_alpha_mode_fixed (png_ptr, PNG_ALPHA_PNG, input_gamma_default);
      }
  
      if (linear != 0) {
        /* If there *is* an alpha channel in the input it must be multiplied
            * out; use PNG_ALPHA_STANDARD, otherwise just use PNG_ALPHA_PNG.
            */
        if ((base_format & PNG_FORMAT_FLAG_ALPHA) != 0)
          mode = PNG_ALPHA_STANDARD; /* associated alpha */
  
        else
          mode = PNG_ALPHA_PNG;
  
        output_gamma = PNG_GAMMA_LINEAR;
      }
  
      else {
        mode = PNG_ALPHA_PNG;
        output_gamma = PNG_DEFAULT_sRGB;
      }
  
      if ((change & PNG_FORMAT_FLAG_ASSOCIATED_ALPHA) != 0) {
        mode = PNG_ALPHA_OPTIMIZED;
        change &= ~PNG_FORMAT_FLAG_ASSOCIATED_ALPHA;
      }
  
      /* If 'do_local_background' is set check for the presence of gamma
         * correction; this is part of the work-round for the libpng bug
         * described above.
         *
         * TODO: fix libpng and remove this.
         */
      if (do_local_background != 0) {
        png_fixed_point gtest;
  
        /* This is 'png_gamma_threshold' from pngrtran.c; the test used for
            * gamma correction, the screen gamma hasn't been set on png_struct
            * yet; it's set below.  png_struct::gamma, however, is set to the
            * final value.
            */
        if (png_muldiv (&gtest, output_gamma, png_ptr->colorspace.gamma,
                        PNG_FP_1) != 0 && png_gamma_significant (gtest) == 0)
          do_local_background = 0;
  
        else if (mode == PNG_ALPHA_STANDARD) {
          do_local_background = 2/*required*/;
          mode = PNG_ALPHA_PNG; /* prevent libpng doing it */
        }
  
        /* else leave as 1 for the checks below */
      }
  
      /* If the bit-depth changes then handle that here. */
      if ((change & PNG_FORMAT_FLAG_LINEAR) != 0) {
        if (linear != 0 /*16-bit output*/)
          png_set_expand_16 (png_ptr);
  
        else /* 8-bit output */
          png_set_scale_16 (png_ptr);
  
        change &= ~PNG_FORMAT_FLAG_LINEAR;
      }
  
      /* Now the background/alpha channel changes. */
      if ((change & PNG_FORMAT_FLAG_ALPHA) != 0) {
        /* Removing an alpha channel requires composition for the 8-bit
            * formats; for the 16-bit it is already done, above, by the
            * pre-multiplication and the channel just needs to be stripped.
            */
        if ((base_format & PNG_FORMAT_FLAG_ALPHA) != 0) {
          /* If RGB->gray is happening the alpha channel must be left and the
               * operation completed locally.
               *
               * TODO: fix libpng and remove this.
               */
          if (do_local_background != 0)
            do_local_background = 2/*required*/;
  
            /* 16-bit output: just remove the channel */
          else if (linear != 0) /* compose on black (well, pre-multiply) */
            png_set_strip_alpha (png_ptr);
  
            /* 8-bit output: do an appropriate compose */
          else if (display->background != NULL) {
            png_color_16 c;
  
            c.index = 0; /*unused*/
            c.red = display->background->red;
            c.green = display->background->green;
            c.blue = display->background->blue;
            c.gray = display->background->green;
  
            /* This is always an 8-bit sRGB value, using the 'green' channel
                  * for gray is much better than calculating the luminance here;
                  * we can get off-by-one errors in that calculation relative to
                  * the app expectations and that will show up in transparent
                  * pixels.
                  */
            png_set_background_fixed (png_ptr, &c,
                                      PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                                      0/*gamma: not used*/);
          }
  
          else /* compose on row: implemented below. */
          {
            do_local_compose = 1;
            /* This leaves the alpha channel in the output, so it has to be
                  * removed by the code below.  Set the encoding to the 'OPTIMIZE'
                  * one so the code only has to hack on the pixels that require
                  * composition.
                  */
            mode = PNG_ALPHA_OPTIMIZED;
          }
        }
  
        else /* output needs an alpha channel */
        {
          /* This is tricky because it happens before the swap operation has
               * been accomplished; however, the swap does *not* swap the added
               * alpha channel (weird API), so it must be added in the correct
               * place.
               */
          png_uint_32 filler; /* opaque filler */
          int where;
  
          if (linear != 0)
            filler = 65535;
  
          else
            filler = 255;
  
  #ifdef PNG_FORMAT_AFIRST_SUPPORTED
          if ((format & PNG_FORMAT_FLAG_AFIRST) != 0) {
            where = PNG_FILLER_BEFORE;
            change &= ~PNG_FORMAT_FLAG_AFIRST;
          }
  
          else
  #endif
            where = PNG_FILLER_AFTER;
  
          png_set_add_alpha (png_ptr, filler, where);
        }
  
        /* This stops the (irrelevant) call to swap_alpha below. */
        change &= ~PNG_FORMAT_FLAG_ALPHA;
      }
  
      /* Now set the alpha mode correctly; this is always done, even if there is
         * no alpha channel in either the input or the output because it correctly
         * sets the output gamma.
         */
      png_set_alpha_mode_fixed (png_ptr, mode, output_gamma);
  
  #     ifdef PNG_FORMAT_BGR_SUPPORTED
      if ((change & PNG_FORMAT_FLAG_BGR) != 0) {
        /* Check only the output format; PNG is never BGR; don't do this if
               * the output is gray, but fix up the 'format' value in that case.
               */
        if ((format & PNG_FORMAT_FLAG_COLOR) != 0)
          png_set_bgr (png_ptr);
  
        else
          format &= ~PNG_FORMAT_FLAG_BGR;
  
        change &= ~PNG_FORMAT_FLAG_BGR;
      }
  #     endif
  
  #     ifdef PNG_FORMAT_AFIRST_SUPPORTED
      if ((change & PNG_FORMAT_FLAG_AFIRST) != 0) {
        /* Only relevant if there is an alpha channel - it's particularly
               * important to handle this correctly because do_local_compose may
               * be set above and then libpng will keep the alpha channel for this
               * code to remove.
               */
        if ((format & PNG_FORMAT_FLAG_ALPHA) != 0) {
          /* Disable this if doing a local background,
                  * TODO: remove this when local background is no longer required.
                  */
          if (do_local_background != 2)
            png_set_swap_alpha (png_ptr);
        }
  
        else
          format &= ~PNG_FORMAT_FLAG_AFIRST;
  
        change &= ~PNG_FORMAT_FLAG_AFIRST;
      }
  #     endif
  
      /* If the *output* is 16-bit then we need to check for a byte-swap on this
         * architecture.
         */
      if (linear != 0) {
        png_uint_16 le = 0x0001;
  
        if ((*(png_const_bytep) &le) != 0)
          png_set_swap (png_ptr);
      }
  
      /* If change is not now 0 some transformation is missing - error out. */
      if (change != 0)
        png_error (png_ptr, "png_read_image: unsupported transformation");
    }
  
    PNG_SKIP_CHUNKS(png_ptr);
  
    /* Update the 'info' structure and make sure the result is as required; first
      * make sure to turn on the interlace handling if it will be required
      * (because it can't be turned on *after* the call to png_read_update_info!)
      *
      * TODO: remove the do_local_background fixup below.
      */
    if (do_local_compose == 0 && do_local_background != 2)
      passes = png_set_interlace_handling (png_ptr);
  
    png_read_update_info (png_ptr, info_ptr);
  
    {
      png_uint_32 info_format = 0;
  
      if ((info_ptr->color_type & PNG_COLOR_MASK_COLOR) != 0)
        info_format |= PNG_FORMAT_FLAG_COLOR;
  
      if ((info_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0) {
        /* do_local_compose removes this channel below. */
        if (do_local_compose == 0) {
          /* do_local_background does the same if required. */
          if (do_local_background != 2 ||
              (format & PNG_FORMAT_FLAG_ALPHA) != 0)
            info_format |= PNG_FORMAT_FLAG_ALPHA;
        }
      }
  
      else if (do_local_compose != 0) /* internal error */
        png_error (png_ptr, "png_image_read: alpha channel lost");
  
      if ((format & PNG_FORMAT_FLAG_ASSOCIATED_ALPHA) != 0) {
        info_format |= PNG_FORMAT_FLAG_ASSOCIATED_ALPHA;
      }
  
      if (info_ptr->bit_depth == 16)
        info_format |= PNG_FORMAT_FLAG_LINEAR;
  
  #ifdef PNG_FORMAT_BGR_SUPPORTED
      if ((png_ptr->transformations & PNG_BGR) != 0)
        info_format |= PNG_FORMAT_FLAG_BGR;
  #endif
  
  #ifdef PNG_FORMAT_AFIRST_SUPPORTED
      if (do_local_background == 2) {
        if ((format & PNG_FORMAT_FLAG_AFIRST) != 0)
          info_format |= PNG_FORMAT_FLAG_AFIRST;
      }
  
      if ((png_ptr->transformations & PNG_SWAP_ALPHA) != 0 ||
          ((png_ptr->transformations & PNG_ADD_ALPHA) != 0 &&
           (png_ptr->flags & PNG_FLAG_FILLER_AFTER) == 0)) {
        if (do_local_background == 2)
          png_error (png_ptr, "unexpected alpha swap transformation");
  
        info_format |= PNG_FORMAT_FLAG_AFIRST;
      }
  #     endif
  
      /* This is actually an internal error. */
      if (info_format != format)
        png_error (png_ptr, "png_read_image: invalid transformations");
    }
  
    /* Now read the rows.  If do_local_compose is set then it is necessary to use
      * a local row buffer.  The output will be GA, RGBA or BGRA and must be
      * converted to G, RGB or BGR as appropriate.  The 'local_row' member of the
      * display acts as a flag.
      */
    {
      png_voidp first_row = display->buffer;
      ptrdiff_t row_bytes = display->row_stride;
  
      if (linear != 0)
        row_bytes *= 2;
  
      /* The following expression is designed to work correctly whether it gives
         * a signed or an unsigned result.
         */
      if (row_bytes < 0) {
        char* ptr = png_voidcast(char*, first_row);
        ptr += (image->height - 1) * (-row_bytes);
        first_row = png_voidcast(png_voidp, ptr);
      }
  
      display->first_row = first_row;
      display->row_bytes = row_bytes;
    }
  
    if (do_local_compose != 0) {
      int result;
      png_voidp row = png_malloc (png_ptr, png_get_rowbytes (png_ptr, info_ptr));
  
      display->local_row = row;
      result = png_safe_execute (image, png_image_read_composite, display);
      display->local_row = NULL;
      png_free (png_ptr, row);
  
      return result;
    }
  
    else if (do_local_background == 2) {
      int result;
      png_voidp row = png_malloc (png_ptr, png_get_rowbytes (png_ptr, info_ptr));
  
      display->local_row = row;
      result = png_safe_execute (image, png_image_read_background, display);
      display->local_row = NULL;
      png_free (png_ptr, row);
  
      return result;
    }
  
    else {
      png_alloc_size_t row_bytes = (png_alloc_size_t) display->row_bytes;
  
      while (--passes >= 0) {
        png_uint_32 y = image->height;
        png_bytep row = png_voidcast(png_bytep, display->first_row);
  
        for (; y > 0; --y) {
          png_read_row (png_ptr, row, NULL);
          row += row_bytes;
        }
      }
  
      return 1;
    }
  }
  
  int PNGAPI
  png_image_finish_read (png_imagep image, png_const_colorp background,
                         void* buffer, png_int_32 row_stride, void* colormap) {
    if (image != NULL && image->version == PNG_IMAGE_VERSION) {
      /* Check for row_stride overflow.  This check is not performed on the
         * original PNG format because it may not occur in the output PNG format
         * and libpng deals with the issues of reading the original.
         */
      unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
  
      /* The following checks just the 'row_stride' calculation to ensure it
         * fits in a signed 32-bit value.  Because channels/components can be
         * either 1 or 2 bytes in size the length of a row can still overflow 32
         * bits; this is just to verify that the 'row_stride' argument can be
         * represented.
         */
      if (image->width <= 0x7fffffffU / channels) /* no overflow */
      {
        png_uint_32 check;
        png_uint_32 png_row_stride = image->width * channels;
  
        if (row_stride == 0)
          row_stride = (png_int_32)/*SAFE*/png_row_stride;
  
        if (row_stride < 0)
          check = (png_uint_32) (-row_stride);
  
        else
          check = (png_uint_32) row_stride;
  
        /* This verifies 'check', the absolute value of the actual stride
            * passed in and detects overflow in the application calculation (i.e.
            * if the app did actually pass in a non-zero 'row_stride'.
            */
        if (image->opaque != NULL && buffer != NULL && check >= png_row_stride) {
          /* Now check for overflow of the image buffer calculation; this
               * limits the whole image size to 32 bits for API compatibility with
               * the current, 32-bit, PNG_IMAGE_BUFFER_SIZE macro.
               *
               * The PNG_IMAGE_BUFFER_SIZE macro is:
               *
               *    (PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)*height*(row_stride))
               *
               * And the component size is always 1 or 2, so make sure that the
               * number of *bytes* that the application is saying are available
               * does actually fit into a 32-bit number.
               *
               * NOTE: this will be changed in 1.7 because PNG_IMAGE_BUFFER_SIZE
               * will be changed to use png_alloc_size_t; bigger images can be
               * accommodated on 64-bit systems.
               */
          if (image->height <=
              0xffffffffU / PNG_IMAGE_PIXEL_COMPONENT_SIZE(image->format) / check) {
            if ((image->format & PNG_FORMAT_FLAG_COLORMAP) == 0 ||
                (image->colormap_entries > 0 && colormap != NULL)) {
              int result;
              png_image_read_control display;
  
              memset (&display, 0, (sizeof display));
              display.image = image;
              display.buffer = buffer;
              display.row_stride = row_stride;
              display.colormap = colormap;
              display.background = background;
              display.local_row = NULL;
  
              /* Choose the correct 'end' routine; for the color-map case
                     * all the setup has already been done.
                     */
              if ((image->format & PNG_FORMAT_FLAG_COLORMAP) != 0)
                result =
                    png_safe_execute (image,
                                      png_image_read_colormap, &display) &&
                    png_safe_execute (image,
                                      png_image_read_colormapped, &display);
  
              else
                result =
                    png_safe_execute (image,
                                      png_image_read_direct, &display);
  
              png_image_free (image);
              return result;
            }
  
            else
              return png_image_error (image,
                                      "png_image_finish_read[color-map]: no color-map");
          }
  
          else
            return png_image_error (image,
                                    "png_image_finish_read: image too large");
        }
  
        else
          return png_image_error (image,
                                  "png_image_finish_read: invalid argument");
      }
  
      else
        return png_image_error (image,
                                "png_image_finish_read: row_stride too large");
    }
  
    else if (image != NULL)
      return png_image_error (image,
                              "png_image_finish_read: damaged PNG_IMAGE_VERSION");
  
    return 0;
  }
  
  #endif /* SIMPLIFIED_READ */
  #endif /* READ */
  