
/* pngrutil.c - utilities to read a png file

   libpng 1.0 beta 4 - version 0.90
   For conditions of distribution and use, see copyright notice in png.h
   Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
   January 10, 1997
   */

#define PNG_INTERNAL
#include "png.h"

/* grab an uint 32 from a buffer */
png_uint_32
png_get_uint_32(png_bytep buf)
{
   png_uint_32 i;

   i = ((png_uint_32)(*buf) << 24) +
      ((png_uint_32)(*(buf + 1)) << 16) +
      ((png_uint_32)(*(buf + 2)) << 8) +
      (png_uint_32)(*(buf + 3));

   return i;
}

/* grab an uint 16 from a buffer */
png_uint_16
png_get_uint_16(png_bytep buf)
{
   png_uint_16 i;

   i = (png_uint_16)(((png_uint_16)(*buf) << 8) +
      (png_uint_16)(*(buf + 1)));

   return i;
}

/* Set the action on getting a CRC error for an ancillary or critical chunk. */
void
png_set_crc_action(png_structp png_ptr, int crit_action, int ancil_action)
{
   /* Tell libpng how we react to CRC errors in critical chunks */
   switch (crit_action)
   {
      case PNG_CRC_NO_CHANGE:                        /* leave setting as is */
         break;
      case PNG_CRC_WARN_USE:                               /* warn/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
         break;
      case PNG_CRC_QUIET_USE:                             /* quiet/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
                           PNG_FLAG_CRC_CRITICAL_IGNORE;
         break;
      case PNG_CRC_WARN_DISCARD:    /* not a valid action for critical data */
         png_warning(png_ptr, "Can't discard critical data on CRC error.");
      case PNG_CRC_ERROR_QUIT:                                /* error/quit */
      case PNG_CRC_DEFAULT:
      default:
         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
         break;
   }

   switch (ancil_action)
   {
      case PNG_CRC_NO_CHANGE:                       /* leave setting as is */
         break;
      case PNG_CRC_WARN_USE:                              /* warn/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
         break;
      case PNG_CRC_QUIET_USE:                            /* quiet/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
                           PNG_FLAG_CRC_ANCILLARY_NOWARN;
         break;
      case PNG_CRC_ERROR_QUIT:                               /* error/quit */
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
         break;
      case PNG_CRC_WARN_DISCARD:                      /* warn/discard data */
      case PNG_CRC_DEFAULT:
      default:
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         break;
   }
}

/* Read data, and (optionally) run it through the CRC. */
void
png_crc_read(png_structp png_ptr, png_bytep buf, png_uint_32 length)
{
   int need_crc = 1;

   if (png_ptr->chunk_name[0] & 0x20)                    /* ancillary */
   {
      if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_MASK) ==
          (PNG_FLAG_CRC_ANCILLARY_USE | PNG_FLAG_CRC_ANCILLARY_NOWARN))
         need_crc = 0;
   }
   else                                                   /* critical */
   {
      if (png_ptr->flags & PNG_FLAG_CRC_CRITICAL_IGNORE)
         need_crc = 0;
   }

   png_read_data(png_ptr, buf, length);

   if (need_crc)
      png_calculate_crc(png_ptr, buf, length);
}

/* Optionally skip data and then check the CRC.  Depending on whether we
   are reading a ancillary or critical chunk, and how the program has set
   things up, we may calculate the CRC on the data and print a message. */
int
png_crc_finish(png_structp png_ptr, png_uint_32 skip)
{
   int need_crc = 1;
   int crc_error;
   png_uint_32 i;

   if (png_ptr->chunk_name[0] & 0x20)                     /* ancillary */
   {
      if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_MASK) ==
          (PNG_FLAG_CRC_ANCILLARY_USE | PNG_FLAG_CRC_ANCILLARY_NOWARN))
         need_crc = 0;
   }
   else                                                    /* critical */
   {
      if (png_ptr->flags & PNG_FLAG_CRC_CRITICAL_IGNORE)
         need_crc = 0;
   }

   for (i = skip; i > png_ptr->zbuf_size; i -= png_ptr->zbuf_size)
   {
      png_read_data(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
      if (need_crc)
         png_calculate_crc(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
   }
   if (i)
   {
      png_read_data(png_ptr, png_ptr->zbuf, i);
      if (need_crc)
         png_calculate_crc(png_ptr, png_ptr->zbuf, i);
   }

   crc_error = png_crc_error(png_ptr);

   if (need_crc && crc_error)
   {
      char msg[80];

      sprintf(msg,"CRC error in %s", png_ptr->chunk_name);

      if ((png_ptr->chunk_name[0] & 0x20 &&                /* Ancillary */
           !(png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN)) ||
          (!(png_ptr->chunk_name[0] & 0x20) &&             /* Critical  */
           png_ptr->flags & PNG_FLAG_CRC_CRITICAL_USE))
      {
         png_warning(png_ptr, msg);
      }
      else
      {
         png_error(png_ptr, msg);
      }
      return 1;
   }

   return 0;
}

/* Compare the CRC stored in the PNG file with that calulated by libpng from
   the data it has read thus far. */
int
png_crc_error(png_structp png_ptr)
{
   png_byte crc_bytes[4];
   png_uint_32 crc;

   png_read_data(png_ptr, crc_bytes, 4);

   crc = png_get_uint_32(crc_bytes);

#ifdef PNG_USE_OWN_CRC
   return (((crc^0xffffffffL) & 0xffffffffL) != (png_ptr->crc & 0xffffffffL));
#else
   return (crc != png_ptr->crc);
#endif
}


/* read and check the IDHR chunk */
void
png_handle_IHDR(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_byte buf[13];
   png_uint_32 width, height;
   int bit_depth, color_type, compression_type, filter_type;
   int interlace_type;

   if (png_ptr->mode != PNG_BEFORE_IHDR)
      png_error(png_ptr, "Out of place IHDR");

   /* check the length */
   if (length != 13)
      png_error(png_ptr, "Invalid IHDR chunk");

   png_ptr->mode |= PNG_HAVE_IHDR;

   png_crc_read(png_ptr, buf, 13);
   png_crc_finish(png_ptr, 0);

   width = png_get_uint_32(buf);
   height = png_get_uint_32(buf + 4);
   bit_depth = buf[8];
   color_type = buf[9];
   compression_type = buf[10];
   filter_type = buf[11];
   interlace_type = buf[12];

   /* check for width and height valid values */
   if (width == 0 || width > 2147483647 || height == 0 || height > 2147483647)
      png_error(png_ptr, "Invalid image size in IHDR");

   /* check other values */
   if (bit_depth != 1 && bit_depth != 2 &&
      bit_depth != 4 && bit_depth != 8 &&
      bit_depth != 16)
      png_error(png_ptr, "Invalid bit depth in IHDR");

   if (color_type < 0 || color_type == 1 ||
      color_type == 5 || color_type > 6)
      png_error(png_ptr, "Invalid color type in IHDR");

   if ((color_type == PNG_COLOR_TYPE_PALETTE && bit_depth) > 8 ||
       ((color_type == PNG_COLOR_TYPE_RGB ||
         color_type == PNG_COLOR_TYPE_GRAY_ALPHA ||
         color_type == PNG_COLOR_TYPE_RGB_ALPHA) && bit_depth < 8))
      png_error(png_ptr, "Invalid color type/bit depth combination in IHDR");

   if (interlace_type > 1)
      png_error(png_ptr, "Unknown interlace method in IHDR");

   if (compression_type > 0)
      png_error(png_ptr, "Unknown compression method in IHDR");

   if (filter_type > 0)
      png_error(png_ptr, "Unknown filter method in IHDR");

   /* set internal variables */
   png_ptr->width = width;
   png_ptr->height = height;
   png_ptr->bit_depth = (png_byte)bit_depth;
   png_ptr->interlaced = (png_byte)interlace_type;
   png_ptr->color_type = (png_byte)color_type;

   /* find number of channels */
   switch (png_ptr->color_type)
   {
      case 0:
      case 3:
         png_ptr->channels = 1;
         break;
      case 2:
         png_ptr->channels = 3;
         break;
      case 4:
         png_ptr->channels = 2;
         break;
      case 6:
         png_ptr->channels = 4;
         break;
   }

   /* set up other useful info */
   png_ptr->pixel_depth = (png_byte)(png_ptr->bit_depth *
      png_ptr->channels);
   png_ptr->rowbytes = ((png_ptr->width *
      (png_uint_32)png_ptr->pixel_depth + 7) >> 3);
   png_read_IHDR(png_ptr, info_ptr, width, height, bit_depth,
      color_type, compression_type, filter_type, interlace_type);
}

/* read and check the palette */
void
png_handle_PLTE(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_colorp palette;
   int num, i;

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before PLTE");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid PLTE after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (png_ptr->mode & PNG_HAVE_PLTE)
      png_error(png_ptr, "Duplicate PLTE chunk");

   png_ptr->mode |= PNG_HAVE_PLTE;

#if !defined(PNG_READ_OPT_PLTE_SUPPORTED)
   if (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
   {
      png_crc_finish(png_ptr, length);
      return;
   }
#endif

   if (length % 3)
   {
      if (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
      {
         png_warning(png_ptr, "Invalid palette chunk");
         png_crc_finish(png_ptr, length);
         return;
      }
      else
      {
         png_error(png_ptr, "Invalid palette chunk");
      }
   }

   num = (int)length / 3;
   palette = (png_colorp)png_malloc(png_ptr, num * sizeof (png_color));
   png_ptr->flags |= PNG_FLAG_FREE_PALETTE;
   for (i = 0; i < num; i++)
   {
      png_byte buf[3];

      png_crc_read(png_ptr, buf, 3);
      /* don't depend upon png_color being any order */
      palette[i].red = buf[0];
      palette[i].green = buf[1];
      palette[i].blue = buf[2];
   }

   /* If we actually NEED the PLTE chunk (ie for a paletted image), we do
      whatever the normal CRC configuration tells us.  However, if we
      have an RGB image, the PLTE can be considered ancillary, so
      we will act as though it is. */
   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
   {
      if (png_crc_finish(png_ptr, 0))
         return;
   }
   else if (png_crc_error(png_ptr))  /* Only if we have a CRC error */
   {
      char msg[80];

      sprintf(msg,"CRC error in %s", png_ptr->chunk_name);

      /* If we don't want to use the data from an ancillary chunk,
         we have two options: an error abort, or a warning and we
         ignore the data in this chunk (which should be OK, since
         it's considered ancillary for a RGB or RGBA image). */
      if (!(png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_USE))
      {
         if (png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN)
         {
            png_error(png_ptr, msg);
         }
         else
         {
            png_warning(png_ptr, msg);
            return;
         }
      }
      else if (!(png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN))
      {
         png_warning(png_ptr, msg);
      }
   }

   png_ptr->palette = palette;
   png_ptr->num_palette = (png_uint_16)num;
   png_read_PLTE(png_ptr, info_ptr, palette, num);
}

void
png_handle_IEND(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   if (!(png_ptr->mode & PNG_HAVE_IHDR) || !(png_ptr->mode & PNG_HAVE_IDAT))
   {
      png_error(png_ptr, "No image in file");
   }

   png_ptr->mode |= PNG_AFTER_IDAT | PNG_HAVE_IEND;

   if (length != 0)
   {
      png_warning(png_ptr, "Incorrect IEND chunk length");
      png_crc_finish(png_ptr, length);
   }
}

#if defined(PNG_READ_gAMA_SUPPORTED)
void
png_handle_gAMA(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_uint_32 igamma;
   float gamma;
   png_byte buf[4];

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before gAMA");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid gAMA after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (png_ptr->mode & PNG_HAVE_PLTE)
      /* Should be an error, but we can cope with it */
      png_warning(png_ptr, "Out of place gAMA chunk");
   else if (info_ptr && info_ptr->valid & PNG_INFO_gAMA)
   {
      png_warning(png_ptr, "Duplicate gAMA chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (length != 4)
   {
      png_warning(png_ptr, "Incorrect gAMA chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, 4);
   if (png_crc_finish(png_ptr, 0))
      return;

   igamma = png_get_uint_32(buf);
   /* check for zero gamma */
   if (!igamma)
      return;

   gamma = (float)igamma / (float)100000.0;
   png_ptr->gamma = gamma;
   png_read_gAMA(png_ptr, info_ptr, gamma);
}
#endif

#if defined(PNG_READ_sBIT_SUPPORTED)
void
png_handle_sBIT(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_uint_32 truelen;
   png_byte buf[4];

   buf[0] = buf[1] = buf[2] = buf[3] = 0;

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before sBIT");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid sBIT after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (png_ptr->mode & PNG_HAVE_PLTE)
      /* Should be an error, but we can cope with it */
      png_warning(png_ptr, "Out of place sBIT chunk");
   else if (info_ptr && info_ptr->valid & PNG_INFO_sBIT)
   {
      png_warning(png_ptr, "Duplicate sBIT chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      truelen = 3;
   else
      truelen = png_ptr->channels;

   if (length != truelen)
   {
      png_warning(png_ptr, "Incorrect sBIT chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, length);
   if (png_crc_finish(png_ptr, 0))
      return;

   if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
   {
      png_ptr->sig_bit.red = buf[0];
      png_ptr->sig_bit.green = buf[1];
      png_ptr->sig_bit.blue = buf[2];
      png_ptr->sig_bit.alpha = buf[3];
   }
   else
   {
      png_ptr->sig_bit.gray = buf[0];
      png_ptr->sig_bit.alpha = buf[1];
   }
   png_read_sBIT(png_ptr, info_ptr, &(png_ptr->sig_bit));
}
#endif

#if defined(PNG_READ_cHRM_SUPPORTED)
void
png_handle_cHRM(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_byte buf[4];
   png_uint_32 val;
   float white_x, white_y, red_x, red_y, green_x, green_y, blue_x, blue_y;

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before sBIT");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid cHRM after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (png_ptr->mode & PNG_HAVE_PLTE)
      /* Should be an error, but we can cope with it */
      png_warning(png_ptr, "Missing PLTE before cHRM");
   else if (info_ptr && info_ptr->valid & PNG_INFO_cHRM)
   {
      png_warning(png_ptr, "Duplicate cHRM chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (length != 32)
   {
      png_warning(png_ptr, "Incorrect cHRM chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, 4);
   val = png_get_uint_32(buf);
   white_x = (float)val / (float)100000.0;

   png_crc_read(png_ptr, buf, 4);
   val = png_get_uint_32(buf);
   white_y = (float)val / (float)100000.0;

   if (white_x < 0 || white_x > 0.8 || white_y < 0 || white_y > 0.8 ||
       white_x + white_y > 1.0)
   {
      png_warning(png_ptr, "Invalid cHRM white point");
      png_crc_finish(png_ptr, 24);
      return;
   }

   png_crc_read(png_ptr, buf, 4);
   val = png_get_uint_32(buf);
   red_x = (float)val / (float)100000.0;

   png_crc_read(png_ptr, buf, 4);
   val = png_get_uint_32(buf);
   red_y = (float)val / (float)100000.0;

   if (red_x < 0 || red_x > 0.8 || red_y < 0 || red_y > 0.8 ||
       red_x + red_y > 1.0)
   {
      png_warning(png_ptr, "Invalid cHRM red point");
      png_crc_finish(png_ptr, 16);
      return;
   }

   png_crc_read(png_ptr, buf, 4);
   val = png_get_uint_32(buf);
   green_x = (float)val / (float)100000.0;

   png_crc_read(png_ptr, buf, 4);
   val = png_get_uint_32(buf);
   green_y = (float)val / (float)100000.0;

   if (green_x < 0 || green_x > 0.8 || green_y < 0 || green_y > 0.8 ||
       green_x + green_y > 1.0)
   {
      png_warning(png_ptr, "Invalid cHRM green point");
      png_crc_finish(png_ptr, 8);
      return;
   }

   png_crc_read(png_ptr, buf, 4);
   val = png_get_uint_32(buf);
   blue_x = (float)val / (float)100000.0;

   png_crc_read(png_ptr, buf, 4);
   val = png_get_uint_32(buf);
   blue_y = (float)val / (float)100000.0;

   if (blue_x < 0 || blue_x > 0.8 || blue_y < 0 || blue_y > 0.8 ||
       blue_x + blue_y > 1.0)
   {
      png_warning(png_ptr, "Invalid cHRM blue point");
      png_crc_finish(png_ptr, 0);
      return;
   }

   if (png_crc_finish(png_ptr, 0))
      return;

   png_read_cHRM(png_ptr, info_ptr,
      white_x, white_y, red_x, red_y, green_x, green_y, blue_x, blue_y);
}
#endif

#if defined(PNG_READ_tRNS_SUPPORTED)
void
png_handle_tRNS(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before tRNS");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid tRNS after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (info_ptr && info_ptr->valid & PNG_INFO_tRNS)
   {
      png_warning(png_ptr, "Duplcate tRNS chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
   {
      if (!(png_ptr->mode & PNG_HAVE_PLTE))
      {
         /* Should be an error, but we can cope with it */
         png_warning(png_ptr, "Missing PLTE before tRNS");
      }
      else if (length > png_ptr->num_palette)
      {
         png_warning(png_ptr, "Incorrect tRNS chunk length");
         png_crc_finish(png_ptr, length);
         return;
      }

      png_ptr->trans = (png_bytep)png_malloc(png_ptr, length);
      png_ptr->flags |= PNG_FLAG_FREE_TRANS;
      png_crc_read(png_ptr, png_ptr->trans, length);
      png_ptr->num_trans = (png_uint_16)length;
   }
   else if (png_ptr->color_type == PNG_COLOR_TYPE_RGB)
   {
      png_byte buf[6];

      if (length != 6)
      {
         png_warning(png_ptr, "Incorrect tRNS chunk length");
         png_crc_finish(png_ptr, length);
         return;
      }

      png_crc_read(png_ptr, buf, length);
      png_ptr->num_trans = 3;
      png_ptr->trans_values.red = png_get_uint_16(buf);
      png_ptr->trans_values.green = png_get_uint_16(buf + 2);
      png_ptr->trans_values.blue = png_get_uint_16(buf + 4);
   }
   else if (png_ptr->color_type == PNG_COLOR_TYPE_GRAY)
   {
      png_byte buf[6];

      if (length != 2)
      {
         png_warning(png_ptr, "Incorrect tRNS chunk length");
         png_crc_finish(png_ptr, length);
         return;
      }

      png_crc_read(png_ptr, buf, 2);
      png_ptr->num_trans = 1;
      png_ptr->trans_values.gray = png_get_uint_16(buf);
   }
   else
   {
      png_warning(png_ptr, "tRNS chunk not allowed with alpha channel");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (png_crc_finish(png_ptr, 0))
      return;

   png_read_tRNS(png_ptr, info_ptr, png_ptr->trans, png_ptr->num_trans,
      &(png_ptr->trans_values));
}
#endif

#if defined(PNG_READ_bKGD_SUPPORTED)
void
png_handle_bKGD(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_uint_32 truelen;
   png_byte buf[6];

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before bKGD");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid bKGD after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
            !(png_ptr->mode & PNG_HAVE_PLTE))
   {
      png_warning(png_ptr, "Missing PLTE before bKGD");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (info_ptr && info_ptr->valid & PNG_INFO_bKGD)
   {
      png_warning(png_ptr, "Duplicate bKGD chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      truelen = 1;
   else if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
      truelen = 6;
   else
      truelen = 2;

   if (length != truelen)
   {
      png_warning(png_ptr, "Incorrect bKGD chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, length);
   if (png_crc_finish(png_ptr, 0))
      return;

   /* We convert the index value into RGB components so that we can allow
    * arbitrary RGB values for background when we have transparency, and
    * so it is easy to determine the RGB values of the background color
    * from the info_ptr struct. */
   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
   {
      png_ptr->background.index = buf[0];
      png_ptr->background.red = (png_uint_16)png_ptr->palette[buf[0]].red;
      png_ptr->background.green = (png_uint_16)png_ptr->palette[buf[0]].green;
      png_ptr->background.blue = (png_uint_16)png_ptr->palette[buf[0]].blue;
   }
   else if (!(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
   {
      png_ptr->background.red =
      png_ptr->background.green =
      png_ptr->background.blue =
      png_ptr->background.gray = png_get_uint_16(buf);
   }
   else
   {
      png_ptr->background.red = png_get_uint_16(buf);
      png_ptr->background.green = png_get_uint_16(buf + 2);
      png_ptr->background.blue = png_get_uint_16(buf + 4);
   }

   png_read_bKGD(png_ptr, info_ptr, &(png_ptr->background));
}
#endif

#if defined(PNG_READ_hIST_SUPPORTED)
void
png_handle_hIST(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   int num, i;

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before hIST");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid hIST after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (!(png_ptr->mode & PNG_HAVE_PLTE))
   {
      png_warning(png_ptr, "Missing PLTE before hIST");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (info_ptr && info_ptr->valid & PNG_INFO_hIST)
   {
      png_warning(png_ptr, "Duplicate hIST chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (length != 2 * png_ptr->num_palette)
   {
      png_warning(png_ptr, "Incorrect hIST chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   num = (int)length / 2;
   png_ptr->hist = (png_uint_16p)png_malloc(png_ptr,
      num * sizeof (png_uint_16));
   png_ptr->flags |= PNG_FLAG_FREE_HIST;
   for (i = 0; i < num; i++)
   {
      png_byte buf[2];

      png_crc_read(png_ptr, buf, 2);
      png_ptr->hist[i] = png_get_uint_16(buf);
   }

   if (png_crc_finish(png_ptr, 0))
      return;

   png_read_hIST(png_ptr, info_ptr, png_ptr->hist);
}
#endif

#if defined(PNG_READ_pHYs_SUPPORTED)
void
png_handle_pHYs(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_byte buf[9];
   png_uint_32 res_x, res_y;
   int unit_type;

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before pHYS");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid pHYS after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (info_ptr && info_ptr->valid & PNG_INFO_pHYs)
   {
      png_warning(png_ptr, "Duplicate pHYS chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (length != 9)
   {
      png_warning(png_ptr, "Incorrect pHYs chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, 9);
   if (png_crc_finish(png_ptr, 0))
      return;

   res_x = png_get_uint_32(buf);
   res_y = png_get_uint_32(buf + 4);
   unit_type = buf[8];
   png_read_pHYs(png_ptr, info_ptr, res_x, res_y, unit_type);
}
#endif

#if defined(PNG_READ_oFFs_SUPPORTED)
void
png_handle_oFFs(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_byte buf[9];
   png_uint_32 offset_x, offset_y;
   int unit_type;

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before oFFs");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid oFFs after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (info_ptr && info_ptr->valid & PNG_INFO_oFFs)
   {
      png_warning(png_ptr, "Duplicate oFFs chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (length != 9)
   {
      png_warning(png_ptr, "Incorrect oFFs chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, 9);
   if (png_crc_finish(png_ptr, 0))
      return;

   offset_x = png_get_uint_32(buf);
   offset_y = png_get_uint_32(buf + 4);
   unit_type = buf[8];
   png_read_oFFs(png_ptr, info_ptr, offset_x, offset_y, unit_type);
}
#endif

#if defined(PNG_READ_tIME_SUPPORTED)
void
png_handle_tIME(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_byte buf[7];
   png_time mod_time;

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Out of place tIME chunk");
   else if (info_ptr && info_ptr->valid & PNG_INFO_tIME)
   {
      png_warning(png_ptr, "Duplicate tIME chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (png_ptr->mode & PNG_HAVE_IDAT)
      png_ptr->mode |= PNG_AFTER_IDAT;

   if (length != 7)
   {
      png_warning(png_ptr, "Incorrect tIME chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, 7);
   if (png_crc_finish(png_ptr, 0))
      return;

   mod_time.second = buf[6];
   mod_time.minute = buf[5];
   mod_time.hour = buf[4];
   mod_time.day = buf[3];
   mod_time.month = buf[2];
   mod_time.year = png_get_uint_16(buf);

   png_read_tIME(png_ptr, info_ptr, &mod_time);
}
#endif

#if defined(PNG_READ_tEXt_SUPPORTED)
/* note: this does not correctly handle chunks that are > 64K */
void
png_handle_tEXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_charp key;
   png_charp text;

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before tEXt");

   if (png_ptr->mode & PNG_HAVE_IDAT)
      png_ptr->mode |= PNG_AFTER_IDAT;

   key = (png_charp )png_malloc(png_ptr, length + 1);
   png_crc_read(png_ptr, (png_bytep )key, length);
   if (png_crc_finish(png_ptr, 0))
   {
      png_free(png_ptr, key);
      return;
   }

   key[(png_size_t)length] = '\0';

   for (text = key; *text; text++)
      /* empty loop to check key length */ ;

   if (text != key + (png_size_t)length)
      text++;

   png_read_tEXt(png_ptr, info_ptr, key, text, length - (text - key));
}
#endif

#if defined(PNG_READ_zTXt_SUPPORTED)
/* note: this does not correctly handle chunks that are > 64K compressed
   on those systems that can't malloc more than 64KB at a time. */
void
png_handle_zTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   static char msg[] = "Error decoding zTXt chunk";
   png_charp key;
   png_charp text;
   png_uint_32 text_size, key_size;

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before zTXt");

   if (png_ptr->mode & PNG_HAVE_IDAT)
      png_ptr->mode |= PNG_AFTER_IDAT;

   key = png_malloc(png_ptr, length + 1);
   png_crc_read(png_ptr, (png_bytep )key, length);
   if (png_crc_finish(png_ptr, 0))
   {
      png_free(png_ptr, key);
      return;
   }

   key[(png_size_t)length] = '\0';

   for (text = key; *text; text++)
      /* empty loop */ ;

   /* zTXt can't have zero text */
   if (text == key + (png_size_t)length)
   {
      png_warning(png_ptr, "Zero length zTXt chunk");
      text_size = 0;
   }
   else if (*(++text)) /* check compression type byte */
   {
      png_warning(png_ptr, "Unknown zTXt compression type");

      /* Copy what we can of the error message into the text chunk */
      text_size = length - (text - key) - 1;
      text_size = sizeof(msg) > text_size ? text_size : sizeof(msg);
      png_memcpy(text, msg, (png_size_t)(text_size + 1));
   }
   else
   {
      text++;

      png_ptr->zstream.next_in = (png_bytep )text;
      png_ptr->zstream.avail_in = (uInt)(length - (text - key));
      png_ptr->zstream.next_out = png_ptr->zbuf;
      png_ptr->zstream.avail_out = (png_size_t)png_ptr->zbuf_size;

      key_size = text - key;
      text_size = 0;
      text = NULL;

      while (png_ptr->zstream.avail_in)
      {
         int ret;

         ret = inflate(&png_ptr->zstream, Z_PARTIAL_FLUSH);
         if (ret != Z_OK && ret != Z_STREAM_END)
         {
            if (png_ptr->zstream.msg)
               png_warning(png_ptr, png_ptr->zstream.msg);
            else
               png_warning(png_ptr, "zTXt decompression error");
            inflateReset(&png_ptr->zstream);
            png_ptr->zstream.avail_in = 0;

            if (!text)
            {
               text_size = key_size + sizeof(msg) + 1;
               text = (png_charp)png_malloc(png_ptr, text_size);
               png_memcpy(text, key, (png_size_t)key_size);
            }

            text[text_size - 1] = '\0';

            /* Copy what we can of the error message into the text chunk */
            text_size = length - (text - key) - 1;
            text_size = sizeof(msg) > text_size ? text_size : sizeof(msg);
            png_memcpy(text + key_size, msg, (png_size_t)(text_size + 1));
            break;
         }
         if (!png_ptr->zstream.avail_out || ret == Z_STREAM_END)
         {
            if (!text)
            {
               text = (png_charp)png_malloc(png_ptr,
                  png_ptr->zbuf_size - png_ptr->zstream.avail_out +
                     key_size + 1);
               png_memcpy(text + (png_size_t)key_size, png_ptr->zbuf,
                  (png_size_t)(png_ptr->zbuf_size - png_ptr->zstream.avail_out));
               png_memcpy(text, key, (png_size_t)key_size);
               text_size = key_size + (png_size_t)png_ptr->zbuf_size -
                  png_ptr->zstream.avail_out;
               *(text + (png_size_t)text_size) = '\0';
            }
            else
            {
               png_charp tmp;

               tmp = text;
               text = png_malloc(png_ptr, text_size +
                  png_ptr->zbuf_size - png_ptr->zstream.avail_out + 1);
               png_memcpy(text, tmp, (png_size_t)text_size);
               png_free(png_ptr, tmp);
               png_memcpy(text + (png_size_t)text_size, png_ptr->zbuf,
                  (png_size_t)(png_ptr->zbuf_size - png_ptr->zstream.avail_out));
               text_size += png_ptr->zbuf_size - png_ptr->zstream.avail_out;
               *(text + (png_size_t)text_size) = '\0';
            }
            if (ret != Z_STREAM_END)
            {
               png_ptr->zstream.next_out = png_ptr->zbuf;
               png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
            }
            else
            {
               break;
            }
         }
      }

      inflateReset(&png_ptr->zstream);
      png_ptr->zstream.avail_in = 0;

      png_free(png_ptr, key);
      key = text;
      text += (png_size_t)key_size;
      text_size -= key_size;
   }

   png_read_zTXt(png_ptr, info_ptr, key, text, text_size, 0);
}
#endif

/* This function is called when we haven't found a handler for a
   chunk.  If there isn't a problem with the chunk itself (ie bad
   chunk name or a critical chunk), the chunk is silently ignored. */
void
png_handle_unknown(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   /* In the future we can have code here that calls user-supplied
    * callback functions for unknown chunks before they are ignored or
    * cause an error.
    */
   png_check_chunk_name(png_ptr, png_ptr->chunk_name);

   if (!(png_ptr->chunk_name[0] & 0x20))
   {
      char msg[40];

      sprintf(msg, "Unknown critical chunk %s", png_ptr->chunk_name);
      png_error(png_ptr, msg);
   }

   if (png_ptr->mode & PNG_HAVE_IDAT)
      png_ptr->mode |= PNG_AFTER_IDAT;

   png_crc_finish(png_ptr, length);
}

/* This function is called to verify that a chunk name is valid.
   This function can't have the "critical chunk check" incorporated
   into it, as in the future, we will need to be able to call user
   functions to handle unknown critical chunks after we check that
   the chunk name itself is valid. */
void
png_check_chunk_name(png_structp png_ptr, png_bytep chunk_name)
{
   if (chunk_name[0] < 41 || chunk_name[0] > 122  ||
       (chunk_name[0] > 90 && chunk_name[0] < 97) ||
       chunk_name[1] < 41 || chunk_name[1] > 122  ||
       (chunk_name[1] > 90 && chunk_name[1] < 97) ||
       chunk_name[2] < 41 || chunk_name[2] > 122  ||
       (chunk_name[2] > 90 && chunk_name[2] < 97) ||
       chunk_name[3] < 41 || chunk_name[3] > 122  ||
       (chunk_name[3] > 90 && chunk_name[3] < 97))
   {
      char msg[45];

      sprintf(msg, "Invalid chunk type 0x%02X 0x%02X 0x%02X 0x%02X",
         chunk_name[0], chunk_name[1], chunk_name[2], chunk_name[3]);
      png_error(png_ptr, msg);
   }
}

/* Combines the row recently read in with the previous row.
   This routine takes care of alpha and transparency if requested.
   This routine also handles the two methods of progressive display
   of interlaced images, depending on the mask value.
   The mask value describes which pixels are to be combined with
   the row.  The pattern always repeats every 8 pixels, so just 8
   bits are needed.  A one indicates the pixels is to be combined,
   a zero indicates the pixel is to be skipped.  This is in addition
   to any alpha or transparency value associated with the pixel.  If
   you want all pixels to be combined, pass 0xff (255) in mask.  */
void
png_combine_row(png_structp png_ptr, png_bytep row,
   int mask)
{
   if (mask == 0xff)
   {
      png_memcpy(row, png_ptr->row_buf + 1,
         (png_size_t)((png_ptr->width *
         png_ptr->row_info.pixel_depth + 7) >> 3));
   }
   else
   {
      switch (png_ptr->row_info.pixel_depth)
      {
         case 1:
         {
            png_bytep sp;
            png_bytep dp;
            int m;
            int shift;
            png_uint_32 i;
            int value;

            sp = png_ptr->row_buf + 1;
            dp = row;
            shift = 7;
            m = 0x80;
            for (i = 0; i < png_ptr->width; i++)
            {
               if (m & mask)
               {
                  value = (*sp >> shift) & 0x1;
                  *dp &= (png_byte)((0x7f7f >> (7 - shift)) & 0xff);
                  *dp |= (png_byte)(value << shift);
               }

               if (shift == 0)
               {
                  shift = 7;
                  sp++;
                  dp++;
               }
               else
                  shift--;

               if (m == 1)
                  m = 0x80;
               else
                  m >>= 1;
            }
            break;
         }
         case 2:
         {
            png_bytep sp;
            png_bytep dp;
            int m;
            int shift;
            png_uint_32 i;
            int value;

            sp = png_ptr->row_buf + 1;
            dp = row;
            shift = 6;
            m = 0x80;
            for (i = 0; i < png_ptr->width; i++)
            {
               if (m & mask)
               {
                  value = (*sp >> shift) & 0x3;
                  *dp &= (png_byte)((0x3f3f >> (6 - shift)) & 0xff);
                  *dp |= (png_byte)(value << shift);
               }

               if (shift == 0)
               {
                  shift = 6;
                  sp++;
                  dp++;
               }
               else
                  shift -= 2;
               if (m == 1)
                  m = 0x80;
               else
                  m >>= 1;
            }
            break;
         }
         case 4:
         {
            png_bytep sp;
            png_bytep dp;
            int m;
            int shift;
            png_uint_32 i;
            int value;

            sp = png_ptr->row_buf + 1;
            dp = row;
            shift = 4;
            m = 0x80;
            for (i = 0; i < png_ptr->width; i++)
            {
               if (m & mask)
               {
                  value = (*sp >> shift) & 0xf;
                  *dp &= (png_byte)((0xf0f >> (4 - shift)) & 0xff);
                  *dp |= (png_byte)(value << shift);
               }

               if (shift == 0)
               {
                  shift = 4;
                  sp++;
                  dp++;
               }
               else
                  shift -= 4;
               if (m == 1)
                  m = 0x80;
               else
                  m >>= 1;
            }
            break;
         }
         default:
         {
            png_bytep sp;
            png_bytep dp;
            png_uint_32 i, pixel_bytes;
            png_byte m;

            pixel_bytes = (png_ptr->row_info.pixel_depth >> 3);

            sp = png_ptr->row_buf + 1;
            dp = row;
            m = 0x80;
            for (i = 0; i < png_ptr->width; i++)
            {
               if (m & mask)
               {
                  png_memcpy(dp, sp, pixel_bytes);
               }

               sp += pixel_bytes;
               dp += pixel_bytes;

               if (m == 1)
                  m = 0x80;
               else
                  m >>= 1;
            }
            break;
         }
      }
   }
}

#if defined(PNG_READ_INTERLACING_SUPPORTED)
void
png_do_read_interlace(png_row_infop row_info, png_bytep row, int pass)
{
   if (row && row_info)
   {
      png_uint_32 final_width;

      final_width = row_info->width * png_pass_inc[pass];

      switch (row_info->pixel_depth)
      {
         case 1:
         {
            png_bytep sp, dp;
            int sshift, dshift;
            png_byte v;
            png_uint_32 i;
            int j;

            sp = row + (png_size_t)((row_info->width - 1) >> 3);
            sshift = 7 - (int)((row_info->width + 7) & 7);
            dp = row + (png_size_t)((final_width - 1) >> 3);
            dshift = 7 - (int)((final_width + 7) & 7);
            for (i = row_info->width; i; i--)
            {
               v = (png_byte)((*sp >> sshift) & 0x1);
               for (j = 0; j < png_pass_inc[pass]; j++)
               {
                  *dp &= (png_byte)((0x7f7f >> (7 - dshift)) & 0xff);
                  *dp |= (png_byte)(v << dshift);
                  if (dshift == 7)
                  {
                     dshift = 0;
                     dp--;
                  }
                  else
                     dshift++;
               }
               if (sshift == 7)
               {
                  sshift = 0;
                  sp--;
               }
               else
                  sshift++;
            }
            break;
         }
         case 2:
         {
            png_bytep sp, dp;
            int sshift, dshift;
            png_byte v;
            png_uint_32 i, j;

            sp = row + (png_size_t)((row_info->width - 1) >> 2);
            sshift = (png_size_t)((3 - ((row_info->width + 3) & 3)) << 1);
            dp = row + (png_size_t)((final_width - 1) >> 2);
            dshift = (png_size_t)((3 - ((final_width + 3) & 3)) << 1);
            for (i = row_info->width; i; i--)
            {
               v = (png_byte)((*sp >> sshift) & 0x3);
               for (j = 0; j < png_pass_inc[pass]; j++)
               {
                  *dp &= (png_byte)((0x3f3f >> (6 - dshift)) & 0xff);
                  *dp |= (png_byte)(v << dshift);
                  if (dshift == 6)
                  {
                     dshift = 0;
                     dp--;
                  }
                  else
                     dshift += 2;
               }
               if (sshift == 6)
               {
                  sshift = 0;
                  sp--;
               }
               else
                  sshift += 2;
            }
            break;
         }
         case 4:
         {
            png_bytep sp, dp;
            int sshift, dshift;
            png_byte v;
            png_uint_32 i;
            int j;

            sp = row + (png_size_t)((row_info->width - 1) >> 1);
            sshift = (png_size_t)((1 - ((row_info->width + 1) & 1)) << 2);
            dp = row + (png_size_t)((final_width - 1) >> 1);
            dshift = (png_size_t)((1 - ((final_width + 1) & 1)) << 2);
            for (i = row_info->width; i; i--)
            {
               v = (png_byte)((*sp >> sshift) & 0xf);
               for (j = 0; j < png_pass_inc[pass]; j++)
               {
                  *dp &= (png_byte)((0xf0f >> (4 - dshift)) & 0xff);
                  *dp |= (png_byte)(v << dshift);
                  if (dshift == 4)
                  {
                     dshift = 0;
                     dp--;
                  }
                  else
                     dshift = 4;
               }
               if (sshift == 4)
               {
                  sshift = 0;
                  sp--;
               }
               else
                  sshift = 4;
            }
            break;
         }
         default:
         {
            png_bytep sp, dp;
            png_byte v[8];
            png_uint_32 i, pixel_bytes;
            int j;

            pixel_bytes = (row_info->pixel_depth >> 3);

            sp = row + (png_size_t)((row_info->width - 1) * pixel_bytes);
            dp = row + (png_size_t)((final_width - 1) * pixel_bytes);
            for (i = row_info->width; i; i--)
            {
               png_memcpy(v, sp, pixel_bytes);
               for (j = 0; j < png_pass_inc[pass]; j++)
               {
                  png_memcpy(dp, v, pixel_bytes);
                  dp -= pixel_bytes;
               }
               sp -= pixel_bytes;
            }
            break;
         }
      }
      row_info->width = final_width;
      row_info->rowbytes = ((final_width *
         (png_uint_32)row_info->pixel_depth + 7) >> 3);
   }
}
#endif

void
png_read_filter_row(png_structp png_ptr, png_row_infop row_info, png_bytep row,
   png_bytep prev_row, int filter)
{
   switch (filter)
   {
      case 0:
         break;
      case 1:
      {
         png_uint_32 i;
         int bpp;
         png_bytep rp;
         png_bytep lp;

         bpp = (row_info->pixel_depth + 7) / 8;
         for (i = (png_uint_32)bpp, rp = row + bpp, lp = row;
            i < row_info->rowbytes; i++, rp++, lp++)
         {
            *rp = (png_byte)(((int)(*rp) + (int)(*lp)) & 0xff);
         }
         break;
      }
      case 2:
      {
         png_uint_32 i;
         png_bytep rp;
         png_bytep pp;

         for (i = 0, rp = row, pp = prev_row;
            i < row_info->rowbytes; i++, rp++, pp++)
         {
            *rp = (png_byte)(((int)(*rp) + (int)(*pp)) & 0xff);
         }
         break;
      }
      case 3:
      {
         png_uint_32 i;
         int bpp;
         png_bytep rp;
         png_bytep pp;
         png_bytep lp;

         bpp = (row_info->pixel_depth + 7) / 8;
         for (i = 0, rp = row, pp = prev_row;
            i < (png_uint_32)bpp; i++, rp++, pp++)
         {
            *rp = (png_byte)(((int)(*rp) +
               ((int)(*pp) / 2)) & 0xff);
         }
         for (lp = row; i < row_info->rowbytes; i++, rp++, lp++, pp++)
         {
            *rp = (png_byte)(((int)(*rp) +
               (int)(*pp + *lp) / 2) & 0xff);
         }
         break;
      }
      case 4:
      {
         int bpp;
         png_uint_32 i;
         png_bytep rp;
         png_bytep pp;
         png_bytep lp;
         png_bytep cp;

         bpp = (row_info->pixel_depth + 7) / 8;
         for (i = 0, rp = row, pp = prev_row,
            lp = row - bpp, cp = prev_row - bpp;
            i < row_info->rowbytes; i++, rp++, pp++, lp++, cp++)
         {
            int a, b, c, pa, pb, pc, p;

            b = *pp;
            if (i >= (png_uint_32)bpp)
            {
               c = *cp;
               a = *lp;
            }
            else
            {
               a = c = 0;
            }
            p = a + b - c;
            pa = abs(p - a);
            pb = abs(p - b);
            pc = abs(p - c);

            if (pa <= pb && pa <= pc)
               p = a;
            else if (pb <= pc)
               p = b;
            else
               p = c;

            *rp = (png_byte)(((int)(*rp) + p) & 0xff);
         }
         break;
      }
      default:
         png_error(png_ptr, "Bad adaptive filter type");
         break;
   }
}

void
png_read_finish_row(png_structp png_ptr)
{
   png_ptr->row_number++;
   if (png_ptr->row_number < png_ptr->num_rows)
      return;

   if (png_ptr->interlaced)
   {
      png_ptr->row_number = 0;
      png_memset(png_ptr->prev_row, 0, (png_size_t)png_ptr->rowbytes + 1);
      do
      {
         png_ptr->pass++;
         if (png_ptr->pass >= 7)
            break;
         png_ptr->iwidth = (png_ptr->width +
            png_pass_inc[png_ptr->pass] - 1 -
            png_pass_start[png_ptr->pass]) /
            png_pass_inc[png_ptr->pass];
         png_ptr->irowbytes = ((png_ptr->iwidth *
            png_ptr->pixel_depth + 7) >> 3) + 1;
         if (!(png_ptr->transformations & PNG_INTERLACE))
         {
            png_ptr->num_rows = (png_ptr->height +
               png_pass_yinc[png_ptr->pass] - 1 -
               png_pass_ystart[png_ptr->pass]) /
               png_pass_yinc[png_ptr->pass];
            if (!(png_ptr->num_rows))
               continue;
         }
         if (png_ptr->transformations & PNG_INTERLACE)
            break;
      } while (png_ptr->iwidth == 0);

      if (png_ptr->pass < 7)
         return;
   }

   if (!(png_ptr->flags & PNG_FLAG_ZLIB_FINISHED))
   {
      char extra;
      int ret;

      png_ptr->zstream.next_out = (Byte *)&extra;
      png_ptr->zstream.avail_out = (uInt)1;
      do
      {
         if (!(png_ptr->zstream.avail_in))
         {
            while (!png_ptr->idat_size)
            {
               png_byte chunk_length[4];

               png_crc_finish(png_ptr, 0);

               png_read_data(png_ptr, chunk_length, 4);
               png_ptr->idat_size = png_get_uint_32(chunk_length);

               png_reset_crc(png_ptr);
               png_crc_read(png_ptr, png_ptr->chunk_name, 4);
               if (png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
                  png_error(png_ptr, "Not enough image data");

            }
            png_ptr->zstream.avail_in = (uInt)png_ptr->zbuf_size;
            png_ptr->zstream.next_in = png_ptr->zbuf;
            if (png_ptr->zbuf_size > png_ptr->idat_size)
               png_ptr->zstream.avail_in = (uInt)png_ptr->idat_size;
            png_crc_read(png_ptr, png_ptr->zbuf, png_ptr->zstream.avail_in);
            png_ptr->idat_size -= png_ptr->zstream.avail_in;
         }
         ret = inflate(&png_ptr->zstream, Z_PARTIAL_FLUSH);
         if (ret == Z_STREAM_END)
         {
            if (!(png_ptr->zstream.avail_out) || png_ptr->zstream.avail_in ||
               png_ptr->idat_size)
               png_error(png_ptr, "Extra compressed data");
            png_ptr->mode |= PNG_AFTER_IDAT;
            png_ptr->flags |= PNG_FLAG_ZLIB_FINISHED;
            break;
         }
         if (ret != Z_OK)
            png_error(png_ptr, png_ptr->zstream.msg ? png_ptr->zstream.msg :
                      "Decompression Error");

         if (!(png_ptr->zstream.avail_out))
            png_error(png_ptr, "Extra compressed data");

      } while (1);
      png_ptr->zstream.avail_out = 0;
   }

   if (png_ptr->idat_size || png_ptr->zstream.avail_in)
      png_error(png_ptr, "Extra compression data");

   inflateReset(&png_ptr->zstream);

   png_ptr->mode |= PNG_AFTER_IDAT;
}

void
png_read_start_row(png_structp png_ptr)
{
   int max_pixel_depth;
   png_uint_32 rowbytes;

   png_ptr->zstream.avail_in = 0;
   png_init_read_transformations(png_ptr);
   if (png_ptr->interlaced)
   {
      if (!(png_ptr->transformations & PNG_INTERLACE))
         png_ptr->num_rows = (png_ptr->height + png_pass_yinc[0] - 1 -
            png_pass_ystart[0]) / png_pass_yinc[0];
      else
         png_ptr->num_rows = png_ptr->height;

      png_ptr->iwidth = (png_ptr->width +
         png_pass_inc[png_ptr->pass] - 1 -
         png_pass_start[png_ptr->pass]) /
         png_pass_inc[png_ptr->pass];
      png_ptr->irowbytes = ((png_ptr->iwidth *
         png_ptr->pixel_depth + 7) >> 3) + 1;
   }
   else
   {
      png_ptr->num_rows = png_ptr->height;
      png_ptr->iwidth = png_ptr->width;
      png_ptr->irowbytes = png_ptr->rowbytes + 1;
   }

   max_pixel_depth = png_ptr->pixel_depth;

#if defined(PNG_READ_PACK_SUPPORTED)
   if ((png_ptr->transformations & PNG_PACK) && png_ptr->bit_depth < 8)
      max_pixel_depth = 8;
#endif

#if defined(PNG_READ_EXPAND_SUPPORTED)
   if (png_ptr->transformations & PNG_EXPAND)
   {
      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      {
         if (png_ptr->num_trans)
            max_pixel_depth = 32;
         else
            max_pixel_depth = 24;
      }
      else if (png_ptr->color_type == PNG_COLOR_TYPE_GRAY)
      {
         if (max_pixel_depth < 8)
            max_pixel_depth = 8;
         if (png_ptr->num_trans)
            max_pixel_depth *= 2;
      }
      else if (png_ptr->color_type == PNG_COLOR_TYPE_RGB)
      {
         if (png_ptr->num_trans)
         {
            max_pixel_depth *= 4;
            max_pixel_depth /= 3;
         }
      }
   }
#endif

#if defined(PNG_READ_FILLER_SUPPORTED)
   if (png_ptr->transformations & (PNG_FILLER))
   {
      if (max_pixel_depth < 32)
         max_pixel_depth = 32;
   }
#endif

#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
   if (png_ptr->transformations & PNG_GRAY_TO_RGB)
   {
      if ((png_ptr->num_trans && (png_ptr->transformations & PNG_EXPAND)) ||
         png_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
      {
         if (max_pixel_depth <= 16)
            max_pixel_depth = 32;
         else if (max_pixel_depth <= 32)
            max_pixel_depth = 64;
      }
      else
      {
         if (max_pixel_depth <= 8)
            max_pixel_depth = 24;
         else if (max_pixel_depth <= 16)
            max_pixel_depth = 48;
      }
   }
#endif

   /* align the width on the next larger 8 pixels.  Mainly used
      for interlacing */
   rowbytes = ((png_ptr->width + 7) & ~((png_uint_32)7));
   /* calculate the maximum bytes needed, adding a byte and a pixel
      for safety sake */
   rowbytes = ((rowbytes * (png_uint_32)max_pixel_depth + 7) >> 3) +
      1 + ((max_pixel_depth + 7) >> 3);
#ifdef PNG_MAX_MALLOC_64K
   if (rowbytes > 65536L)
      png_error(png_ptr, "This image requires a row greater than 64KB");
#endif
   png_ptr->row_buf = (png_bytep )png_malloc(png_ptr, rowbytes);

#ifdef PNG_MAX_MALLOC_64K
   if (png_ptr->rowbytes + 1 > 65536L)
      png_error(png_ptr, "This image requires a row greater than 64KB");
#endif
   png_ptr->prev_row = png_malloc(png_ptr, png_ptr->rowbytes + 1);

   png_memset(png_ptr->prev_row, 0, (png_size_t)png_ptr->rowbytes + 1);

   png_ptr->flags |= PNG_FLAG_ROW_INIT;
}
