
/* pngrutil.c - utilities to read a PNG file
 *
 * Last changed in libpng 1.2.34 [December 11, 2008]
 * For conditions of distribution and use, see copyright notice in png.h
 * Copyright (c) 1998-2008 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 *
 * This file contains routines that are only called from within
 * libpng itself during the course of reading an image.
 */

#define PNG_INTERNAL
#include "png.h"
#if defined(PNG_READ_SUPPORTED)

#if defined(_WIN32_WCE) && (_WIN32_WCE<0x500)
#  define WIN32_WCE_OLD
#endif

#ifdef PNG_FLOATING_POINT_SUPPORTED
#  if defined(WIN32_WCE_OLD)
/* strtod() function is not supported on WindowsCE */
__inline double png_strtod(png_structp png_ptr, PNG_CONST char *nptr, char **endptr)
{
   double result = 0;
   int len;
   wchar_t *str, *end;

   len = MultiByteToWideChar(CP_ACP, 0, nptr, -1, NULL, 0);
   str = (wchar_t *)png_malloc(png_ptr, len * png_sizeof(wchar_t));
   if ( NULL != str )
   {
      MultiByteToWideChar(CP_ACP, 0, nptr, -1, str, len);
      result = wcstod(str, &end);
      len = WideCharToMultiByte(CP_ACP, 0, end, -1, NULL, 0, NULL, NULL);
      *endptr = (char *)nptr + (png_strlen(nptr) - len + 1);
      png_free(png_ptr, str);
   }
   return result;
}
#  else
#    define png_strtod(p,a,b) strtod(a,b)
#  endif
#endif

png_uint_32 PNGAPI
png_get_uint_31(png_structp png_ptr, png_bytep buf)
{
#ifdef PNG_READ_BIG_ENDIAN_SUPPORTED
   png_uint_32 i = png_get_uint_32(buf);
#else
   /* Avoid an extra function call by inlining the result. */
   png_uint_32 i = ((png_uint_32)(*buf) << 24) +
      ((png_uint_32)(*(buf + 1)) << 16) +
      ((png_uint_32)(*(buf + 2)) << 8) +
      (png_uint_32)(*(buf + 3));
#endif
   if (i > PNG_UINT_31_MAX)
     png_error(png_ptr, "PNG unsigned integer out of range.");
   return (i);
}
#ifndef PNG_READ_BIG_ENDIAN_SUPPORTED
/* Grab an unsigned 32-bit integer from a buffer in big-endian format. */
png_uint_32 PNGAPI
png_get_uint_32(png_bytep buf)
{
   png_uint_32 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 a signed 32-bit integer from a buffer in big-endian format.  The
 * data is stored in the PNG file in two's complement format, and it is
 * assumed that the machine format for signed integers is the same. */
png_int_32 PNGAPI
png_get_int_32(png_bytep buf)
{
   png_int_32 i = ((png_int_32)(*buf) << 24) +
      ((png_int_32)(*(buf + 1)) << 16) +
      ((png_int_32)(*(buf + 2)) << 8) +
      (png_int_32)(*(buf + 3));

   return (i);
}

/* Grab an unsigned 16-bit integer from a buffer in big-endian format. */
png_uint_16 PNGAPI
png_get_uint_16(png_bytep buf)
{
   png_uint_16 i = (png_uint_16)(((png_uint_16)(*buf) << 8) +
      (png_uint_16)(*(buf + 1)));

   return (i);
}
#endif /* PNG_READ_BIG_ENDIAN_SUPPORTED */

/* Read the chunk header (length + type name).
 * Put the type name into png_ptr->chunk_name, and return the length.
 */
png_uint_32 /* PRIVATE */
png_read_chunk_header(png_structp png_ptr)
{
   png_byte buf[8];
   png_uint_32 length;

   /* read the length and the chunk name */
   png_read_data(png_ptr, buf, 8);
   length = png_get_uint_31(png_ptr, buf);

   /* put the chunk name into png_ptr->chunk_name */
   png_memcpy(png_ptr->chunk_name, buf + 4, 4);

   png_debug2(0, "Reading %s chunk, length = %lu",
      png_ptr->chunk_name, length);

   /* reset the crc and run it over the chunk name */
   png_reset_crc(png_ptr);
   png_calculate_crc(png_ptr, png_ptr->chunk_name, 4);

   /* check to see if chunk name is valid */
   png_check_chunk_name(png_ptr, png_ptr->chunk_name);

   return length;
}

/* Read data, and (optionally) run it through the CRC. */
void /* PRIVATE */
png_crc_read(png_structp png_ptr, png_bytep buf, png_size_t length)
{
   if (png_ptr == NULL) return;
   png_read_data(png_ptr, buf, length);
   png_calculate_crc(png_ptr, buf, length);
}

/* Optionally skip data and then check the CRC.  Depending on whether we
   are reading 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.
   Returns '1' if there was a CRC error, '0' otherwise. */
int /* PRIVATE */
png_crc_finish(png_structp png_ptr, png_uint_32 skip)
{
   png_size_t i;
   png_size_t istop = png_ptr->zbuf_size;

   for (i = (png_size_t)skip; i > istop; i -= istop)
   {
      png_crc_read(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
   }
   if (i)
   {
      png_crc_read(png_ptr, png_ptr->zbuf, i);
   }

   if (png_crc_error(png_ptr))
   {
      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_chunk_warning(png_ptr, "CRC error");
      }
      else
      {
         png_chunk_error(png_ptr, "CRC error");
      }
      return (1);
   }

   return (0);
}

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

   if (need_crc)
   {
      crc = png_get_uint_32(crc_bytes);
      return ((int)(crc != png_ptr->crc));
   }
   else
      return (0);
}

#if defined(PNG_READ_zTXt_SUPPORTED) || defined(PNG_READ_iTXt_SUPPORTED) || \
    defined(PNG_READ_iCCP_SUPPORTED)
/*
 * Decompress trailing data in a chunk.  The assumption is that chunkdata
 * points at an allocated area holding the contents of a chunk with a
 * trailing compressed part.  What we get back is an allocated area
 * holding the original prefix part and an uncompressed version of the
 * trailing part (the malloc area passed in is freed).
 */
void /* PRIVATE */
png_decompress_chunk(png_structp png_ptr, int comp_type,
                              png_size_t chunklength,
                              png_size_t prefix_size, png_size_t *newlength)
{
   static PNG_CONST char msg[] = "Error decoding compressed text";
   png_charp text;
   png_size_t text_size;

   if (comp_type == PNG_COMPRESSION_TYPE_BASE)
   {
      int ret = Z_OK;
      png_ptr->zstream.next_in = (png_bytep)(png_ptr->chunkdata + prefix_size);
      png_ptr->zstream.avail_in = (uInt)(chunklength - prefix_size);
      png_ptr->zstream.next_out = png_ptr->zbuf;
      png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;

      text_size = 0;
      text = NULL;

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

            if (text ==  NULL)
            {
               text_size = prefix_size + png_sizeof(msg) + 1;
               text = (png_charp)png_malloc_warn(png_ptr, text_size);
               if (text ==  NULL)
                 {
                    png_free(png_ptr, png_ptr->chunkdata);
                    png_ptr->chunkdata = NULL;
                    png_error(png_ptr, "Not enough memory to decompress chunk");
                 }
               png_memcpy(text, png_ptr->chunkdata, prefix_size);
            }

            text[text_size - 1] = 0x00;

            /* Copy what we can of the error message into the text chunk */
            text_size = (png_size_t)(chunklength -
              (text - png_ptr->chunkdata) - 1);
            if (text_size > png_sizeof(msg))
               text_size = png_sizeof(msg);
            png_memcpy(text + prefix_size, msg, text_size);
            break;
         }
         if (!png_ptr->zstream.avail_out || ret == Z_STREAM_END)
         {
            if (text == NULL)
            {
               text_size = prefix_size +
                   png_ptr->zbuf_size - png_ptr->zstream.avail_out;
               text = (png_charp)png_malloc_warn(png_ptr, text_size + 1);
               if (text ==  NULL)
               {
                  png_free(png_ptr, png_ptr->chunkdata);
                  png_ptr->chunkdata = NULL;
                  png_error(png_ptr,
                    "Not enough memory to decompress chunk.");
               }
               png_memcpy(text + prefix_size, png_ptr->zbuf,
                    text_size - prefix_size);
               png_memcpy(text, png_ptr->chunkdata, prefix_size);
               *(text + text_size) = 0x00;
            }
            else
            {
               png_charp tmp;

               tmp = text;
               text = (png_charp)png_malloc_warn(png_ptr,
                  (png_uint_32)(text_size +
                  png_ptr->zbuf_size - png_ptr->zstream.avail_out + 1));
               if (text == NULL)
               {
                  png_free(png_ptr, tmp);
                  png_free(png_ptr, png_ptr->chunkdata);
                  png_ptr->chunkdata = NULL;
                  png_error(png_ptr,
                    "Not enough memory to decompress chunk..");
               }
               png_memcpy(text, tmp, text_size);
               png_free(png_ptr, tmp);
               png_memcpy(text + text_size, png_ptr->zbuf,
                  (png_ptr->zbuf_size - png_ptr->zstream.avail_out));
               text_size += png_ptr->zbuf_size - png_ptr->zstream.avail_out;
               *(text + text_size) = 0x00;
            }
            if (ret == Z_STREAM_END)
               break;
            else
            {
               png_ptr->zstream.next_out = png_ptr->zbuf;
               png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
            }
         }
      }
      if (ret != Z_STREAM_END)
      {
#if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
         char umsg[52];

         if (ret == Z_BUF_ERROR)
            png_snprintf(umsg, 52,
                "Buffer error in compressed datastream in %s chunk",
                png_ptr->chunk_name);
         else if (ret == Z_DATA_ERROR)
            png_snprintf(umsg, 52,
                "Data error in compressed datastream in %s chunk",
                png_ptr->chunk_name);
         else
            png_snprintf(umsg, 52,
                "Incomplete compressed datastream in %s chunk",
                png_ptr->chunk_name);
         png_warning(png_ptr, umsg);
#else
         png_warning(png_ptr,
            "Incomplete compressed datastream in chunk other than IDAT");
#endif
         text_size = prefix_size;
         if (text ==  NULL)
         {
            text = (png_charp)png_malloc_warn(png_ptr, text_size+1);
            if (text == NULL)
              {
                png_free(png_ptr, png_ptr->chunkdata);
                png_ptr->chunkdata = NULL;
                png_error(png_ptr, "Not enough memory for text.");
              }
            png_memcpy(text, png_ptr->chunkdata, prefix_size);
         }
         *(text + text_size) = 0x00;
      }

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

      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = text;
      *newlength=text_size;
   }
   else /* if (comp_type != PNG_COMPRESSION_TYPE_BASE) */
   {
#if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
      char umsg[50];

      png_snprintf(umsg, 50, "Unknown zTXt compression type %d", comp_type);
      png_warning(png_ptr, umsg);
#else
      png_warning(png_ptr, "Unknown zTXt compression type");
#endif

      *(png_ptr->chunkdata + prefix_size) = 0x00;
      *newlength = prefix_size;
   }
}
#endif

/* read and check the IDHR chunk */
void /* PRIVATE */
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;

   png_debug(1, "in png_handle_IHDR");

   if (png_ptr->mode & PNG_HAVE_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_31(png_ptr, buf);
   height = png_get_uint_31(png_ptr, buf + 4);
   bit_depth = buf[8];
   color_type = buf[9];
   compression_type = buf[10];
   filter_type = buf[11];
   interlace_type = buf[12];

   /* 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;
#if defined(PNG_MNG_FEATURES_SUPPORTED)
   png_ptr->filter_type = (png_byte)filter_type;
#endif
   png_ptr->compression_type = (png_byte)compression_type;

   /* find number of channels */
   switch (png_ptr->color_type)
   {
      case PNG_COLOR_TYPE_GRAY:
      case PNG_COLOR_TYPE_PALETTE:
         png_ptr->channels = 1;
         break;
      case PNG_COLOR_TYPE_RGB:
         png_ptr->channels = 3;
         break;
      case PNG_COLOR_TYPE_GRAY_ALPHA:
         png_ptr->channels = 2;
         break;
      case PNG_COLOR_TYPE_RGB_ALPHA:
         png_ptr->channels = 4;
         break;
   }

   /* set up other useful info */
   png_ptr->pixel_depth = (png_byte)(png_ptr->bit_depth *
   png_ptr->channels);
   png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth, png_ptr->width);
   png_debug1(3, "bit_depth = %d", png_ptr->bit_depth);
   png_debug1(3, "channels = %d", png_ptr->channels);
   png_debug1(3, "rowbytes = %lu", png_ptr->rowbytes);
   png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth,
      color_type, interlace_type, compression_type, filter_type);
}

/* read and check the palette */
void /* PRIVATE */
png_handle_PLTE(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_color palette[PNG_MAX_PALETTE_LENGTH];
   int num, i;
#ifndef PNG_NO_POINTER_INDEXING
   png_colorp pal_ptr;
#endif

   png_debug(1, "in png_handle_PLTE");

   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 (!(png_ptr->color_type&PNG_COLOR_MASK_COLOR))
   {
      png_warning(png_ptr,
        "Ignoring PLTE chunk in grayscale PNG");
      png_crc_finish(png_ptr, length);
      return;
   }
#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*PNG_MAX_PALETTE_LENGTH || 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;

#ifndef PNG_NO_POINTER_INDEXING
   for (i = 0, pal_ptr = palette; i < num; i++, pal_ptr++)
   {
      png_byte buf[3];

      png_crc_read(png_ptr, buf, 3);
      pal_ptr->red = buf[0];
      pal_ptr->green = buf[1];
      pal_ptr->blue = buf[2];
   }
#else
   for (i = 0; i < num; i++)
   {
      png_byte buf[3];

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

   /* If we actually NEED the PLTE chunk (ie for a paletted image), we do
      whatever the normal CRC configuration tells us.  However, if we
      have an RGB image, the PLTE can be considered ancillary, so
      we will act as though it is. */
#if !defined(PNG_READ_OPT_PLTE_SUPPORTED)
   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
#endif
   {
      png_crc_finish(png_ptr, 0);
   }
#if !defined(PNG_READ_OPT_PLTE_SUPPORTED)
   else if (png_crc_error(png_ptr))  /* Only if we have a CRC error */
   {
      /* If we don't want to use the data from an ancillary chunk,
         we have two options: an error abort, or a warning and we
         ignore the data in this chunk (which should be OK, since
         it's considered ancillary for a RGB or RGBA image). */
      if (!(png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_USE))
      {
         if (png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN)
         {
            png_chunk_error(png_ptr, "CRC error");
         }
         else
         {
            png_chunk_warning(png_ptr, "CRC error");
            return;
         }
      }
      /* Otherwise, we (optionally) emit a warning and use the chunk. */
      else if (!(png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN))
      {
         png_chunk_warning(png_ptr, "CRC error");
      }
   }
#endif

   png_set_PLTE(png_ptr, info_ptr, palette, num);

#if defined(PNG_READ_tRNS_SUPPORTED)
   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
   {
      if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_tRNS))
      {
         if (png_ptr->num_trans > (png_uint_16)num)
         {
            png_warning(png_ptr, "Truncating incorrect tRNS chunk length");
            png_ptr->num_trans = (png_uint_16)num;
         }
         if (info_ptr->num_trans > (png_uint_16)num)
         {
            png_warning(png_ptr, "Truncating incorrect info tRNS chunk length");
            info_ptr->num_trans = (png_uint_16)num;
         }
      }
   }
#endif

}

void /* PRIVATE */
png_handle_IEND(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_debug(1, "in png_handle_IEND");

   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);

   info_ptr = info_ptr; /* quiet compiler warnings about unused info_ptr */
}

#if defined(PNG_READ_gAMA_SUPPORTED)
void /* PRIVATE */
png_handle_gAMA(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_fixed_point igamma;
#ifdef PNG_FLOATING_POINT_SUPPORTED
   float file_gamma;
#endif
   png_byte buf[4];

   png_debug(1, "in png_handle_gAMA");

   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");

   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_gAMA)
#if defined(PNG_READ_sRGB_SUPPORTED)
      && !(info_ptr->valid & PNG_INFO_sRGB)
#endif
      )
   {
      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_fixed_point)png_get_uint_32(buf);
   /* check for zero gamma */
   if (igamma == 0)
      {
         png_warning(png_ptr,
           "Ignoring gAMA chunk with gamma=0");
         return;
      }

#if defined(PNG_READ_sRGB_SUPPORTED)
   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_sRGB))
      if (PNG_OUT_OF_RANGE(igamma, 45500L, 500))
      {
         png_warning(png_ptr,
           "Ignoring incorrect gAMA value when sRGB is also present");
#ifndef PNG_NO_CONSOLE_IO
         fprintf(stderr, "gamma = (%d/100000)", (int)igamma);
#endif
         return;
      }
#endif /* PNG_READ_sRGB_SUPPORTED */

#ifdef PNG_FLOATING_POINT_SUPPORTED
   file_gamma = (float)igamma / (float)100000.0;
#  ifdef PNG_READ_GAMMA_SUPPORTED
     png_ptr->gamma = file_gamma;
#  endif
     png_set_gAMA(png_ptr, info_ptr, file_gamma);
#endif
#ifdef PNG_FIXED_POINT_SUPPORTED
   png_set_gAMA_fixed(png_ptr, info_ptr, igamma);
#endif
}
#endif

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

   png_debug(1, "in png_handle_sBIT");

   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");
   }
   if (info_ptr != NULL && (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_size_t)png_ptr->channels;

   if (length != truelen || length > 4)
   {
      png_warning(png_ptr, "Incorrect sBIT chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, truelen);
   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.red = buf[0];
      png_ptr->sig_bit.green = buf[0];
      png_ptr->sig_bit.blue = buf[0];
      png_ptr->sig_bit.alpha = buf[1];
   }
   png_set_sBIT(png_ptr, info_ptr, &(png_ptr->sig_bit));
}
#endif

#if defined(PNG_READ_cHRM_SUPPORTED)
void /* PRIVATE */
png_handle_cHRM(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_byte buf[32];
#ifdef PNG_FLOATING_POINT_SUPPORTED
   float white_x, white_y, red_x, red_y, green_x, green_y, blue_x, blue_y;
#endif
   png_fixed_point int_x_white, int_y_white, int_x_red, int_y_red, int_x_green,
      int_y_green, int_x_blue, int_y_blue;

   png_uint_32 uint_x, uint_y;

   png_debug(1, "in png_handle_cHRM");

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

   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_cHRM)
#if defined(PNG_READ_sRGB_SUPPORTED)
      && !(info_ptr->valid & PNG_INFO_sRGB)
#endif
      )
   {
      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, 32);
   if (png_crc_finish(png_ptr, 0))
      return;

   uint_x = png_get_uint_32(buf);
   uint_y = png_get_uint_32(buf + 4);
   int_x_white = (png_fixed_point)uint_x;
   int_y_white = (png_fixed_point)uint_y;

   uint_x = png_get_uint_32(buf + 8);
   uint_y = png_get_uint_32(buf + 12);
   int_x_red = (png_fixed_point)uint_x;
   int_y_red = (png_fixed_point)uint_y;

   uint_x = png_get_uint_32(buf + 16);
   uint_y = png_get_uint_32(buf + 20);
   int_x_green = (png_fixed_point)uint_x;
   int_y_green = (png_fixed_point)uint_y;

   uint_x = png_get_uint_32(buf + 24);
   uint_y = png_get_uint_32(buf + 28);
   int_x_blue = (png_fixed_point)uint_x;
   int_y_blue = (png_fixed_point)uint_y;

#ifdef PNG_FLOATING_POINT_SUPPORTED
   white_x = (float)int_x_white / (float)100000.0;
   white_y = (float)int_y_white / (float)100000.0;
   red_x   = (float)int_x_red   / (float)100000.0;
   red_y   = (float)int_y_red   / (float)100000.0;
   green_x = (float)int_x_green / (float)100000.0;
   green_y = (float)int_y_green / (float)100000.0;
   blue_x  = (float)int_x_blue  / (float)100000.0;
   blue_y  = (float)int_y_blue  / (float)100000.0;
#endif

#if defined(PNG_READ_sRGB_SUPPORTED)
   if ((info_ptr != NULL) && (info_ptr->valid & PNG_INFO_sRGB))
      {
      if (PNG_OUT_OF_RANGE(int_x_white, 31270,  1000) ||
          PNG_OUT_OF_RANGE(int_y_white, 32900,  1000) ||
          PNG_OUT_OF_RANGE(int_x_red,   64000L, 1000) ||
          PNG_OUT_OF_RANGE(int_y_red,   33000,  1000) ||
          PNG_OUT_OF_RANGE(int_x_green, 30000,  1000) ||
          PNG_OUT_OF_RANGE(int_y_green, 60000L, 1000) ||
          PNG_OUT_OF_RANGE(int_x_blue,  15000,  1000) ||
          PNG_OUT_OF_RANGE(int_y_blue,   6000,  1000))
         {
            png_warning(png_ptr,
              "Ignoring incorrect cHRM value when sRGB is also present");
#ifndef PNG_NO_CONSOLE_IO
#ifdef PNG_FLOATING_POINT_SUPPORTED
            fprintf(stderr, "wx=%f, wy=%f, rx=%f, ry=%f\n",
               white_x, white_y, red_x, red_y);
            fprintf(stderr, "gx=%f, gy=%f, bx=%f, by=%f\n",
               green_x, green_y, blue_x, blue_y);
#else
            fprintf(stderr, "wx=%ld, wy=%ld, rx=%ld, ry=%ld\n",
               int_x_white, int_y_white, int_x_red, int_y_red);
            fprintf(stderr, "gx=%ld, gy=%ld, bx=%ld, by=%ld\n",
               int_x_green, int_y_green, int_x_blue, int_y_blue);
#endif
#endif /* PNG_NO_CONSOLE_IO */
         }
         return;
      }
#endif /* PNG_READ_sRGB_SUPPORTED */

#ifdef PNG_FLOATING_POINT_SUPPORTED
   png_set_cHRM(png_ptr, info_ptr,
      white_x, white_y, red_x, red_y, green_x, green_y, blue_x, blue_y);
#endif
#ifdef PNG_FIXED_POINT_SUPPORTED
   png_set_cHRM_fixed(png_ptr, info_ptr,
      int_x_white, int_y_white, int_x_red, int_y_red, int_x_green,
      int_y_green, int_x_blue, int_y_blue);
#endif
}
#endif

#if defined(PNG_READ_sRGB_SUPPORTED)
void /* PRIVATE */
png_handle_sRGB(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   int intent;
   png_byte buf[1];

   png_debug(1, "in png_handle_sRGB");

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before sRGB");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid sRGB 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 sRGB chunk");

   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_sRGB))
   {
      png_warning(png_ptr, "Duplicate sRGB chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (length != 1)
   {
      png_warning(png_ptr, "Incorrect sRGB chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, 1);
   if (png_crc_finish(png_ptr, 0))
      return;

   intent = buf[0];
   /* check for bad intent */
   if (intent >= PNG_sRGB_INTENT_LAST)
   {
      png_warning(png_ptr, "Unknown sRGB intent");
      return;
   }

#if defined(PNG_READ_gAMA_SUPPORTED) && defined(PNG_READ_GAMMA_SUPPORTED)
   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_gAMA))
   {
   png_fixed_point igamma;
#ifdef PNG_FIXED_POINT_SUPPORTED
      igamma=info_ptr->int_gamma;
#else
#  ifdef PNG_FLOATING_POINT_SUPPORTED
      igamma=(png_fixed_point)(info_ptr->gamma * 100000.);
#  endif
#endif
      if (PNG_OUT_OF_RANGE(igamma, 45500L, 500))
      {
         png_warning(png_ptr,
           "Ignoring incorrect gAMA value when sRGB is also present");
#ifndef PNG_NO_CONSOLE_IO
#  ifdef PNG_FIXED_POINT_SUPPORTED
         fprintf(stderr, "incorrect gamma=(%d/100000)\n",
            (int)png_ptr->int_gamma);
#  else
#    ifdef PNG_FLOATING_POINT_SUPPORTED
         fprintf(stderr, "incorrect gamma=%f\n", png_ptr->gamma);
#    endif
#  endif
#endif
      }
   }
#endif /* PNG_READ_gAMA_SUPPORTED */

#ifdef PNG_READ_cHRM_SUPPORTED
#ifdef PNG_FIXED_POINT_SUPPORTED
   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_cHRM))
      if (PNG_OUT_OF_RANGE(info_ptr->int_x_white, 31270,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->int_y_white, 32900,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->int_x_red,   64000L, 1000) ||
          PNG_OUT_OF_RANGE(info_ptr->int_y_red,   33000,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->int_x_green, 30000,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->int_y_green, 60000L, 1000) ||
          PNG_OUT_OF_RANGE(info_ptr->int_x_blue,  15000,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->int_y_blue,   6000,  1000))
         {
            png_warning(png_ptr,
              "Ignoring incorrect cHRM value when sRGB is also present");
         }
#endif /* PNG_FIXED_POINT_SUPPORTED */
#endif /* PNG_READ_cHRM_SUPPORTED */

   png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr, intent);
}
#endif /* PNG_READ_sRGB_SUPPORTED */

#if defined(PNG_READ_iCCP_SUPPORTED)
void /* PRIVATE */
png_handle_iCCP(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
/* Note: this does not properly handle chunks that are > 64K under DOS */
{
   png_byte compression_type;
   png_bytep pC;
   png_charp profile;
   png_uint_32 skip = 0;
   png_uint_32 profile_size, profile_length;
   png_size_t slength, prefix_length, data_length;

   png_debug(1, "in png_handle_iCCP");

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before iCCP");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid iCCP 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 iCCP chunk");

   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_iCCP))
   {
      png_warning(png_ptr, "Duplicate iCCP chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

#ifdef PNG_MAX_MALLOC_64K
   if (length > (png_uint_32)65535L)
   {
      png_warning(png_ptr, "iCCP chunk too large to fit in memory");
      skip = length - (png_uint_32)65535L;
      length = (png_uint_32)65535L;
   }
#endif

   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = (png_charp)png_malloc(png_ptr, length + 1);
   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)png_ptr->chunkdata, slength);

   if (png_crc_finish(png_ptr, skip))
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   png_ptr->chunkdata[slength] = 0x00;

   for (profile = png_ptr->chunkdata; *profile; profile++)
      /* empty loop to find end of name */ ;

   ++profile;

   /* there should be at least one zero (the compression type byte)
      following the separator, and we should be on it  */
   if ( profile >= png_ptr->chunkdata + slength - 1)
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      png_warning(png_ptr, "Malformed iCCP chunk");
      return;
   }

   /* compression_type should always be zero */
   compression_type = *profile++;
   if (compression_type)
   {
      png_warning(png_ptr, "Ignoring nonzero compression type in iCCP chunk");
      compression_type = 0x00;  /* Reset it to zero (libpng-1.0.6 through 1.0.8
                                 wrote nonzero) */
   }

   prefix_length = profile - png_ptr->chunkdata;
   png_decompress_chunk(png_ptr, compression_type,
     slength, prefix_length, &data_length);

   profile_length = data_length - prefix_length;

   if ( prefix_length > data_length || profile_length < 4)
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      png_warning(png_ptr, "Profile size field missing from iCCP chunk");
      return;
   }

   /* Check the profile_size recorded in the first 32 bits of the ICC profile */
   pC = (png_bytep)(png_ptr->chunkdata + prefix_length);
   profile_size = ((*(pC    ))<<24) |
                  ((*(pC + 1))<<16) |
                  ((*(pC + 2))<< 8) |
                  ((*(pC + 3))    );

   if (profile_size < profile_length)
      profile_length = profile_size;

   if (profile_size > profile_length)
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      png_warning(png_ptr, "Ignoring truncated iCCP profile.");
      return;
   }

   png_set_iCCP(png_ptr, info_ptr, png_ptr->chunkdata,
     compression_type, png_ptr->chunkdata + prefix_length, profile_length);
   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = NULL;
}
#endif /* PNG_READ_iCCP_SUPPORTED */

#if defined(PNG_READ_sPLT_SUPPORTED)
void /* PRIVATE */
png_handle_sPLT(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
/* Note: this does not properly handle chunks that are > 64K under DOS */
{
   png_bytep entry_start;
   png_sPLT_t new_palette;
#ifdef PNG_NO_POINTER_INDEXING
   png_sPLT_entryp pp;
#endif
   int data_length, entry_size, i;
   png_uint_32 skip = 0;
   png_size_t slength;

   png_debug(1, "in png_handle_sPLT");

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

#ifdef PNG_MAX_MALLOC_64K
   if (length > (png_uint_32)65535L)
   {
      png_warning(png_ptr, "sPLT chunk too large to fit in memory");
      skip = length - (png_uint_32)65535L;
      length = (png_uint_32)65535L;
   }
#endif

   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = (png_charp)png_malloc(png_ptr, length + 1);
   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)png_ptr->chunkdata, slength);

   if (png_crc_finish(png_ptr, skip))
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   png_ptr->chunkdata[slength] = 0x00;

   for (entry_start = (png_bytep)png_ptr->chunkdata; *entry_start; entry_start++)
      /* empty loop to find end of name */ ;
   ++entry_start;

   /* a sample depth should follow the separator, and we should be on it  */
   if (entry_start > (png_bytep)png_ptr->chunkdata + slength - 2)
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      png_warning(png_ptr, "malformed sPLT chunk");
      return;
   }

   new_palette.depth = *entry_start++;
   entry_size = (new_palette.depth == 8 ? 6 : 10);
   data_length = (slength - (entry_start - (png_bytep)png_ptr->chunkdata));

   /* integrity-check the data length */
   if (data_length % entry_size)
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      png_warning(png_ptr, "sPLT chunk has bad length");
      return;
   }

   new_palette.nentries = (png_int_32) ( data_length / entry_size);
   if ((png_uint_32) new_palette.nentries >
       (png_uint_32) (PNG_SIZE_MAX / png_sizeof(png_sPLT_entry)))
   {
       png_warning(png_ptr, "sPLT chunk too long");
       return;
   }
   new_palette.entries = (png_sPLT_entryp)png_malloc_warn(
       png_ptr, new_palette.nentries * png_sizeof(png_sPLT_entry));
   if (new_palette.entries == NULL)
   {
       png_warning(png_ptr, "sPLT chunk requires too much memory");
       return;
   }

#ifndef PNG_NO_POINTER_INDEXING
   for (i = 0; i < new_palette.nentries; i++)
   {
      png_sPLT_entryp pp = new_palette.entries + i;

      if (new_palette.depth == 8)
      {
          pp->red = *entry_start++;
          pp->green = *entry_start++;
          pp->blue = *entry_start++;
          pp->alpha = *entry_start++;
      }
      else
      {
          pp->red   = png_get_uint_16(entry_start); entry_start += 2;
          pp->green = png_get_uint_16(entry_start); entry_start += 2;
          pp->blue  = png_get_uint_16(entry_start); entry_start += 2;
          pp->alpha = png_get_uint_16(entry_start); entry_start += 2;
      }
      pp->frequency = png_get_uint_16(entry_start); entry_start += 2;
   }
#else
   pp = new_palette.entries;
   for (i = 0; i < new_palette.nentries; i++)
   {

      if (new_palette.depth == 8)
      {
          pp[i].red   = *entry_start++;
          pp[i].green = *entry_start++;
          pp[i].blue  = *entry_start++;
          pp[i].alpha = *entry_start++;
      }
      else
      {
          pp[i].red   = png_get_uint_16(entry_start); entry_start += 2;
          pp[i].green = png_get_uint_16(entry_start); entry_start += 2;
          pp[i].blue  = png_get_uint_16(entry_start); entry_start += 2;
          pp[i].alpha = png_get_uint_16(entry_start); entry_start += 2;
      }
      pp->frequency = png_get_uint_16(entry_start); entry_start += 2;
   }
#endif

   /* discard all chunk data except the name and stash that */
   new_palette.name = png_ptr->chunkdata;

   png_set_sPLT(png_ptr, info_ptr, &new_palette, 1);

   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = NULL;
   png_free(png_ptr, new_palette.entries);
}
#endif /* PNG_READ_sPLT_SUPPORTED */

#if defined(PNG_READ_tRNS_SUPPORTED)
void /* PRIVATE */
png_handle_tRNS(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_byte readbuf[PNG_MAX_PALETTE_LENGTH];

   png_debug(1, "in png_handle_tRNS");

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      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 != NULL && (info_ptr->valid & PNG_INFO_tRNS))
   {
      png_warning(png_ptr, "Duplicate tRNS chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (png_ptr->color_type == PNG_COLOR_TYPE_GRAY)
   {
      png_byte buf[2];

      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 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, (png_size_t)length);
      png_ptr->num_trans = 1;
      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_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");
      }
      if (length > (png_uint_32)png_ptr->num_palette ||
          length > PNG_MAX_PALETTE_LENGTH)
      {
         png_warning(png_ptr, "Incorrect tRNS chunk length");
         png_crc_finish(png_ptr, length);
         return;
      }
      if (length == 0)
      {
         png_warning(png_ptr, "Zero length tRNS chunk");
         png_crc_finish(png_ptr, length);
         return;
      }
      png_crc_read(png_ptr, readbuf, (png_size_t)length);
      png_ptr->num_trans = (png_uint_16)length;
   }
   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))
   {
      png_ptr->num_trans = 0;
      return;
   }

   png_set_tRNS(png_ptr, info_ptr, readbuf, png_ptr->num_trans,
      &(png_ptr->trans_values));
}
#endif

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

   png_debug(1, "in png_handle_bKGD");

   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 != NULL && (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, truelen);
   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];
      if (info_ptr && info_ptr->num_palette)
      {
          if (buf[0] >= info_ptr->num_palette)
          {
             png_warning(png_ptr, "Incorrect bKGD chunk index value");
             return;
          }
          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)) /* GRAY */
   {
      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_set_bKGD(png_ptr, info_ptr, &(png_ptr->background));
}
#endif

#if defined(PNG_READ_hIST_SUPPORTED)
void /* PRIVATE */
png_handle_hIST(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   unsigned int num, i;
   png_uint_16 readbuf[PNG_MAX_PALETTE_LENGTH];

   png_debug(1, "in png_handle_hIST");

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      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 != NULL && (info_ptr->valid & PNG_INFO_hIST))
   {
      png_warning(png_ptr, "Duplicate hIST chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   num = length / 2 ;
   if (num != (unsigned int) png_ptr->num_palette || num >
      (unsigned int) PNG_MAX_PALETTE_LENGTH)
   {
      png_warning(png_ptr, "Incorrect hIST chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   for (i = 0; i < num; i++)
   {
      png_byte buf[2];

      png_crc_read(png_ptr, buf, 2);
      readbuf[i] = png_get_uint_16(buf);
   }

   if (png_crc_finish(png_ptr, 0))
      return;

   png_set_hIST(png_ptr, info_ptr, readbuf);
}
#endif

#if defined(PNG_READ_pHYs_SUPPORTED)
void /* PRIVATE */
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;

   png_debug(1, "in png_handle_pHYs");

   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 != NULL && (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_set_pHYs(png_ptr, info_ptr, res_x, res_y, unit_type);
}
#endif

#if defined(PNG_READ_oFFs_SUPPORTED)
void /* PRIVATE */
png_handle_oFFs(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_byte buf[9];
   png_int_32 offset_x, offset_y;
   int unit_type;

   png_debug(1, "in png_handle_oFFs");

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      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 != NULL && (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_int_32(buf);
   offset_y = png_get_int_32(buf + 4);
   unit_type = buf[8];
   png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y, unit_type);
}
#endif

#if defined(PNG_READ_pCAL_SUPPORTED)
/* read the pCAL chunk (described in the PNG Extensions document) */
void /* PRIVATE */
png_handle_pCAL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_int_32 X0, X1;
   png_byte type, nparams;
   png_charp buf, units, endptr;
   png_charpp params;
   png_size_t slength;
   int i;

   png_debug(1, "in png_handle_pCAL");

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

   png_debug1(2, "Allocating and reading pCAL chunk data (%lu bytes)",
      length + 1);
   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = (png_charp)png_malloc_warn(png_ptr, length + 1);
   if (png_ptr->chunkdata == NULL)
     {
       png_warning(png_ptr, "No memory for pCAL purpose.");
       return;
     }
   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)png_ptr->chunkdata, slength);

   if (png_crc_finish(png_ptr, 0))
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   png_ptr->chunkdata[slength] = 0x00; /* null terminate the last string */

   png_debug(3, "Finding end of pCAL purpose string");
   for (buf = png_ptr->chunkdata; *buf; buf++)
      /* empty loop */ ;

   endptr = png_ptr->chunkdata + slength;

   /* We need to have at least 12 bytes after the purpose string
      in order to get the parameter information. */
   if (endptr <= buf + 12)
   {
      png_warning(png_ptr, "Invalid pCAL data");
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   png_debug(3, "Reading pCAL X0, X1, type, nparams, and units");
   X0 = png_get_int_32((png_bytep)buf+1);
   X1 = png_get_int_32((png_bytep)buf+5);
   type = buf[9];
   nparams = buf[10];
   units = buf + 11;

   png_debug(3, "Checking pCAL equation type and number of parameters");
   /* Check that we have the right number of parameters for known
      equation types. */
   if ((type == PNG_EQUATION_LINEAR && nparams != 2) ||
       (type == PNG_EQUATION_BASE_E && nparams != 3) ||
       (type == PNG_EQUATION_ARBITRARY && nparams != 3) ||
       (type == PNG_EQUATION_HYPERBOLIC && nparams != 4))
   {
      png_warning(png_ptr, "Invalid pCAL parameters for equation type");
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }
   else if (type >= PNG_EQUATION_LAST)
   {
      png_warning(png_ptr, "Unrecognized equation type for pCAL chunk");
   }

   for (buf = units; *buf; buf++)
      /* Empty loop to move past the units string. */ ;

   png_debug(3, "Allocating pCAL parameters array");
   params = (png_charpp)png_malloc_warn(png_ptr,
      (png_uint_32)(nparams * png_sizeof(png_charp))) ;
   if (params == NULL)
     {
       png_free(png_ptr, png_ptr->chunkdata);
       png_ptr->chunkdata = NULL;
       png_warning(png_ptr, "No memory for pCAL params.");
       return;
     }

   /* Get pointers to the start of each parameter string. */
   for (i = 0; i < (int)nparams; i++)
   {
      buf++; /* Skip the null string terminator from previous parameter. */

      png_debug1(3, "Reading pCAL parameter %d", i);
      for (params[i] = buf; buf <= endptr && *buf != 0x00; buf++)
         /* Empty loop to move past each parameter string */ ;

      /* Make sure we haven't run out of data yet */
      if (buf > endptr)
      {
         png_warning(png_ptr, "Invalid pCAL data");
         png_free(png_ptr, png_ptr->chunkdata);
         png_ptr->chunkdata = NULL;
         png_free(png_ptr, params);
         return;
      }
   }

   png_set_pCAL(png_ptr, info_ptr, png_ptr->chunkdata, X0, X1, type, nparams,
      units, params);

   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = NULL;
   png_free(png_ptr, params);
}
#endif

#if defined(PNG_READ_sCAL_SUPPORTED)
/* read the sCAL chunk */
void /* PRIVATE */
png_handle_sCAL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_charp ep;
#ifdef PNG_FLOATING_POINT_SUPPORTED
   double width, height;
   png_charp vp;
#else
#ifdef PNG_FIXED_POINT_SUPPORTED
   png_charp swidth, sheight;
#endif
#endif
   png_size_t slength;

   png_debug(1, "in png_handle_sCAL");

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

   png_debug1(2, "Allocating and reading sCAL chunk data (%lu bytes)",
      length + 1);
   png_ptr->chunkdata = (png_charp)png_malloc_warn(png_ptr, length + 1);
   if (png_ptr->chunkdata == NULL)
   {
      png_warning(png_ptr, "Out of memory while processing sCAL chunk");
      return;
   }
   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)png_ptr->chunkdata, slength);

   if (png_crc_finish(png_ptr, 0))
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   png_ptr->chunkdata[slength] = 0x00; /* null terminate the last string */

   ep = png_ptr->chunkdata + 1;        /* skip unit byte */

#ifdef PNG_FLOATING_POINT_SUPPORTED
   width = png_strtod(png_ptr, ep, &vp);
   if (*vp)
   {
      png_warning(png_ptr, "malformed width string in sCAL chunk");
      return;
   }
#else
#ifdef PNG_FIXED_POINT_SUPPORTED
   swidth = (png_charp)png_malloc_warn(png_ptr, png_strlen(ep) + 1);
   if (swidth == NULL)
   {
      png_warning(png_ptr, "Out of memory while processing sCAL chunk width");
      return;
   }
   png_memcpy(swidth, ep, (png_size_t)png_strlen(ep));
#endif
#endif

   for (ep = png_ptr->chunkdata; *ep; ep++)
      /* empty loop */ ;
   ep++;

   if (png_ptr->chunkdata + slength < ep)
   {
      png_warning(png_ptr, "Truncated sCAL chunk");
#if defined(PNG_FIXED_POINT_SUPPORTED) && \
    !defined(PNG_FLOATING_POINT_SUPPORTED)
      png_free(png_ptr, swidth);
#endif
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

#ifdef PNG_FLOATING_POINT_SUPPORTED
   height = png_strtod(png_ptr, ep, &vp);
   if (*vp)
   {
      png_warning(png_ptr, "malformed height string in sCAL chunk");
      return;
   }
#else
#ifdef PNG_FIXED_POINT_SUPPORTED
   sheight = (png_charp)png_malloc_warn(png_ptr, png_strlen(ep) + 1);
   if (sheight == NULL)
   {
      png_warning(png_ptr, "Out of memory while processing sCAL chunk height");
      return;
   }
   png_memcpy(sheight, ep, (png_size_t)png_strlen(ep));
#endif
#endif

   if (png_ptr->chunkdata + slength < ep
#ifdef PNG_FLOATING_POINT_SUPPORTED
      || width <= 0. || height <= 0.
#endif
      )
   {
      png_warning(png_ptr, "Invalid sCAL data");
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
#if defined(PNG_FIXED_POINT_SUPPORTED) && !defined(PNG_FLOATING_POINT_SUPPORTED)
      png_free(png_ptr, swidth);
      png_free(png_ptr, sheight);
#endif
      return;
   }


#ifdef PNG_FLOATING_POINT_SUPPORTED
   png_set_sCAL(png_ptr, info_ptr, png_ptr->chunkdata[0], width, height);
#else
#ifdef PNG_FIXED_POINT_SUPPORTED
   png_set_sCAL_s(png_ptr, info_ptr, png_ptr->chunkdata[0], swidth, sheight);
#endif
#endif

   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = NULL;
#if defined(PNG_FIXED_POINT_SUPPORTED) && !defined(PNG_FLOATING_POINT_SUPPORTED)
   png_free(png_ptr, swidth);
   png_free(png_ptr, sheight);
#endif
}
#endif

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

   png_debug(1, "in png_handle_tIME");

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Out of place tIME chunk");
   else if (info_ptr != NULL && (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_set_tIME(png_ptr, info_ptr, &mod_time);
}
#endif

#if defined(PNG_READ_tEXt_SUPPORTED)
/* Note: this does not properly handle chunks that are > 64K under DOS */
void /* PRIVATE */
png_handle_tEXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_textp text_ptr;
   png_charp key;
   png_charp text;
   png_uint_32 skip = 0;
   png_size_t slength;
   int ret;

   png_debug(1, "in png_handle_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;

#ifdef PNG_MAX_MALLOC_64K
   if (length > (png_uint_32)65535L)
   {
      png_warning(png_ptr, "tEXt chunk too large to fit in memory");
      skip = length - (png_uint_32)65535L;
      length = (png_uint_32)65535L;
   }
#endif

   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = (png_charp)png_malloc_warn(png_ptr, length + 1);
   if (png_ptr->chunkdata == NULL)
   {
     png_warning(png_ptr, "No memory to process text chunk.");
     return;
   }
   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)png_ptr->chunkdata, slength);

   if (png_crc_finish(png_ptr, skip))
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   key = png_ptr->chunkdata;
   key[slength] = 0x00;

   for (text = key; *text; text++)
      /* empty loop to find end of key */ ;

   if (text != key + slength)
      text++;

   text_ptr = (png_textp)png_malloc_warn(png_ptr,
      (png_uint_32)png_sizeof(png_text));
   if (text_ptr == NULL)
   {
     png_warning(png_ptr, "Not enough memory to process text chunk.");
     png_free(png_ptr, png_ptr->chunkdata);
     png_ptr->chunkdata = NULL;
     return;
   }
   text_ptr->compression = PNG_TEXT_COMPRESSION_NONE;
   text_ptr->key = key;
#ifdef PNG_iTXt_SUPPORTED
   text_ptr->lang = NULL;
   text_ptr->lang_key = NULL;
   text_ptr->itxt_length = 0;
#endif
   text_ptr->text = text;
   text_ptr->text_length = png_strlen(text);

   ret = png_set_text_2(png_ptr, info_ptr, text_ptr, 1);

   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = NULL;
   png_free(png_ptr, text_ptr);
   if (ret)
     png_warning(png_ptr, "Insufficient memory to process text chunk.");
}
#endif

#if defined(PNG_READ_zTXt_SUPPORTED)
/* note: this does not correctly handle chunks that are > 64K under DOS */
void /* PRIVATE */
png_handle_zTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_textp text_ptr;
   png_charp text;
   int comp_type;
   int ret;
   png_size_t slength, prefix_len, data_len;

   png_debug(1, "in png_handle_zTXt");
   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;

#ifdef PNG_MAX_MALLOC_64K
   /* We will no doubt have problems with chunks even half this size, but
      there is no hard and fast rule to tell us where to stop. */
   if (length > (png_uint_32)65535L)
   {
     png_warning(png_ptr, "zTXt chunk too large to fit in memory");
     png_crc_finish(png_ptr, length);
     return;
   }
#endif

   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = (png_charp)png_malloc_warn(png_ptr, length + 1);
   if (png_ptr->chunkdata == NULL)
   {
     png_warning(png_ptr, "Out of memory processing zTXt chunk.");
     return;
   }
   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)png_ptr->chunkdata, slength);
   if (png_crc_finish(png_ptr, 0))
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   png_ptr->chunkdata[slength] = 0x00;

   for (text = png_ptr->chunkdata; *text; text++)
      /* empty loop */ ;

   /* zTXt must have some text after the chunkdataword */
   if (text >= png_ptr->chunkdata + slength - 2)
   {
      png_warning(png_ptr, "Truncated zTXt chunk");
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }
   else
   {
       comp_type = *(++text);
       if (comp_type != PNG_TEXT_COMPRESSION_zTXt)
       {
          png_warning(png_ptr, "Unknown compression type in zTXt chunk");
          comp_type = PNG_TEXT_COMPRESSION_zTXt;
       }
       text++;        /* skip the compression_method byte */
   }
   prefix_len = text - png_ptr->chunkdata;

   png_decompress_chunk(png_ptr, comp_type,
     (png_size_t)length, prefix_len, &data_len);

   text_ptr = (png_textp)png_malloc_warn(png_ptr,
      (png_uint_32)png_sizeof(png_text));
   if (text_ptr == NULL)
   {
     png_warning(png_ptr, "Not enough memory to process zTXt chunk.");
     png_free(png_ptr, png_ptr->chunkdata);
     png_ptr->chunkdata = NULL;
     return;
   }
   text_ptr->compression = comp_type;
   text_ptr->key = png_ptr->chunkdata;
#ifdef PNG_iTXt_SUPPORTED
   text_ptr->lang = NULL;
   text_ptr->lang_key = NULL;
   text_ptr->itxt_length = 0;
#endif
   text_ptr->text = png_ptr->chunkdata + prefix_len;
   text_ptr->text_length = data_len;

   ret = png_set_text_2(png_ptr, info_ptr, text_ptr, 1);

   png_free(png_ptr, text_ptr);
   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = NULL;
   if (ret)
     png_error(png_ptr, "Insufficient memory to store zTXt chunk.");
}
#endif

#if defined(PNG_READ_iTXt_SUPPORTED)
/* note: this does not correctly handle chunks that are > 64K under DOS */
void /* PRIVATE */
png_handle_iTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_textp text_ptr;
   png_charp key, lang, text, lang_key;
   int comp_flag;
   int comp_type = 0;
   int ret;
   png_size_t slength, prefix_len, data_len;

   png_debug(1, "in png_handle_iTXt");

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

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

#ifdef PNG_MAX_MALLOC_64K
   /* We will no doubt have problems with chunks even half this size, but
      there is no hard and fast rule to tell us where to stop. */
   if (length > (png_uint_32)65535L)
   {
     png_warning(png_ptr, "iTXt chunk too large to fit in memory");
     png_crc_finish(png_ptr, length);
     return;
   }
#endif

   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = (png_charp)png_malloc_warn(png_ptr, length + 1);
   if (png_ptr->chunkdata == NULL)
   {
     png_warning(png_ptr, "No memory to process iTXt chunk.");
     return;
   }
   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)png_ptr->chunkdata, slength);
   if (png_crc_finish(png_ptr, 0))
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   png_ptr->chunkdata[slength] = 0x00;

   for (lang = png_ptr->chunkdata; *lang; lang++)
      /* empty loop */ ;
   lang++;        /* skip NUL separator */

   /* iTXt must have a language tag (possibly empty), two compression bytes,
      translated keyword (possibly empty), and possibly some text after the
      keyword */

   if (lang >= png_ptr->chunkdata + slength - 3)
   {
      png_warning(png_ptr, "Truncated iTXt chunk");
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }
   else
   {
       comp_flag = *lang++;
       comp_type = *lang++;
   }

   for (lang_key = lang; *lang_key; lang_key++)
      /* empty loop */ ;
   lang_key++;        /* skip NUL separator */

   if (lang_key >= png_ptr->chunkdata + slength)
   {
      png_warning(png_ptr, "Truncated iTXt chunk");
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   for (text = lang_key; *text; text++)
      /* empty loop */ ;
   text++;        /* skip NUL separator */
   if (text >= png_ptr->chunkdata + slength)
   {
      png_warning(png_ptr, "Malformed iTXt chunk");
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   prefix_len = text - png_ptr->chunkdata;

   key=png_ptr->chunkdata;
   if (comp_flag)
       png_decompress_chunk(png_ptr, comp_type,
         (size_t)length, prefix_len, &data_len);
   else
       data_len = png_strlen(png_ptr->chunkdata + prefix_len);
   text_ptr = (png_textp)png_malloc_warn(png_ptr,
      (png_uint_32)png_sizeof(png_text));
   if (text_ptr == NULL)
   {
     png_warning(png_ptr, "Not enough memory to process iTXt chunk.");
     png_free(png_ptr, png_ptr->chunkdata);
     png_ptr->chunkdata = NULL;
     return;
   }
   text_ptr->compression = (int)comp_flag + 1;
   text_ptr->lang_key = png_ptr->chunkdata + (lang_key - key);
   text_ptr->lang = png_ptr->chunkdata + (lang - key);
   text_ptr->itxt_length = data_len;
   text_ptr->text_length = 0;
   text_ptr->key = png_ptr->chunkdata;
   text_ptr->text = png_ptr->chunkdata + prefix_len;

   ret = png_set_text_2(png_ptr, info_ptr, text_ptr, 1);

   png_free(png_ptr, text_ptr);
   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = NULL;
   if (ret)
     png_error(png_ptr, "Insufficient memory to store iTXt chunk.");
}
#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, CRC, or a critical chunk), the chunk is silently ignored
   -- unless the PNG_FLAG_UNKNOWN_CHUNKS_SUPPORTED flag is on in which
   case it will be saved away to be written out later. */
void /* PRIVATE */
png_handle_unknown(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_uint_32 skip = 0;

   png_debug(1, "in png_handle_unknown");

   if (png_ptr->mode & PNG_HAVE_IDAT)
   {
#ifdef PNG_USE_LOCAL_ARRAYS
      PNG_CONST PNG_IDAT;
#endif
      if (png_memcmp(png_ptr->chunk_name, png_IDAT, 4))  /* not an IDAT */
         png_ptr->mode |= PNG_AFTER_IDAT;
   }

   if (!(png_ptr->chunk_name[0] & 0x20))
   {
#if defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
      if (png_handle_as_unknown(png_ptr, png_ptr->chunk_name) !=
           PNG_HANDLE_CHUNK_ALWAYS
#if defined(PNG_READ_USER_CHUNKS_SUPPORTED)
           && png_ptr->read_user_chunk_fn == NULL
#endif
        )
#endif
          png_chunk_error(png_ptr, "unknown critical chunk");
   }

#if defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
   if ((png_ptr->flags & PNG_FLAG_KEEP_UNKNOWN_CHUNKS) ||
       (png_ptr->read_user_chunk_fn != NULL))
   {
#ifdef PNG_MAX_MALLOC_64K
       if (length > (png_uint_32)65535L)
       {
           png_warning(png_ptr, "unknown chunk too large to fit in memory");
           skip = length - (png_uint_32)65535L;
           length = (png_uint_32)65535L;
       }
#endif
       png_memcpy((png_charp)png_ptr->unknown_chunk.name,
                  (png_charp)png_ptr->chunk_name, 
                  png_sizeof(png_ptr->unknown_chunk.name));
       png_ptr->unknown_chunk.name[png_sizeof(png_ptr->unknown_chunk.name)-1] = '\0';
       png_ptr->unknown_chunk.size = (png_size_t)length;
       if (length == 0)
         png_ptr->unknown_chunk.data = NULL;
       else
       {
         png_ptr->unknown_chunk.data = (png_bytep)png_malloc(png_ptr, length);
         png_crc_read(png_ptr, (png_bytep)png_ptr->unknown_chunk.data, length);
       }
#if defined(PNG_READ_USER_CHUNKS_SUPPORTED)
       if (png_ptr->read_user_chunk_fn != NULL)
       {
          /* callback to user unknown chunk handler */
          int ret;
          ret = (*(png_ptr->read_user_chunk_fn))
            (png_ptr, &png_ptr->unknown_chunk);
          if (ret < 0)
             png_chunk_error(png_ptr, "error in user chunk");
          if (ret == 0)
          {
             if (!(png_ptr->chunk_name[0] & 0x20))
                if (png_handle_as_unknown(png_ptr, png_ptr->chunk_name) !=
                     PNG_HANDLE_CHUNK_ALWAYS)
                   png_chunk_error(png_ptr, "unknown critical chunk");
             png_set_unknown_chunks(png_ptr, info_ptr,
               &png_ptr->unknown_chunk, 1);
          }
       }
       else
#endif
       png_set_unknown_chunks(png_ptr, info_ptr, &png_ptr->unknown_chunk, 1);
       png_free(png_ptr, png_ptr->unknown_chunk.data);
       png_ptr->unknown_chunk.data = NULL;
   }
   else
#endif
      skip = length;

   png_crc_finish(png_ptr, skip);

#if !defined(PNG_READ_USER_CHUNKS_SUPPORTED)
   info_ptr = info_ptr; /* quiet compiler warnings about unused info_ptr */
#endif
}

/* This function is called to verify that a chunk name is valid.
   This function can't have the "critical chunk check" incorporated
   into it, since in the future we will need to be able to call user
   functions to handle unknown critical chunks after we check that
   the chunk name itself is valid. */

#define isnonalpha(c) ((c) < 65 || (c) > 122 || ((c) > 90 && (c) < 97))

void /* PRIVATE */
png_check_chunk_name(png_structp png_ptr, png_bytep chunk_name)
{
   png_debug(1, "in png_check_chunk_name");
   if (isnonalpha(chunk_name[0]) || isnonalpha(chunk_name[1]) ||
       isnonalpha(chunk_name[2]) || isnonalpha(chunk_name[3]))
   {
      png_chunk_error(png_ptr, "invalid chunk type");
   }
}

/* Combines the row recently read in with the existing pixels in the
   row.  This routine takes care of alpha and transparency if requested.
   This routine also handles the two methods of progressive display
   of interlaced images, depending on the 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 pixel 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 /* PRIVATE */
png_combine_row(png_structp png_ptr, png_bytep row, int mask)
{
   png_debug(1, "in png_combine_row");
   if (mask == 0xff)
   {
      png_memcpy(row, png_ptr->row_buf + 1,
         PNG_ROWBYTES(png_ptr->row_info.pixel_depth, png_ptr->width));
   }
   else
   {
      switch (png_ptr->row_info.pixel_depth)
      {
         case 1:
         {
            png_bytep sp = png_ptr->row_buf + 1;
            png_bytep dp = row;
            int s_inc, s_start, s_end;
            int m = 0x80;
            int shift;
            png_uint_32 i;
            png_uint_32 row_width = png_ptr->width;

#if defined(PNG_READ_PACKSWAP_SUPPORTED)
            if (png_ptr->transformations & PNG_PACKSWAP)
            {
                s_start = 0;
                s_end = 7;
                s_inc = 1;
            }
            else
#endif
            {
                s_start = 7;
                s_end = 0;
                s_inc = -1;
            }

            shift = s_start;

            for (i = 0; i < row_width; i++)
            {
               if (m & mask)
               {
                  int value;

                  value = (*sp >> shift) & 0x01;
                  *dp &= (png_byte)((0x7f7f >> (7 - shift)) & 0xff);
                  *dp |= (png_byte)(value << shift);
               }

               if (shift == s_end)
               {
                  shift = s_start;
                  sp++;
                  dp++;
               }
               else
                  shift += s_inc;

               if (m == 1)
                  m = 0x80;
               else
                  m >>= 1;
            }
            break;
         }
         case 2:
         {
            png_bytep sp = png_ptr->row_buf + 1;
            png_bytep dp = row;
            int s_start, s_end, s_inc;
            int m = 0x80;
            int shift;
            png_uint_32 i;
            png_uint_32 row_width = png_ptr->width;
            int value;

#if defined(PNG_READ_PACKSWAP_SUPPORTED)
            if (png_ptr->transformations & PNG_PACKSWAP)
            {
               s_start = 0;
               s_end = 6;
               s_inc = 2;
            }
            else
#endif
            {
               s_start = 6;
               s_end = 0;
               s_inc = -2;
            }

            shift = s_start;

            for (i = 0; i < row_width; i++)
            {
               if (m & mask)
               {
                  value = (*sp >> shift) & 0x03;
                  *dp &= (png_byte)((0x3f3f >> (6 - shift)) & 0xff);
                  *dp |= (png_byte)(value << shift);
               }

               if (shift == s_end)
               {
                  shift = s_start;
                  sp++;
                  dp++;
               }
               else
                  shift += s_inc;
               if (m == 1)
                  m = 0x80;
               else
                  m >>= 1;
            }
            break;
         }
         case 4:
         {
            png_bytep sp = png_ptr->row_buf + 1;
            png_bytep dp = row;
            int s_start, s_end, s_inc;
            int m = 0x80;
            int shift;
            png_uint_32 i;
            png_uint_32 row_width = png_ptr->width;
            int value;

#if defined(PNG_READ_PACKSWAP_SUPPORTED)
            if (png_ptr->transformations & PNG_PACKSWAP)
            {
               s_start = 0;
               s_end = 4;
               s_inc = 4;
            }
            else
#endif
            {
               s_start = 4;
               s_end = 0;
               s_inc = -4;
            }
            shift = s_start;

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

               if (shift == s_end)
               {
                  shift = s_start;
                  sp++;
                  dp++;
               }
               else
                  shift += s_inc;
               if (m == 1)
                  m = 0x80;
               else
                  m >>= 1;
            }
            break;
         }
         default:
         {
            png_bytep sp = png_ptr->row_buf + 1;
            png_bytep dp = row;
            png_size_t pixel_bytes = (png_ptr->row_info.pixel_depth >> 3);
            png_uint_32 i;
            png_uint_32 row_width = png_ptr->width;
            png_byte m = 0x80;


            for (i = 0; i < row_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;
         }
      }
   }
}

#ifdef PNG_READ_INTERLACING_SUPPORTED
/* OLD pre-1.0.9 interface:
void png_do_read_interlace(png_row_infop row_info, png_bytep row, int pass,
   png_uint_32 transformations)
 */
void /* PRIVATE */
png_do_read_interlace(png_structp png_ptr)
{
   png_row_infop row_info = &(png_ptr->row_info);
   png_bytep row = png_ptr->row_buf + 1;
   int pass = png_ptr->pass;
   png_uint_32 transformations = png_ptr->transformations;
#ifdef PNG_USE_LOCAL_ARRAYS
   /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */
   /* offset to next interlace block */
   PNG_CONST int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
#endif

   png_debug(1, "in png_do_read_interlace");
   if (row != NULL && row_info != NULL)
   {
      png_uint_32 final_width;

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

      switch (row_info->pixel_depth)
      {
         case 1:
         {
            png_bytep sp = row + (png_size_t)((row_info->width - 1) >> 3);
            png_bytep dp = row + (png_size_t)((final_width - 1) >> 3);
            int sshift, dshift;
            int s_start, s_end, s_inc;
            int jstop = png_pass_inc[pass];
            png_byte v;
            png_uint_32 i;
            int j;

#if defined(PNG_READ_PACKSWAP_SUPPORTED)
            if (transformations & PNG_PACKSWAP)
            {
                sshift = (int)((row_info->width + 7) & 0x07);
                dshift = (int)((final_width + 7) & 0x07);
                s_start = 7;
                s_end = 0;
                s_inc = -1;
            }
            else
#endif
            {
                sshift = 7 - (int)((row_info->width + 7) & 0x07);
                dshift = 7 - (int)((final_width + 7) & 0x07);
                s_start = 0;
                s_end = 7;
                s_inc = 1;
            }

            for (i = 0; i < row_info->width; i++)
            {
               v = (png_byte)((*sp >> sshift) & 0x01);
               for (j = 0; j < jstop; j++)
               {
                  *dp &= (png_byte)((0x7f7f >> (7 - dshift)) & 0xff);
                  *dp |= (png_byte)(v << dshift);
                  if (dshift == s_end)
                  {
                     dshift = s_start;
                     dp--;
                  }
                  else
                     dshift += s_inc;
               }
               if (sshift == s_end)
               {
                  sshift = s_start;
                  sp--;
               }
               else
                  sshift += s_inc;
            }
            break;
         }
         case 2:
         {
            png_bytep sp = row + (png_uint_32)((row_info->width - 1) >> 2);
            png_bytep dp = row + (png_uint_32)((final_width - 1) >> 2);
            int sshift, dshift;
            int s_start, s_end, s_inc;
            int jstop = png_pass_inc[pass];
            png_uint_32 i;

#if defined(PNG_READ_PACKSWAP_SUPPORTED)
            if (transformations & PNG_PACKSWAP)
            {
               sshift = (int)(((row_info->width + 3) & 0x03) << 1);
               dshift = (int)(((final_width + 3) & 0x03) << 1);
               s_start = 6;
               s_end = 0;
               s_inc = -2;
            }
            else
#endif
            {
               sshift = (int)((3 - ((row_info->width + 3) & 0x03)) << 1);
               dshift = (int)((3 - ((final_width + 3) & 0x03)) << 1);
               s_start = 0;
               s_end = 6;
               s_inc = 2;
            }

            for (i = 0; i < row_info->width; i++)
            {
               png_byte v;
               int j;

               v = (png_byte)((*sp >> sshift) & 0x03);
               for (j = 0; j < jstop; j++)
               {
                  *dp &= (png_byte)((0x3f3f >> (6 - dshift)) & 0xff);
                  *dp |= (png_byte)(v << dshift);
                  if (dshift == s_end)
                  {
                     dshift = s_start;
                     dp--;
                  }
                  else
                     dshift += s_inc;
               }
               if (sshift == s_end)
               {
                  sshift = s_start;
                  sp--;
               }
               else
                  sshift += s_inc;
            }
            break;
         }
         case 4:
         {
            png_bytep sp = row + (png_size_t)((row_info->width - 1) >> 1);
            png_bytep dp = row + (png_size_t)((final_width - 1) >> 1);
            int sshift, dshift;
            int s_start, s_end, s_inc;
            png_uint_32 i;
            int jstop = png_pass_inc[pass];

#if defined(PNG_READ_PACKSWAP_SUPPORTED)
            if (transformations & PNG_PACKSWAP)
            {
               sshift = (int)(((row_info->width + 1) & 0x01) << 2);
               dshift = (int)(((final_width + 1) & 0x01) << 2);
               s_start = 4;
               s_end = 0;
               s_inc = -4;
            }
            else
#endif
            {
               sshift = (int)((1 - ((row_info->width + 1) & 0x01)) << 2);
               dshift = (int)((1 - ((final_width + 1) & 0x01)) << 2);
               s_start = 0;
               s_end = 4;
               s_inc = 4;
            }

            for (i = 0; i < row_info->width; i++)
            {
               png_byte v = (png_byte)((*sp >> sshift) & 0xf);
               int j;

               for (j = 0; j < jstop; j++)
               {
                  *dp &= (png_byte)((0xf0f >> (4 - dshift)) & 0xff);
                  *dp |= (png_byte)(v << dshift);
                  if (dshift == s_end)
                  {
                     dshift = s_start;
                     dp--;
                  }
                  else
                     dshift += s_inc;
               }
               if (sshift == s_end)
               {
                  sshift = s_start;
                  sp--;
               }
               else
                  sshift += s_inc;
            }
            break;
         }
         default:
         {
            png_size_t pixel_bytes = (row_info->pixel_depth >> 3);
            png_bytep sp = row + (png_size_t)(row_info->width - 1) * pixel_bytes;
            png_bytep dp = row + (png_size_t)(final_width - 1) * pixel_bytes;

            int jstop = png_pass_inc[pass];
            png_uint_32 i;

            for (i = 0; i < row_info->width; i++)
            {
               png_byte v[8];
               int j;

               png_memcpy(v, sp, pixel_bytes);
               for (j = 0; j < jstop; j++)
               {
                  png_memcpy(dp, v, pixel_bytes);
                  dp -= pixel_bytes;
               }
               sp -= pixel_bytes;
            }
            break;
         }
      }
      row_info->width = final_width;
      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, final_width);
   }
#if !defined(PNG_READ_PACKSWAP_SUPPORTED)
   transformations = transformations; /* silence compiler warning */
#endif
}
#endif /* PNG_READ_INTERLACING_SUPPORTED */

void /* PRIVATE */
png_read_filter_row(png_structp png_ptr, png_row_infop row_info, png_bytep row,
   png_bytep prev_row, int filter)
{
   png_debug(1, "in png_read_filter_row");
   png_debug2(2, "row = %lu, filter = %d", png_ptr->row_number, filter);
   switch (filter)
   {
      case PNG_FILTER_VALUE_NONE:
         break;
      case PNG_FILTER_VALUE_SUB:
      {
         png_uint_32 i;
         png_uint_32 istop = row_info->rowbytes;
         png_uint_32 bpp = (row_info->pixel_depth + 7) >> 3;
         png_bytep rp = row + bpp;
         png_bytep lp = row;

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

         for (i = 0; i < istop; i++)
         {
            *rp = (png_byte)(((int)(*rp) + (int)(*pp++)) & 0xff);
            rp++;
         }
         break;
      }
      case PNG_FILTER_VALUE_AVG:
      {
         png_uint_32 i;
         png_bytep rp = row;
         png_bytep pp = prev_row;
         png_bytep lp = row;
         png_uint_32 bpp = (row_info->pixel_depth + 7) >> 3;
         png_uint_32 istop = row_info->rowbytes - bpp;

         for (i = 0; i < bpp; i++)
         {
            *rp = (png_byte)(((int)(*rp) +
               ((int)(*pp++) / 2 )) & 0xff);
            rp++;
         }

         for (i = 0; i < istop; i++)
         {
            *rp = (png_byte)(((int)(*rp) +
               (int)(*pp++ + *lp++) / 2 ) & 0xff);
            rp++;
         }
         break;
      }
      case PNG_FILTER_VALUE_PAETH:
      {
         png_uint_32 i;
         png_bytep rp = row;
         png_bytep pp = prev_row;
         png_bytep lp = row;
         png_bytep cp = prev_row;
         png_uint_32 bpp = (row_info->pixel_depth + 7) >> 3;
         png_uint_32 istop=row_info->rowbytes - bpp;

         for (i = 0; i < bpp; i++)
         {
            *rp = (png_byte)(((int)(*rp) + (int)(*pp++)) & 0xff);
            rp++;
         }

         for (i = 0; i < istop; i++)   /* use leftover rp,pp */
         {
            int a, b, c, pa, pb, pc, p;

            a = *lp++;
            b = *pp++;
            c = *cp++;

            p = b - c;
            pc = a - c;

#ifdef PNG_USE_ABS
            pa = abs(p);
            pb = abs(pc);
            pc = abs(p + pc);
#else
            pa = p < 0 ? -p : p;
            pb = pc < 0 ? -pc : pc;
            pc = (p + pc) < 0 ? -(p + pc) : p + pc;
#endif

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

            p = (pa <= pb && pa <= pc) ? a : (pb <= pc) ? b : c;

            *rp = (png_byte)(((int)(*rp) + p) & 0xff);
            rp++;
         }
         break;
      }
      default:
         png_warning(png_ptr, "Ignoring bad adaptive filter type");
         *row = 0;
         break;
   }
}

void /* PRIVATE */
png_read_finish_row(png_structp png_ptr)
{
#ifdef PNG_USE_LOCAL_ARRAYS
#ifdef PNG_READ_INTERLACING_SUPPORTED
   /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */

   /* start of interlace block */
   PNG_CONST int png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};

   /* offset to next interlace block */
   PNG_CONST int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};

   /* start of interlace block in the y direction */
   PNG_CONST int png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};

   /* offset to next interlace block in the y direction */
   PNG_CONST int png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
#endif /* PNG_READ_INTERLACING_SUPPORTED */
#endif

   png_debug(1, "in png_read_finish_row");
   png_ptr->row_number++;
   if (png_ptr->row_number < png_ptr->num_rows)
      return;

#ifdef PNG_READ_INTERLACING_SUPPORTED
   if (png_ptr->interlaced)
   {
      png_ptr->row_number = 0;
      png_memset_check(png_ptr, png_ptr->prev_row, 0,
         png_ptr->rowbytes + 1);
      do
      {
         png_ptr->pass++;
         if (png_ptr->pass >= 7)
            break;
         png_ptr->iwidth = (png_ptr->width +
            png_pass_inc[png_ptr->pass] - 1 -
            png_pass_start[png_ptr->pass]) /
            png_pass_inc[png_ptr->pass];

         png_ptr->irowbytes = PNG_ROWBYTES(png_ptr->pixel_depth,
            png_ptr->iwidth) + 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;
         }
         else  /* if (png_ptr->transformations & PNG_INTERLACE) */
            break;
      } while (png_ptr->iwidth == 0);

      if (png_ptr->pass < 7)
         return;
   }
#endif /* PNG_READ_INTERLACING_SUPPORTED */

   if (!(png_ptr->flags & PNG_FLAG_ZLIB_FINISHED))
   {
#ifdef PNG_USE_LOCAL_ARRAYS
      PNG_CONST PNG_IDAT;
#endif
      char extra;
      int ret;

      png_ptr->zstream.next_out = (Byte *)&extra;
      png_ptr->zstream.avail_out = (uInt)1;
      for (;;)
      {
         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_31(png_ptr, 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_warning(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_warning(png_ptr, "Extra compressed data.");
            png_ptr->mode |= PNG_AFTER_IDAT;
            png_ptr->flags |= PNG_FLAG_ZLIB_FINISHED;
            break;
         }

      }
      png_ptr->zstream.avail_out = 0;
   }

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

   inflateReset(&png_ptr->zstream);

   png_ptr->mode |= PNG_AFTER_IDAT;
}

void /* PRIVATE */
png_read_start_row(png_structp png_ptr)
{
#ifdef PNG_USE_LOCAL_ARRAYS
#ifdef PNG_READ_INTERLACING_SUPPORTED
   /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */

   /* start of interlace block */
   PNG_CONST int png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};

   /* offset to next interlace block */
   PNG_CONST int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};

   /* start of interlace block in the y direction */
   PNG_CONST int png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};

   /* offset to next interlace block in the y direction */
   PNG_CONST int png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
#endif
#endif

   int max_pixel_depth;
   png_size_t row_bytes;

   png_debug(1, "in png_read_start_row");
   png_ptr->zstream.avail_in = 0;
   png_init_read_transformations(png_ptr);
#ifdef PNG_READ_INTERLACING_SUPPORTED
   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_ROWBYTES(png_ptr->pixel_depth, png_ptr->iwidth) + 1;
   }
   else
#endif /* PNG_READ_INTERLACING_SUPPORTED */
   {
      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 (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
         max_pixel_depth = 32;
      else if (png_ptr->color_type == PNG_COLOR_TYPE_GRAY)
      {
         if (max_pixel_depth <= 8)
            max_pixel_depth = 16;
         else
            max_pixel_depth = 32;
      }
      else if (png_ptr->color_type == PNG_COLOR_TYPE_RGB)
      {
         if (max_pixel_depth <= 32)
            max_pixel_depth = 32;
         else
            max_pixel_depth = 64;
      }
   }
#endif

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

#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) && \
defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
   if (png_ptr->transformations & PNG_USER_TRANSFORM)
     {
       int user_pixel_depth = png_ptr->user_transform_depth*
         png_ptr->user_transform_channels;
       if (user_pixel_depth > max_pixel_depth)
         max_pixel_depth=user_pixel_depth;
     }
#endif

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

   if (row_bytes + 64 > png_ptr->old_big_row_buf_size)
   {
     png_free(png_ptr, png_ptr->big_row_buf);
     png_ptr->big_row_buf = (png_bytep)png_malloc(png_ptr, row_bytes+64);
     png_ptr->row_buf = png_ptr->big_row_buf+32;
     png_ptr->old_big_row_buf_size = row_bytes+64;
   }

#ifdef PNG_MAX_MALLOC_64K
   if ((png_uint_32)png_ptr->rowbytes + 1 > (png_uint_32)65536L)
      png_error(png_ptr, "This image requires a row greater than 64KB");
#endif
   if ((png_uint_32)png_ptr->rowbytes > (png_uint_32)(PNG_SIZE_MAX - 1))
      png_error(png_ptr, "Row has too many bytes to allocate in memory.");

   if (png_ptr->rowbytes+1 > png_ptr->old_prev_row_size)
   {
     png_free(png_ptr, png_ptr->prev_row);
     png_ptr->prev_row = (png_bytep)png_malloc(png_ptr, (png_uint_32)(
        png_ptr->rowbytes + 1));
     png_ptr->old_prev_row_size = png_ptr->rowbytes+1;
   }

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

   png_debug1(3, "width = %lu,", png_ptr->width);
   png_debug1(3, "height = %lu,", png_ptr->height);
   png_debug1(3, "iwidth = %lu,", png_ptr->iwidth);
   png_debug1(3, "num_rows = %lu", png_ptr->num_rows);
   png_debug1(3, "rowbytes = %lu,", png_ptr->rowbytes);
   png_debug1(3, "irowbytes = %lu,", png_ptr->irowbytes);

   png_ptr->flags |= PNG_FLAG_ROW_INIT;
}
#endif /* PNG_READ_SUPPORTED */