pngrutil.c

/* pngrutil.c - utilities to read a PNG file
 *
 * Last changed in libpng 1.5.3 [(PENDING RELEASE)]
 * Copyright (c) 1998-2011 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 code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 *
 * This file contains routines that are only called from within
 * libpng itself during the course of reading an image.
 */

#include "pngpriv.h"

#ifdef PNG_READ_SUPPORTED

#define png_strtod(p,a,b) strtod(a,b)

png_uint_32 PNGAPI
png_get_uint_31(png_structp png_ptr, png_const_bytep buf)
{
   png_uint_32 uval = png_get_uint_32(buf);

   if (uval > PNG_UINT_31_MAX)
      png_error(png_ptr, "PNG unsigned integer out of range");

   return (uval);
}

#if defined(PNG_READ_gAMA_SUPPORTED) || defined(PNG_READ_cHRM_SUPPORTED)
/* The following is a variation on the above for use with the fixed
 * point values used for gAMA and cHRM.  Instead of png_error it
 * issues a warning and returns (-1) - an invalid value because both
 * gAMA and cHRM use *unsigned* integers for fixed point values.
 */
#define PNG_FIXED_ERROR (-1)

static png_fixed_point /* PRIVATE */
png_get_fixed_point(png_structp png_ptr, png_const_bytep buf)
{
   png_uint_32 uval = png_get_uint_32(buf);

   if (uval <= PNG_UINT_31_MAX)
      return (png_fixed_point)uval; /* known to be in range */

   /* The caller can turn off the warning by passing NULL. */
   if (png_ptr != NULL)
      png_warning(png_ptr, "PNG fixed point integer out of range");

   return PNG_FIXED_ERROR;
}
#endif

#ifdef PNG_READ_INT_FUNCTIONS_SUPPORTED
/* NOTE: the read macros will obscure these definitions, so that if
 * PNG_USE_READ_MACROS is set the library will not use them internally,
 * but the APIs will still be available externally.
 *
 * The parentheses around "PNGAPI function_name" in the following three
 * functions are necessary because they allow the macros to co-exist with
 * these (unused but exported) functions.
 */

/* Grab an unsigned 32-bit integer from a buffer in big-endian format. */
png_uint_32 (PNGAPI
png_get_uint_32)(png_const_bytep buf)
{
   png_uint_32 uval =
       ((png_uint_32)(*(buf    )) << 24) +
       ((png_uint_32)(*(buf + 1)) << 16) +
       ((png_uint_32)(*(buf + 2)) <<  8) +
       ((png_uint_32)(*(buf + 3))      ) ;

   return uval;
}

/* Grab a signed 32-bit integer from a buffer in big-endian format.  The
 * data is stored in the PNG file in two's complement format and there
 * is no guarantee that a 'png_int_32' is exactly 32 bits, therefore
 * the following code does a two's complement to native conversion.
 */
png_int_32 (PNGAPI
png_get_int_32)(png_const_bytep buf)
{
   png_uint_32 uval = png_get_uint_32(buf);
   if ((uval & 0x80000000L) == 0) /* non-negative */
      return uval;

   uval = (uval ^ 0xffffffffL) + 1;  /* 2's complement: -x = ~x+1 */
   return -(png_int_32)uval;
}

/* Grab an unsigned 16-bit integer from a buffer in big-endian format. */
png_uint_16 (PNGAPI
png_get_uint_16)(png_const_bytep buf)
{
   /* ANSI-C requires an int value to accomodate at least 16 bits so this
    * works and allows the compiler not to worry about possible narrowing
    * on 32 bit systems.  (Pre-ANSI systems did not make integers smaller
    * than 16 bits either.)
    */
   unsigned int val =
       ((unsigned int)(*buf) << 8) +
       ((unsigned int)(*(buf + 1)));

   return (png_uint_16)val;
}

#endif /* PNG_READ_INT_FUNCTIONS_SUPPORTED */

/* Read and check the PNG file signature */
void /* PRIVATE */
png_read_sig(png_structp png_ptr, png_infop info_ptr)
{
   png_size_t num_checked, num_to_check;

   /* Exit if the user application does not expect a signature. */
   if (png_ptr->sig_bytes >= 8)
      return;

   num_checked = png_ptr->sig_bytes;
   num_to_check = 8 - num_checked;

#ifdef PNG_IO_STATE_SUPPORTED
   png_ptr->io_state = PNG_IO_READING | PNG_IO_SIGNATURE;
#endif

   /* The signature must be serialized in a single I/O call. */
   png_read_data(png_ptr, &(info_ptr->signature[num_checked]), num_to_check);
   png_ptr->sig_bytes = 8;

   if (png_sig_cmp(info_ptr->signature, num_checked, num_to_check))
   {
      if (num_checked < 4 &&
          png_sig_cmp(info_ptr->signature, num_checked, num_to_check - 4))
         png_error(png_ptr, "Not a PNG file");
      else
         png_error(png_ptr, "PNG file corrupted by ASCII conversion");
   }
   if (num_checked < 3)
      png_ptr->mode |= PNG_HAVE_PNG_SIGNATURE;
}

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

#ifdef PNG_IO_STATE_SUPPORTED
   png_ptr->io_state = PNG_IO_READING | PNG_IO_CHUNK_HDR;
#endif

   /* Read the length and the chunk name.
    * This must be performed in a single I/O call.
    */
   png_read_data(png_ptr, buf, 8);
   length = png_get_uint_31(png_ptr, buf);

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

   png_debug2(0, "Reading %s chunk, length = %u",
       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);

#ifdef PNG_IO_STATE_SUPPORTED
   png_ptr->io_state = PNG_IO_READING | PNG_IO_CHUNK_DATA;
#endif

   return length;
}

/* Read data, and (optionally) run it through the CRC. */
void /* PRIVATE */
png_crc_read(png_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_benign_error(png_ptr, "CRC error");
         return (0);
      }

      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;
   }

#ifdef PNG_IO_STATE_SUPPORTED
   png_ptr->io_state = PNG_IO_READING | PNG_IO_CHUNK_CRC;
#endif

   /* The chunk CRC must be serialized in a single I/O call. */
   png_read_data(png_ptr, crc_bytes, 4);

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

   else
      return (0);
}

#ifdef PNG_READ_COMPRESSED_TEXT_SUPPORTED
static png_size_t
png_inflate(png_structp png_ptr, png_bytep data, png_size_t size,
    png_bytep output, png_size_t output_size)
{
   png_size_t count = 0;

   /* zlib can't necessarily handle more than 65535 bytes at once (i.e. it can't
    * even necessarily handle 65536 bytes) because the type uInt is "16 bits or
    * more".  Consequently it is necessary to chunk the input to zlib.  This
    * code uses ZLIB_IO_MAX, from pngpriv.h, as the maximum (the maximum value
    * that can be stored in a uInt.)  It is possible to set ZLIB_IO_MAX to a
    * lower value in pngpriv.h and this may sometimes have a performance
    * advantage, because it forces access of the input data to be separated from
    * at least some of the use by some period of time.
    */
   png_ptr->zstream.next_in = data;
   /* avail_in is set below from 'size' */
   png_ptr->zstream.avail_in = 0;

   while (1)
   {
      int ret, avail;

      /* The setting of 'avail_in' used to be outside the loop, by setting it
       * inside it is possible to chunk the input to zlib and simply rely on
       * zlib to advance the 'next_in' pointer.  This allows arbitrary amounts o
       * data to be passed through zlib at the unavoidable cost of requiring a
       * window save (memcpy of up to 32768 output bytes) every ZLIB_IO_MAX
       * input bytes.
       */
      if (png_ptr->zstream.avail_in == 0 && size > 0)
      {
         if (size <= ZLIB_IO_MAX)
         {
            /* The value is less than ZLIB_IO_MAX so the cast is safe: */
            png_ptr->zstream.avail_in = (uInt)size;
            size = 0;
         }

         else
         {
            png_ptr->zstream.avail_in = ZLIB_IO_MAX;
            size -= ZLIB_IO_MAX;
         }
      }

      /* Reset the output buffer each time round - we empty it
       * after every inflate call.
       */
      png_ptr->zstream.next_out = png_ptr->zbuf;
      png_ptr->zstream.avail_out = png_ptr->zbuf_size;

      ret = inflate(&png_ptr->zstream, Z_NO_FLUSH);
      avail = png_ptr->zbuf_size - png_ptr->zstream.avail_out;

      /* First copy/count any new output - but only if we didn't
       * get an error code.
       */
      if ((ret == Z_OK || ret == Z_STREAM_END) && avail > 0)
      {
         png_size_t space = avail; /* > 0, see above */

         if (output != 0 && output_size > count)
         {
            png_size_t copy = output_size - count;

            if (space < copy)
               copy = space;

            png_memcpy(output + count, png_ptr->zbuf, copy);
         }
         count += space;
      }

      if (ret == Z_OK)
         continue;

      /* Termination conditions - always reset the zstream, it
       * must be left in inflateInit state.
       */
      png_ptr->zstream.avail_in = 0;
      inflateReset(&png_ptr->zstream);

      if (ret == Z_STREAM_END)
         return count; /* NOTE: may be zero. */

      /* Now handle the error codes - the API always returns 0
       * and the error message is dumped into the uncompressed
       * buffer if available.
       */
      {
         PNG_CONST char *msg;
#ifdef PNG_CONSOLE_IO_SUPPORTED
         char umsg[52];
#endif
         if (png_ptr->zstream.msg != 0)
            msg = png_ptr->zstream.msg;

         else
         {
#ifdef PNG_CONSOLE_IO_SUPPORTED
            switch (ret)
            {
               case Z_BUF_ERROR:
                  msg = "Buffer error in compressed datastream in %s chunk";
                  break;

               case Z_DATA_ERROR:
                  msg = "Data error in compressed datastream in %s chunk";
                  break;

               default:
                  msg = "Incomplete compressed datastream in %s chunk";
                  break;
            }

            png_snprintf(umsg, sizeof umsg, msg, png_ptr->chunk_name);
            msg = umsg;
#else
            msg = "Damaged compressed datastream in chunk other than IDAT";
#endif
         }

         png_warning(png_ptr, msg);
      }

      /* 0 means an error - notice that this code simply ignores
       * zero length compressed chunks as a result.
       */
      return 0;
   }
}

/*
 * 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)
{
   /* The caller should guarantee this */
   if (prefix_size > chunklength)
   {
      /* The recovery is to delete the chunk. */
      png_warning(png_ptr, "invalid chunklength");
      prefix_size = 0; /* To delete everything */
   }

   else if (comp_type == PNG_COMPRESSION_TYPE_BASE)
   {
      png_size_t expanded_size = png_inflate(png_ptr,
          (png_bytep)(png_ptr->chunkdata + prefix_size),
          chunklength - prefix_size,
          0,            /*output*/
          0);           /*output size*/

      /* Now check the limits on this chunk - if the limit fails the
       * compressed data will be removed, the prefix will remain.
       */
#ifdef PNG_SET_CHUNK_MALLOC_LIMIT_SUPPORTED
      if (png_ptr->user_chunk_malloc_max &&
          (prefix_size + expanded_size >= png_ptr->user_chunk_malloc_max - 1))
#else
#  ifdef PNG_USER_CHUNK_MALLOC_MAX
      if ((PNG_USER_CHUNK_MALLOC_MAX > 0) &&
          prefix_size + expanded_size >= PNG_USER_CHUNK_MALLOC_MAX - 1)
#  endif
#endif
         png_warning(png_ptr, "Exceeded size limit while expanding chunk");

      /* If the size is zero either there was an error and a message
       * has already been output (warning) or the size really is zero
       * and we have nothing to do - the code will exit through the
       * error case below.
       */
#if defined(PNG_SET_CHUNK_MALLOC_LIMIT_SUPPORTED) || \
    defined(PNG_USER_CHUNK_MALLOC_MAX)
      else if (expanded_size > 0)
#else
      if (expanded_size > 0)
#endif
      {
         /* Success (maybe) - really uncompress the chunk. */
         png_size_t new_size = 0;
         png_charp text = png_malloc_warn(png_ptr,
             prefix_size + expanded_size + 1);

         if (text != NULL)
         {
            png_memcpy(text, png_ptr->chunkdata, prefix_size);
            new_size = png_inflate(png_ptr,
                (png_bytep)(png_ptr->chunkdata + prefix_size),
                chunklength - prefix_size,
                (png_bytep)(text + prefix_size), expanded_size);
            text[prefix_size + expanded_size] = 0; /* just in case */

            if (new_size == expanded_size)
            {
               png_free(png_ptr, png_ptr->chunkdata);
               png_ptr->chunkdata = text;
               *newlength = prefix_size + expanded_size;
               return; /* The success return! */
            }

            png_warning(png_ptr, "png_inflate logic error");
            png_free(png_ptr, text);
         }

         else
            png_warning(png_ptr, "Not enough memory to decompress chunk");
      }
   }

   else /* if (comp_type != PNG_COMPRESSION_TYPE_BASE) */
   {
#ifdef PNG_STDIO_SUPPORTED
      char umsg[50];

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

      /* The recovery is to simply drop the data. */
   }

   /* Generic error return - leave the prefix, delete the compressed
    * data, reallocate the chunkdata to remove the potentially large
    * amount of compressed data.
    */
   {
      png_charp text = png_malloc_warn(png_ptr, prefix_size + 1);

      if (text != NULL)
      {
         if (prefix_size > 0)
            png_memcpy(text, png_ptr->chunkdata, prefix_size);

         png_free(png_ptr, png_ptr->chunkdata);
         png_ptr->chunkdata = text;

         /* This is an extra zero in the 'uncompressed' part. */
         *(png_ptr->chunkdata + prefix_size) = 0x00;
      }
      /* Ignore a malloc error here - it is safe. */
   }

   *newlength = prefix_size;
}
#endif /* PNG_READ_COMPRESSED_TEXT_SUPPORTED */

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

   /* Find number of channels */
   switch (png_ptr->color_type)
   {
      default: /* invalid, png_set_IHDR calls png_error */
      case PNG_COLOR_TYPE_GRAY:
      case PNG_COLOR_TYPE_PALETTE:
         png_ptr->channels = 1;
         break;

      case PNG_COLOR_TYPE_RGB:
         png_ptr->channels = 3;
         break;

      case PNG_COLOR_TYPE_GRAY_ALPHA:
         png_ptr->channels = 2;
         break;

      case PNG_COLOR_TYPE_RGB_ALPHA:
         png_ptr->channels = 4;
         break;
   }

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

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

   png_debug(1, "in png_handle_PLTE");

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      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;
   }

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

   if (length > 3*PNG_MAX_PALETTE_LENGTH || length % 3)
   {
      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;

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

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

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

   /* If we actually need the PLTE chunk (ie for a paletted image), we do
    * whatever the normal CRC configuration tells us.  However, if we
    * have an RGB image, the PLTE can be considered ancillary, so
    * we will act as though it is.
    */
#ifndef PNG_READ_OPT_PLTE_SUPPORTED
   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
#endif
   {
      png_crc_finish(png_ptr, 0);
   }

#ifndef 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_benign_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);

#ifdef 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);

   PNG_UNUSED(info_ptr) /* Quiet compiler warnings about unused info_ptr */
}

#ifdef 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;
   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)
#ifdef 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_get_fixed_point(NULL, buf);

   /* Check for zero gamma or an error. */
   if (igamma <= 0)
   {
      png_warning(png_ptr,
          "Ignoring gAMA chunk with out of range gamma");

      return;
   }

#  ifdef 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");

#    ifdef PNG_CONSOLE_IO_SUPPORTED
         fprintf(stderr, "gamma = (%d/100000)", (int)igamma);
#    endif
         return;
      }
   }
#  endif /* PNG_READ_sRGB_SUPPORTED */

#  ifdef PNG_READ_GAMMA_SUPPORTED
   /* Gamma correction on read is supported. */
   png_ptr->gamma = igamma;
#  endif
   /* And set the 'info' structure members. */
   png_set_gAMA_fixed(png_ptr, info_ptr, igamma);
}
#endif

#ifdef 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

#ifdef 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];
   png_fixed_point x_white, y_white, x_red, y_red, x_green, y_green, x_blue,
      y_blue;

   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)
#  ifdef 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;

   x_white = png_get_fixed_point(NULL, buf);
   y_white = png_get_fixed_point(NULL, buf + 4);
   x_red   = png_get_fixed_point(NULL, buf + 8);
   y_red   = png_get_fixed_point(NULL, buf + 12);
   x_green = png_get_fixed_point(NULL, buf + 16);
   y_green = png_get_fixed_point(NULL, buf + 20);
   x_blue  = png_get_fixed_point(NULL, buf + 24);
   y_blue  = png_get_fixed_point(NULL, buf + 28);

   if (x_white == PNG_FIXED_ERROR ||
       y_white == PNG_FIXED_ERROR ||
       x_red   == PNG_FIXED_ERROR ||
       y_red   == PNG_FIXED_ERROR ||
       x_green == PNG_FIXED_ERROR ||
       y_green == PNG_FIXED_ERROR ||
       x_blue  == PNG_FIXED_ERROR ||
       y_blue  == PNG_FIXED_ERROR)
   {
      png_warning(png_ptr, "Ignoring cHRM chunk with negative chromaticities");
      return;
   }

#ifdef PNG_READ_sRGB_SUPPORTED
   if ((info_ptr != NULL) && (info_ptr->valid & PNG_INFO_sRGB))
   {
      if (PNG_OUT_OF_RANGE(x_white, 31270,  1000) ||
          PNG_OUT_OF_RANGE(y_white, 32900,  1000) ||
          PNG_OUT_OF_RANGE(x_red,   64000L, 1000) ||
          PNG_OUT_OF_RANGE(y_red,   33000,  1000) ||
          PNG_OUT_OF_RANGE(x_green, 30000,  1000) ||
          PNG_OUT_OF_RANGE(y_green, 60000L, 1000) ||
          PNG_OUT_OF_RANGE(x_blue,  15000,  1000) ||
          PNG_OUT_OF_RANGE(y_blue,   6000,  1000))
      {
         png_warning(png_ptr,
             "Ignoring incorrect cHRM value when sRGB is also present");

#ifdef PNG_CONSOLE_IO_SUPPORTED
         fprintf(stderr, "wx=%d, wy=%d, rx=%d, ry=%d\n",
             x_white, y_white, x_red, y_red);

         fprintf(stderr, "gx=%d, gy=%d, bx=%d, by=%d\n",
             x_green, y_green, x_blue, y_blue);
#endif /* PNG_CONSOLE_IO_SUPPORTED */
      }
      return;
   }
#endif /* PNG_READ_sRGB_SUPPORTED */

   png_set_cHRM_fixed(png_ptr, info_ptr, x_white, y_white, x_red, y_red,
      x_green, y_green, x_blue, y_blue);
}
#endif

#ifdef 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))
   {
      if (PNG_OUT_OF_RANGE(info_ptr->gamma, 45500L, 500))
      {
         png_warning(png_ptr,
             "Ignoring incorrect gAMA value when sRGB is also present");
#ifdef PNG_CONSOLE_IO_SUPPORTED
         fprintf(stderr, "incorrect gamma=(%d/100000)\n", info_ptr->gamma);
#endif
      }
   }
#endif /* PNG_READ_gAMA_SUPPORTED */

#ifdef PNG_READ_cHRM_SUPPORTED
   if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_cHRM))
      if (PNG_OUT_OF_RANGE(info_ptr->x_white, 31270,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->y_white, 32900,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->x_red,   64000L, 1000) ||
          PNG_OUT_OF_RANGE(info_ptr->y_red,   33000,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->x_green, 30000,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->y_green, 60000L, 1000) ||
          PNG_OUT_OF_RANGE(info_ptr->x_blue,  15000,  1000) ||
          PNG_OUT_OF_RANGE(info_ptr->y_blue,   6000,  1000))
      {
         png_warning(png_ptr,
             "Ignoring incorrect cHRM value when sRGB is also present");
      }
#endif /* PNG_READ_cHRM_SUPPORTED */

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

#ifdef 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;
   png_alloc_size_t 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))      );

   /* NOTE: the following guarantees that 'profile_length' fits into 32 bits,
    * because profile_size is a 32 bit value.
    */
   if (profile_size < profile_length)
      profile_length = profile_size;

   /* And the following guarantees that profile_size == profile_length. */
   if (profile_size > profile_length)
   {
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
#ifdef PNG_STDIO_SUPPORTED
      {
         char umsg[80];

         png_snprintf2(umsg, 80,
             "Ignoring iCCP chunk with declared size = %u "
              "and actual length = %u",
              (unsigned int) profile_size,
              (unsigned int) profile_length);
         png_warning(png_ptr, umsg);
      }
#else
      png_warning(png_ptr,
         "Ignoring iCCP chunk with uncompressed size mismatch");
#endif
      return;
   }

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

#ifdef 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;
   png_sPLT_entryp pp;
   png_uint_32 data_length;
   int entry_size, i;
   png_uint_32 skip = 0;
   png_size_t slength;
   png_uint_32 dl;
   png_size_t max_dl;

   png_debug(1, "in png_handle_sPLT");

#ifdef PNG_USER_LIMITS_SUPPORTED

   if (png_ptr->user_chunk_cache_max != 0)
   {
      if (png_ptr->user_chunk_cache_max == 1)
      {
         png_crc_finish(png_ptr, length);
         return;
      }

      if (--png_ptr->user_chunk_cache_max == 1)
      {
         png_warning(png_ptr, "No space in chunk cache for sPLT");
         png_crc_finish(png_ptr, length);
         return;
      }
   }
#endif

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      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);

   /* WARNING: this may break if size_t is less than 32 bits; it is assumed
    * that the PNG_MAX_MALLOC_64K test is enabled in this case, but this is a
    * potential breakage point if the types in pngconf.h aren't exactly right.
    */
   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);
   /* This must fit in a png_uint_32 because it is derived from the original
    * chunk data length (and use 'length', not 'slength' here for clarity -
    * they are guaranteed to be the same, see the tests above.)
    */
   data_length = length - (png_uint_32)(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;
   }

   dl = (png_int_32)(data_length / entry_size);
   max_dl = PNG_SIZE_MAX / png_sizeof(png_sPLT_entry);

   if (dl > max_dl)
   {
       png_warning(png_ptr, "sPLT chunk too long");
       return;
   }

   new_palette.nentries = (png_int_32)(data_length / entry_size);

   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;
   }

#ifdef PNG_POINTER_INDEXING_SUPPORTED
   for (i = 0; i < new_palette.nentries; i++)
   {
      pp = new_palette.entries + i;

      if (new_palette.depth == 8)
      {
         pp->red = *entry_start++;
         pp->green = *entry_start++;
         pp->blue = *entry_start++;
         pp->alpha = *entry_start++;
      }

      else
      {
         pp->red   = png_get_uint_16(entry_start); entry_start += 2;
         pp->green = png_get_uint_16(entry_start); entry_start += 2;
         pp->blue  = png_get_uint_16(entry_start); entry_start += 2;
         pp->alpha = png_get_uint_16(entry_start); entry_start += 2;
      }

      pp->frequency = png_get_uint_16(entry_start); entry_start += 2;
   }
#else
   pp = new_palette.entries;

   for (i = 0; i < new_palette.nentries; i++)
   {

      if (new_palette.depth == 8)
      {
         pp[i].red   = *entry_start++;
         pp[i].green = *entry_start++;
         pp[i].blue  = *entry_start++;
         pp[i].alpha = *entry_start++;
      }

      else
      {
         pp[i].red   = png_get_uint_16(entry_start); entry_start += 2;
         pp[i].green = png_get_uint_16(entry_start); entry_start += 2;
         pp[i].blue  = png_get_uint_16(entry_start); entry_start += 2;
         pp[i].alpha = png_get_uint_16(entry_start); entry_start += 2;
      }

      pp[i].frequency = png_get_uint_16(entry_start); entry_start += 2;
   }
#endif

   /* Discard all chunk data except the name and stash that */
   new_palette.name = png_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 */

#ifdef 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_color.gray = png_get_uint_16(buf);
   }

   else if (png_ptr->color_type == PNG_COLOR_TYPE_RGB)
   {
      png_byte buf[6];

      if (length != 6)
      {
         png_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_color.red = png_get_uint_16(buf);
      png_ptr->trans_color.green = png_get_uint_16(buf + 2);
      png_ptr->trans_color.blue = png_get_uint_16(buf + 4);
   }

   else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
   {
      if (!(png_ptr->mode & PNG_HAVE_PLTE))
      {
         /* 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_color));
}
#endif

#ifdef 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

#ifdef 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

#ifdef 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

#ifdef 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

#ifdef 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 (%u 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_size_t)(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

#ifdef 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_size_t slength, i;
   int state;

   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 (%u 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");
      png_crc_finish(png_ptr, length);
      return;
   }

   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)png_ptr->chunkdata, slength);
   png_ptr->chunkdata[slength] = 0x00; /* Null terminate the last string */

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

   /* Validate the unit. */
   if (png_ptr->chunkdata[0] != 1 && png_ptr->chunkdata[0] != 2)
   {
      png_warning(png_ptr, "Invalid sCAL ignored: invalid unit");
      png_free(png_ptr, png_ptr->chunkdata);
      png_ptr->chunkdata = NULL;
      return;
   }

   /* Validate the ASCII numbers, need two ASCII numbers separated by
    * a '\0' and they need to fit exactly in the chunk data.
    */
   i = 0;
   state = 0;

   if (png_ptr->chunkdata[1] == 45 /* negative width */ ||
       !png_check_fp_number(png_ptr->chunkdata, slength, &state, &i) ||
       i >= slength || png_ptr->chunkdata[i++] != 0)
      png_warning(png_ptr, "Invalid sCAL chunk ignored: bad width format");

   else
   {
      png_size_t heighti = i;

      if (png_ptr->chunkdata[i] == 45 /* negative height */ ||
          !png_check_fp_number(png_ptr->chunkdata, slength, &state, &i) ||
          i != slength)
         png_warning(png_ptr, "Invalid sCAL chunk ignored: bad height format");

      else
         /* This is the (only) success case. */
         png_set_sCAL_s(png_ptr, info_ptr, png_ptr->chunkdata[0],
            png_ptr->chunkdata+1, png_ptr->chunkdata+heighti);
   }

   /* Clean up - just free the temporarily allocated buffer. */
   png_free(png_ptr, png_ptr->chunkdata);
   png_ptr->chunkdata = NULL;
}
#endif

#ifdef 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

#ifdef 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");

#ifdef PNG_USER_LIMITS_SUPPORTED
   if (png_ptr->user_chunk_cache_max != 0)
   {
      if (png_ptr->user_chunk_cache_max == 1)
      {
         png_crc_finish(png_ptr, length);
         return;
      }

      if (--png_ptr->user_chunk_cache_max == 1)
      {
         png_warning(png_ptr, "No space in chunk cache for tEXt");
         png_crc_finish(png_ptr, length);
         return;
      }
   }
#endif

   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_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;
   text_ptr->lang = NULL;
   text_ptr->lang_key = NULL;
   text_ptr->itxt_length = 0;
   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

#ifdef 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");

#ifdef PNG_USER_LIMITS_SUPPORTED
   if (png_ptr->user_chunk_cache_max != 0)
   {
      if (png_ptr->user_chunk_cache_max == 1)
      {
         png_crc_finish(png_ptr, length);
         return;
      }

      if (--png_ptr->user_chunk_cache_max == 1)
      {
         png_warning(png_ptr, "No space in chunk cache for zTXt");
         png_crc_finish(png_ptr, length);
         return;
      }
   }
#endif

   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_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;
   text_ptr->lang = NULL;
   text_ptr->lang_key = NULL;
   text_ptr->itxt_length = 0;
   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

#ifdef 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");

#ifdef PNG_USER_LIMITS_SUPPORTED
   if (png_ptr->user_chunk_cache_max != 0)
   {
      if (png_ptr->user_chunk_cache_max == 1)
      {
         png_crc_finish(png_ptr, length);
         return;
      }

      if (--png_ptr->user_chunk_cache_max == 1)
      {
         png_warning(png_ptr, "No space in chunk cache for iTXt");
         png_crc_finish(png_ptr, length);
         return;
      }
   }
#endif

   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_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");

#ifdef PNG_USER_LIMITS_SUPPORTED
   if (png_ptr->user_chunk_cache_max != 0)
   {
      if (png_ptr->user_chunk_cache_max == 1)
      {
         png_crc_finish(png_ptr, length);
         return;
      }

      if (--png_ptr->user_chunk_cache_max == 1)
      {
         png_warning(png_ptr, "No space in chunk cache for unknown chunk");
         png_crc_finish(png_ptr, length);
         return;
      }
   }
#endif

   if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      PNG_IDAT;

      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))
   {
#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
      if (png_handle_as_unknown(png_ptr, png_ptr->chunk_name) !=
          PNG_HANDLE_CHUNK_ALWAYS
#ifdef PNG_READ_USER_CHUNKS_SUPPORTED
          && png_ptr->read_user_chunk_fn == NULL
#endif
          )
#endif
         png_chunk_error(png_ptr, "unknown critical chunk");
   }

#ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
   if ((png_ptr->flags & PNG_FLAG_KEEP_UNKNOWN_CHUNKS)
#ifdef PNG_READ_USER_CHUNKS_SUPPORTED
       || (png_ptr->read_user_chunk_fn != NULL)
#endif
       )
   {
#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);
      }

#ifdef 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))
            {
#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
               if (png_handle_as_unknown(png_ptr, png_ptr->chunk_name) !=
                   PNG_HANDLE_CHUNK_ALWAYS)
#endif
                  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);

#ifndef PNG_READ_USER_CHUNKS_SUPPORTED
   PNG_UNUSED(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_const_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;

#ifdef 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;

#ifdef 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;

#ifdef 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
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;
   /* 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};

   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;

#ifdef 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;

#ifdef 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];

#ifdef 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);
   }
#ifndef PNG_READ_PACKSWAP_SUPPORTED
   PNG_UNUSED(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_const_bytep prev_row, int filter)
{
   png_debug(1, "in png_read_filter_row");
   png_debug2(2, "row = %u, filter = %d", png_ptr->row_number, filter);
   switch (filter)
   {
      case PNG_FILTER_VALUE_NONE:
         break;

      case PNG_FILTER_VALUE_SUB:
      {
         png_size_t i;
         png_size_t istop = row_info->rowbytes;
         unsigned int 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_size_t i;
         png_size_t istop = row_info->rowbytes;
         png_bytep rp = row;
         png_const_bytep pp = prev_row;

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

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

            rp++;
         }

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

            rp++;
         }
         break;
      }
      case PNG_FILTER_VALUE_PAETH:
      {
         png_size_t i;
         png_bytep rp = row;
         png_const_bytep pp = prev_row;
         png_bytep lp = row;
         png_const_bytep cp = prev_row;
         unsigned int bpp = (row_info->pixel_depth + 7) >> 3;
         png_size_t 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_error(png_ptr, "Ignoring bad adaptive filter type");
         /*NOT REACHED */
         break;
   }
}

#ifdef PNG_SEQUENTIAL_READ_SUPPORTED
void /* PRIVATE */
png_read_finish_row(png_structp png_ptr)
{
#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 */

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

      do
      {
         png_ptr->pass++;

         if (png_ptr->pass >= 7)
            break;

         png_ptr->iwidth = (png_ptr->width +
            png_pass_inc[png_ptr->pass] - 1 -
            png_pass_start[png_ptr->pass]) /
            png_pass_inc[png_ptr->pass];

         if (!(png_ptr->transformations & PNG_INTERLACE))
         {
            png_ptr->num_rows = (png_ptr->height +
                png_pass_yinc[png_ptr->pass] - 1 -
                png_pass_ystart[png_ptr->pass]) /
                png_pass_yinc[png_ptr->pass];
         }

         else  /* if (png_ptr->transformations & PNG_INTERLACE) */
            break; /* libpng deinterlacing sees every row */

      } while (png_ptr->num_rows == 0 || png_ptr->iwidth == 0);

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

   if (!(png_ptr->flags & PNG_FLAG_ZLIB_FINISHED))
   {
      PNG_IDAT;
      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_crc_finish(png_ptr, 0);
               png_ptr->idat_size = png_read_chunk_header(png_ptr);
               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;
}
#endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

void /* PRIVATE */
png_read_start_row(png_structp png_ptr)
{
#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

   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];
   }

   else
#endif /* PNG_READ_INTERLACING_SUPPORTED */
   {
      png_ptr->num_rows = png_ptr->height;
      png_ptr->iwidth = png_ptr->width;
   }

   max_pixel_depth = png_ptr->pixel_depth;

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

#ifdef 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

#ifdef PNG_READ_EXPAND_16_SUPPORTED
   if (png_ptr->transformations & PNG_EXPAND_16)
   {
#     ifdef PNG_READ_EXPAND_SUPPORTED
         /* In fact it is an error if it isn't supported, but checking is
          * the safe way.
          */
         if (png_ptr->transformations & PNG_EXPAND)
         {
            if (png_ptr->bit_depth < 16)
               max_pixel_depth *= 2;
         }
         else
#     endif
         png_ptr->transformations &= ~PNG_EXPAND_16;
   }
#endif

#ifdef PNG_READ_FILLER_SUPPORTED
   if (png_ptr->transformations & (PNG_FILLER))
   {
      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

#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
   if (png_ptr->transformations & PNG_GRAY_TO_RGB)
   {
      if (
#ifdef PNG_READ_EXPAND_SUPPORTED
          (png_ptr->num_trans && (png_ptr->transformations & PNG_EXPAND)) ||
#endif
#ifdef 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 + 48 > png_ptr->old_big_row_buf_size)
   {
     png_free(png_ptr, png_ptr->big_row_buf);

     if (png_ptr->interlaced)
        png_ptr->big_row_buf = (png_bytep)png_calloc(png_ptr,
            row_bytes + 48);

     else
        png_ptr->big_row_buf = (png_bytep)png_malloc(png_ptr,
            row_bytes + 48);

     png_ptr->old_big_row_buf_size = row_bytes + 48;

#ifdef PNG_ALIGNED_MEMORY_SUPPORTED
     /* Use 16-byte aligned memory for row_buf with at least 16 bytes
      * of padding before and after row_buf.
      */
     png_ptr->row_buf = png_ptr->big_row_buf + 32 -
         (((png_alloc_size_t)png_ptr->big_row_buf + 15) & 0x0F);

     png_ptr->old_big_row_buf_size = row_bytes + 48;
#else
     /* Use 32 bytes of padding before and 16 bytes after row_buf. */
     png_ptr->row_buf = png_ptr->big_row_buf + 32;
#endif
     png_ptr->old_big_row_buf_size = row_bytes + 48;
   }

#ifdef PNG_MAX_MALLOC_64K
   if (png_ptr->rowbytes > 65535)
      png_error(png_ptr, "This image requires a row greater than 64KB");

#endif
   if (png_ptr->rowbytes > (PNG_SIZE_MAX - 1))
      png_error(png_ptr, "Row has too many bytes to allocate in memory");

   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_ptr->rowbytes + 1);

      png_ptr->old_prev_row_size = png_ptr->rowbytes + 1;
   }

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

   png_debug1(3, "width = %u,", png_ptr->width);
   png_debug1(3, "height = %u,", png_ptr->height);
   png_debug1(3, "iwidth = %u,", png_ptr->iwidth);
   png_debug1(3, "num_rows = %u,", png_ptr->num_rows);
   png_debug1(3, "rowbytes = %lu,", (unsigned long)png_ptr->rowbytes);
   png_debug1(3, "irowbytes = %lu",
       (unsigned long)PNG_ROWBYTES(png_ptr->pixel_depth, png_ptr->iwidth) + 1);

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