
/* pngpread.c - read a png file in push mode
 *
 * Last changed in libpng 1.4.10 [March 8, 2012]
 * Copyright (c) 1998-2012 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
 */

#define PNG_NO_PEDANTIC_WARNINGS
#include "png.h"
#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
#include "pngpriv.h"

/* Push model modes */
#define PNG_READ_SIG_MODE   0
#define PNG_READ_CHUNK_MODE 1
#define PNG_READ_IDAT_MODE  2
#define PNG_SKIP_MODE       3
#define PNG_READ_tEXt_MODE  4
#define PNG_READ_zTXt_MODE  5
#define PNG_READ_DONE_MODE  6
#define PNG_READ_iTXt_MODE  7
#define PNG_ERROR_MODE      8

void PNGAPI
png_process_data(png_structp png_ptr, png_infop info_ptr,
   png_bytep buffer, png_size_t buffer_size)
{
   if (png_ptr == NULL || info_ptr == NULL)
      return;

   png_push_restore_buffer(png_ptr, buffer, buffer_size);

   while (png_ptr->buffer_size)
   {
      png_process_some_data(png_ptr, info_ptr);
   }
}

/* What we do with the incoming data depends on what we were previously
 * doing before we ran out of data...
 */
void /* PRIVATE */
png_process_some_data(png_structp png_ptr, png_infop info_ptr)
{
   if (png_ptr == NULL)
      return;

   switch (png_ptr->process_mode)
   {
      case PNG_READ_SIG_MODE:
      {
         png_push_read_sig(png_ptr, info_ptr);
         break;
      }

      case PNG_READ_CHUNK_MODE:
      {
         png_push_read_chunk(png_ptr, info_ptr);
         break;
      }

      case PNG_READ_IDAT_MODE:
      {
         png_push_read_IDAT(png_ptr);
         break;
      }

      case PNG_SKIP_MODE:
      {
         png_push_crc_finish(png_ptr);
         break;
      }

      default:
      {
         png_ptr->buffer_size = 0;
         break;
      }
   }
}

/* Read any remaining signature bytes from the stream and compare them with
 * the correct PNG signature.  It is possible that this routine is called
 * with bytes already read from the signature, either because they have been
 * checked by the calling application, or because of multiple calls to this
 * routine.
 */
void /* PRIVATE */
png_push_read_sig(png_structp png_ptr, png_infop info_ptr)
{
   png_size_t num_checked = png_ptr->sig_bytes,
             num_to_check = 8 - num_checked;

   if (png_ptr->buffer_size < num_to_check)
   {
      num_to_check = png_ptr->buffer_size;
   }

   png_push_fill_buffer(png_ptr, &(info_ptr->signature[num_checked]),
      num_to_check);
   png_ptr->sig_bytes = (png_byte)(png_ptr->sig_bytes + num_to_check);

   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");
   }
   else
   {
      if (png_ptr->sig_bytes >= 8)
      {
         png_ptr->process_mode = PNG_READ_CHUNK_MODE;
      }
   }
}

void /* PRIVATE */
png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
{
      PNG_IHDR;
      PNG_IDAT;
      PNG_IEND;
      PNG_PLTE;
#ifdef PNG_READ_bKGD_SUPPORTED
      PNG_bKGD;
#endif
#ifdef PNG_READ_cHRM_SUPPORTED
      PNG_cHRM;
#endif
#ifdef PNG_READ_gAMA_SUPPORTED
      PNG_gAMA;
#endif
#ifdef PNG_READ_hIST_SUPPORTED
      PNG_hIST;
#endif
#ifdef PNG_READ_iCCP_SUPPORTED
      PNG_iCCP;
#endif
#ifdef PNG_READ_iTXt_SUPPORTED
      PNG_iTXt;
#endif
#ifdef PNG_READ_oFFs_SUPPORTED
      PNG_oFFs;
#endif
#ifdef PNG_READ_pCAL_SUPPORTED
      PNG_pCAL;
#endif
#ifdef PNG_READ_pHYs_SUPPORTED
      PNG_pHYs;
#endif
#ifdef PNG_READ_sBIT_SUPPORTED
      PNG_sBIT;
#endif
#ifdef PNG_READ_sCAL_SUPPORTED
      PNG_sCAL;
#endif
#ifdef PNG_READ_sRGB_SUPPORTED
      PNG_sRGB;
#endif
#ifdef PNG_READ_sPLT_SUPPORTED
      PNG_sPLT;
#endif
#ifdef PNG_READ_tEXt_SUPPORTED
      PNG_tEXt;
#endif
#ifdef PNG_READ_tIME_SUPPORTED
      PNG_tIME;
#endif
#ifdef PNG_READ_tRNS_SUPPORTED
      PNG_tRNS;
#endif
#ifdef PNG_READ_zTXt_SUPPORTED
      PNG_zTXt;
#endif

   /* First we make sure we have enough data for the 4 byte chunk name
    * and the 4 byte chunk length before proceeding with decoding the
    * chunk data.  To fully decode each of these chunks, we also make
    * sure we have enough data in the buffer for the 4 byte CRC at the
    * end of every chunk (except IDAT, which is handled separately).
    */
   if (!(png_ptr->mode & PNG_HAVE_CHUNK_HEADER))
   {
      png_byte chunk_length[4];

      if (png_ptr->buffer_size < 8)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_push_fill_buffer(png_ptr, chunk_length, 4);
      png_ptr->push_length = png_get_uint_31(png_ptr, chunk_length);
      png_reset_crc(png_ptr);
      png_crc_read(png_ptr, png_ptr->chunk_name, 4);
      png_check_chunk_name(png_ptr, png_ptr->chunk_name);
      png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;
   }

   if (!png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
     if (png_ptr->mode & PNG_AFTER_IDAT)
        png_ptr->mode |= PNG_HAVE_CHUNK_AFTER_IDAT;

   if (!png_memcmp(png_ptr->chunk_name, png_IHDR, 4))
   {
      if (png_ptr->push_length != 13)
         png_error(png_ptr, "Invalid IHDR length");

      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_IHDR(png_ptr, info_ptr, png_ptr->push_length);
   }

   else if (!png_memcmp(png_ptr->chunk_name, png_IEND, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_IEND(png_ptr, info_ptr, png_ptr->push_length);

      png_ptr->process_mode = PNG_READ_DONE_MODE;
      png_push_have_end(png_ptr, info_ptr);
   }

#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
   else if (png_handle_as_unknown(png_ptr, png_ptr->chunk_name))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      if (!png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
         png_ptr->mode |= PNG_HAVE_IDAT;

      png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length);

      if (!png_memcmp(png_ptr->chunk_name, png_PLTE, 4))
         png_ptr->mode |= PNG_HAVE_PLTE;

      else if (!png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
      {
         if (!(png_ptr->mode & PNG_HAVE_IHDR))
            png_error(png_ptr, "Missing IHDR before IDAT");

         else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
                  !(png_ptr->mode & PNG_HAVE_PLTE))
            png_error(png_ptr, "Missing PLTE before IDAT");
      }
   }

#endif
   else if (!png_memcmp(png_ptr->chunk_name, png_PLTE, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }
      png_handle_PLTE(png_ptr, info_ptr, png_ptr->push_length);
   }

   else if (!png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
   {
      /* If we reach an IDAT chunk, this means we have read all of the
       * header chunks, and we can start reading the image (or if this
       * is called after the image has been read - we have an error).
       */

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

      else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
          !(png_ptr->mode & PNG_HAVE_PLTE))
         png_error(png_ptr, "Missing PLTE before IDAT");

      if (png_ptr->mode & PNG_HAVE_IDAT)
      {
         if (!(png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))
            if (png_ptr->push_length == 0)
               return;

         if (png_ptr->mode & PNG_AFTER_IDAT)
            png_benign_error(png_ptr, "Too many IDATs found");
      }

      png_ptr->idat_size = png_ptr->push_length;
      png_ptr->mode |= PNG_HAVE_IDAT;
      png_ptr->process_mode = PNG_READ_IDAT_MODE;
      png_push_have_info(png_ptr, info_ptr);
      png_ptr->zstream.avail_out =
          (uInt) PNG_ROWBYTES(png_ptr->pixel_depth,
          png_ptr->iwidth) + 1;
      png_ptr->zstream.next_out = png_ptr->row_buf;
      return;
   }

#ifdef PNG_READ_gAMA_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_gAMA, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_gAMA(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_sBIT_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_sBIT, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_sBIT(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_cHRM_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_cHRM, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_cHRM(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_sRGB_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_sRGB, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_sRGB(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_iCCP_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_iCCP, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_iCCP(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_sPLT_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_sPLT, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_sPLT(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_tRNS_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_tRNS, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_tRNS(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_bKGD_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_bKGD, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_bKGD(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_hIST_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_hIST, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_hIST(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_pHYs_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_pHYs, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_pHYs(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_oFFs_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_oFFs, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_oFFs(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif

#ifdef PNG_READ_pCAL_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_pCAL, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_pCAL(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_sCAL_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_sCAL, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_sCAL(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_tIME_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_tIME, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_tIME(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_tEXt_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_tEXt, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_tEXt(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_zTXt_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_zTXt, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_zTXt(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
#ifdef PNG_READ_iTXt_SUPPORTED
   else if (!png_memcmp(png_ptr->chunk_name, png_iTXt, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_iTXt(png_ptr, info_ptr, png_ptr->push_length);
   }

#endif
   else
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }
      png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length);
   }

   png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
}

void /* PRIVATE */
png_push_crc_skip(png_structp png_ptr, png_uint_32 skip)
{
   png_ptr->process_mode = PNG_SKIP_MODE;
   png_ptr->skip_length = skip;
}

void /* PRIVATE */
png_push_crc_finish(png_structp png_ptr)
{
   if (png_ptr->skip_length && png_ptr->save_buffer_size)
   {
      png_size_t save_size;

      if (png_ptr->skip_length < (png_uint_32)png_ptr->save_buffer_size)
         save_size = (png_size_t)png_ptr->skip_length;
      else
         save_size = png_ptr->save_buffer_size;

      png_calculate_crc(png_ptr, png_ptr->save_buffer_ptr, save_size);

      png_ptr->skip_length -= save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->save_buffer_size -= save_size;
      png_ptr->save_buffer_ptr += save_size;
   }
   if (png_ptr->skip_length && png_ptr->current_buffer_size)
   {
      png_size_t save_size;

      if (png_ptr->skip_length < (png_uint_32)png_ptr->current_buffer_size)
         save_size = (png_size_t)png_ptr->skip_length;
      else
         save_size = png_ptr->current_buffer_size;

      png_calculate_crc(png_ptr, png_ptr->current_buffer_ptr, save_size);

      png_ptr->skip_length -= save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->current_buffer_size -= save_size;
      png_ptr->current_buffer_ptr += save_size;
   }
   if (!png_ptr->skip_length)
   {
      if (png_ptr->buffer_size < 4)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_crc_finish(png_ptr, 0);
      png_ptr->process_mode = PNG_READ_CHUNK_MODE;
   }
}

void PNGAPI
png_push_fill_buffer(png_structp png_ptr, png_bytep buffer, png_size_t length)
{
   png_bytep ptr;

   if (png_ptr == NULL)
      return;

   ptr = buffer;
   if (png_ptr->save_buffer_size)
   {
      png_size_t save_size;

      if (length < png_ptr->save_buffer_size)
         save_size = length;
      else
         save_size = png_ptr->save_buffer_size;

      png_memcpy(ptr, png_ptr->save_buffer_ptr, save_size);
      length -= save_size;
      ptr += save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->save_buffer_size -= save_size;
      png_ptr->save_buffer_ptr += save_size;
   }
   if (length && png_ptr->current_buffer_size)
   {
      png_size_t save_size;

      if (length < png_ptr->current_buffer_size)
         save_size = length;

      else
         save_size = png_ptr->current_buffer_size;

      png_memcpy(ptr, png_ptr->current_buffer_ptr, save_size);
      png_ptr->buffer_size -= save_size;
      png_ptr->current_buffer_size -= save_size;
      png_ptr->current_buffer_ptr += save_size;
   }
}

void /* PRIVATE */
png_push_save_buffer(png_structp png_ptr)
{
   if (png_ptr->save_buffer_size)
   {
      if (png_ptr->save_buffer_ptr != png_ptr->save_buffer)
      {
         png_size_t i, istop;
         png_bytep sp;
         png_bytep dp;

         istop = png_ptr->save_buffer_size;
         for (i = 0, sp = png_ptr->save_buffer_ptr, dp = png_ptr->save_buffer;
            i < istop; i++, sp++, dp++)
         {
            *dp = *sp;
         }
      }
   }
   if (png_ptr->save_buffer_size + png_ptr->current_buffer_size >
      png_ptr->save_buffer_max)
   {
      png_size_t new_max;
      png_bytep old_buffer;

      if (png_ptr->save_buffer_size > PNG_SIZE_MAX -
         (png_ptr->current_buffer_size + 256))
      {
        png_error(png_ptr, "Potential overflow of save_buffer");
      }

      new_max = png_ptr->save_buffer_size + png_ptr->current_buffer_size + 256;
      old_buffer = png_ptr->save_buffer;
      png_ptr->save_buffer = (png_bytep)png_malloc_warn(png_ptr,
         new_max);
      if (png_ptr->save_buffer == NULL)
      {
        png_free(png_ptr, old_buffer);
        png_error(png_ptr, "Insufficient memory for save_buffer");
      }
      png_memcpy(png_ptr->save_buffer, old_buffer, png_ptr->save_buffer_size);
      png_free(png_ptr, old_buffer);
      png_ptr->save_buffer_max = new_max;
   }
   if (png_ptr->current_buffer_size)
   {
      png_memcpy(png_ptr->save_buffer + png_ptr->save_buffer_size,
         png_ptr->current_buffer_ptr, png_ptr->current_buffer_size);
      png_ptr->save_buffer_size += png_ptr->current_buffer_size;
      png_ptr->current_buffer_size = 0;
   }
   png_ptr->save_buffer_ptr = png_ptr->save_buffer;
   png_ptr->buffer_size = 0;
}

void /* PRIVATE */
png_push_restore_buffer(png_structp png_ptr, png_bytep buffer,
   png_size_t buffer_length)
{
   png_ptr->current_buffer = buffer;
   png_ptr->current_buffer_size = buffer_length;
   png_ptr->buffer_size = buffer_length + png_ptr->save_buffer_size;
   png_ptr->current_buffer_ptr = png_ptr->current_buffer;
}

void /* PRIVATE */
png_push_read_IDAT(png_structp png_ptr)
{
   PNG_IDAT;
   if (!(png_ptr->mode & PNG_HAVE_CHUNK_HEADER))
   {
      png_byte chunk_length[4];

      if (png_ptr->buffer_size < 8)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_push_fill_buffer(png_ptr, chunk_length, 4);
      png_ptr->push_length = png_get_uint_31(png_ptr, chunk_length);
      png_reset_crc(png_ptr);
      png_crc_read(png_ptr, png_ptr->chunk_name, 4);
      png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;

      if (png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
      {
         png_ptr->process_mode = PNG_READ_CHUNK_MODE;
         if (!(png_ptr->flags & PNG_FLAG_ZLIB_FINISHED))
            png_error(png_ptr, "Not enough compressed data");
         return;
      }

      png_ptr->idat_size = png_ptr->push_length;
   }
   if (png_ptr->idat_size && png_ptr->save_buffer_size)
   {
      png_size_t save_size;

      if (png_ptr->idat_size < (png_uint_32)png_ptr->save_buffer_size)
      {
         save_size = (png_size_t)png_ptr->idat_size;

         /* Check for overflow */
         if ((png_uint_32)save_size != png_ptr->idat_size)
            png_error(png_ptr, "save_size overflowed in pngpread");
      }
      else
         save_size = png_ptr->save_buffer_size;

      png_calculate_crc(png_ptr, png_ptr->save_buffer_ptr, save_size);

      png_process_IDAT_data(png_ptr, png_ptr->save_buffer_ptr, save_size);

      png_ptr->idat_size -= save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->save_buffer_size -= save_size;
      png_ptr->save_buffer_ptr += save_size;
   }
   if (png_ptr->idat_size && png_ptr->current_buffer_size)
   {
      png_size_t save_size;

      if (png_ptr->idat_size < (png_uint_32)png_ptr->current_buffer_size)
      {
         save_size = (png_size_t)png_ptr->idat_size;

         /* Check for overflow */
         if ((png_uint_32)save_size != png_ptr->idat_size)
            png_error(png_ptr, "save_size overflowed in pngpread");
      }
      else
         save_size = png_ptr->current_buffer_size;

      png_calculate_crc(png_ptr, png_ptr->current_buffer_ptr, save_size);

      png_process_IDAT_data(png_ptr, png_ptr->current_buffer_ptr, save_size);

      png_ptr->idat_size -= save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->current_buffer_size -= save_size;
      png_ptr->current_buffer_ptr += save_size;
   }
   if (!png_ptr->idat_size)
   {
      if (png_ptr->buffer_size < 4)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_crc_finish(png_ptr, 0);
      png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
      png_ptr->mode |= PNG_AFTER_IDAT;
   }
}

void /* PRIVATE */
png_process_IDAT_data(png_structp png_ptr, png_bytep buffer,
   png_size_t buffer_length)
{
   /* The caller checks for a non-zero buffer length. */
   if (!(buffer_length > 0) || buffer == NULL)
      png_error(png_ptr, "No IDAT data (internal error)");

   /* This routine must process all the data it has been given
    * before returning, calling the row callback as required to
    * handle the uncompressed results.
    */
   png_ptr->zstream.next_in = buffer;
   png_ptr->zstream.avail_in = (uInt)buffer_length;

   /* Keep going until the decompressed data is all processed
    * or the stream marked as finished.
    */
   while (png_ptr->zstream.avail_in > 0 &&
      !(png_ptr->flags & PNG_FLAG_ZLIB_FINISHED))
   {
      int ret;

      /* We have data for zlib, but we must check that zlib
       * has somewhere to put the results.  It doesn't matter
       * if we don't expect any results -- it may be the input
       * data is just the LZ end code.
       */
      if (!(png_ptr->zstream.avail_out > 0))
      {
         png_ptr->zstream.avail_out =
             (uInt) PNG_ROWBYTES(png_ptr->pixel_depth,
             png_ptr->iwidth) + 1;
         png_ptr->zstream.next_out = png_ptr->row_buf;
      }

      /* Using Z_SYNC_FLUSH here means that an unterminated
       * LZ stream can still be handled (a stream with a missing
       * end code), otherwise (Z_NO_FLUSH) a future zlib
       * implementation might defer output and, therefore,
       * change the current behavior.  (See comments in inflate.c
       * for why this doesn't happen at present with zlib 1.2.5.)
       */
      ret = inflate(&png_ptr->zstream, Z_SYNC_FLUSH);

      /* Check for any failure before proceeding. */
      if (ret != Z_OK && ret != Z_STREAM_END)
      {
         /* Terminate the decompression. */
         png_ptr->flags |= PNG_FLAG_ZLIB_FINISHED;

         /* This may be a truncated stream (missing or
          * damaged end code).  Treat that as a warning.
          */
         if (png_ptr->row_number >= png_ptr->num_rows ||
             png_ptr->pass > 6)
            png_warning(png_ptr, "Truncated compressed data in IDAT");
         else
            png_error(png_ptr, "Decompression error in IDAT");

         /* Skip the check on unprocessed input */
         return;
      }

      /* Did inflate output any data? */
      if (png_ptr->zstream.next_out != png_ptr->row_buf)
      {
         /* Is this unexpected data after the last row?
          * If it is, artificially terminate the LZ output
          * here.
          */
         if (png_ptr->row_number >= png_ptr->num_rows ||
             png_ptr->pass > 6)
         {
            /* Extra data. */
            png_warning(png_ptr, "Extra compressed data in IDAT");
            png_ptr->flags |= PNG_FLAG_ZLIB_FINISHED;
            /* Do no more processing; skip the unprocessed
             * input check below.
             */
            return;
         }

         /* Do we have a complete row? */
         if (png_ptr->zstream.avail_out == 0)
            png_push_process_row(png_ptr);
      }

      /* And check for the end of the stream. */
      if (ret == Z_STREAM_END)
         png_ptr->flags |= PNG_FLAG_ZLIB_FINISHED;
   }

   /* All the data should have been processed, if anything
    * is left at this point we have bytes of IDAT data
    * after the zlib end code.
    */
   if (png_ptr->zstream.avail_in > 0)
      png_warning(png_ptr, "Extra compression data");
}

void /* PRIVATE */
png_push_process_row(png_structp png_ptr)
{
   png_ptr->row_info.color_type = png_ptr->color_type;
   png_ptr->row_info.width = png_ptr->iwidth;
   png_ptr->row_info.channels = png_ptr->channels;
   png_ptr->row_info.bit_depth = png_ptr->bit_depth;
   png_ptr->row_info.pixel_depth = png_ptr->pixel_depth;

   png_ptr->row_info.rowbytes = PNG_ROWBYTES(png_ptr->row_info.pixel_depth,
       png_ptr->row_info.width);

   png_read_filter_row(png_ptr, &(png_ptr->row_info),
       png_ptr->row_buf + 1, png_ptr->prev_row + 1,
       (int)(png_ptr->row_buf[0]));

   png_memcpy(png_ptr->prev_row, png_ptr->row_buf, png_ptr->rowbytes + 1);

   if (png_ptr->transformations || (png_ptr->flags&PNG_FLAG_STRIP_ALPHA))
      png_do_read_transformations(png_ptr);

#ifdef PNG_READ_INTERLACING_SUPPORTED
   /* Blow up interlaced rows to full size */
   if (png_ptr->interlaced && (png_ptr->transformations & PNG_INTERLACE))
   {
      if (png_ptr->pass < 6)
/*       old interface (pre-1.0.9):
         png_do_read_interlace(&(png_ptr->row_info),
             png_ptr->row_buf + 1, png_ptr->pass, png_ptr->transformations);
 */
         png_do_read_interlace(png_ptr);

    switch (png_ptr->pass)
    {
         case 0:
         {
            int i;
            for (i = 0; i < 8 && png_ptr->pass == 0; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr); /* Updates png_ptr->pass */
            }

            if (png_ptr->pass == 2) /* Pass 1 might be empty */
            {
               for (i = 0; i < 4 && png_ptr->pass == 2; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            if (png_ptr->pass == 4 && png_ptr->height <= 4)
            {
               for (i = 0; i < 2 && png_ptr->pass == 4; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            if (png_ptr->pass == 6 && png_ptr->height <= 4)
            {
                png_push_have_row(png_ptr, NULL);
                png_read_push_finish_row(png_ptr);
            }

            break;
         }

         case 1:
         {
            int i;
            for (i = 0; i < 8 && png_ptr->pass == 1; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 2) /* Skip top 4 generated rows */
            {
               for (i = 0; i < 4 && png_ptr->pass == 2; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            break;
         }

         case 2:
         {
            int i;

            for (i = 0; i < 4 && png_ptr->pass == 2; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            for (i = 0; i < 4 && png_ptr->pass == 2; i++)
            {
               png_push_have_row(png_ptr, NULL);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 4) /* Pass 3 might be empty */
            {
               for (i = 0; i < 2 && png_ptr->pass == 4; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            break;
         }

         case 3:
         {
            int i;

            for (i = 0; i < 4 && png_ptr->pass == 3; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 4) /* Skip top two generated rows */
            {
               for (i = 0; i < 2 && png_ptr->pass == 4; i++)
               {
                  png_push_have_row(png_ptr, NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }

            break;
         }

         case 4:
         {
            int i;

            for (i = 0; i < 2 && png_ptr->pass == 4; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            for (i = 0; i < 2 && png_ptr->pass == 4; i++)
            {
               png_push_have_row(png_ptr, NULL);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 6) /* Pass 5 might be empty */
            {
               png_push_have_row(png_ptr, NULL);
               png_read_push_finish_row(png_ptr);
            }

            break;
         }

         case 5:
         {
            int i;

            for (i = 0; i < 2 && png_ptr->pass == 5; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }

            if (png_ptr->pass == 6) /* Skip top generated row */
            {
               png_push_have_row(png_ptr, NULL);
               png_read_push_finish_row(png_ptr);
            }

            break;
         }

         default:
         case 6:
         {
            png_push_have_row(png_ptr, png_ptr->row_buf + 1);
            png_read_push_finish_row(png_ptr);

            if (png_ptr->pass != 6)
               break;

            png_push_have_row(png_ptr, NULL);
            png_read_push_finish_row(png_ptr);
         }
      }
   }
   else
#endif
   {
      png_push_have_row(png_ptr, png_ptr->row_buf + 1);
      png_read_push_finish_row(png_ptr);
   }
}

void /* PRIVATE */
png_read_push_finish_row(png_structp png_ptr)
{
   /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */

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

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

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

   /* Offset to next interlace block in the y direction */
   PNG_CONST int FARDATA png_pass_yinc[] = {8, 8, 8, 4, 4, 2, 2};

   /* Height of interlace block.  This is not currently used - if you need
    * it, uncomment it here and in png.h
   PNG_CONST int FARDATA png_pass_height[] = {8, 8, 4, 4, 2, 2, 1};
   */

   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 == 1 && png_ptr->width < 5) ||
             (png_ptr->pass == 3 && png_ptr->width < 3) ||
             (png_ptr->pass == 5 && png_ptr->width < 2))
           png_ptr->pass++;

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

         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];

      } while (png_ptr->iwidth == 0 || png_ptr->num_rows == 0);
   }
#endif /* PNG_READ_INTERLACING_SUPPORTED */
}

void /* PRIVATE */
png_push_have_info(png_structp png_ptr, png_infop info_ptr)
{
   if (png_ptr->info_fn != NULL)
      (*(png_ptr->info_fn))(png_ptr, info_ptr);
}

void /* PRIVATE */
png_push_have_end(png_structp png_ptr, png_infop info_ptr)
{
   if (png_ptr->end_fn != NULL)
      (*(png_ptr->end_fn))(png_ptr, info_ptr);
}

void /* PRIVATE */
png_push_have_row(png_structp png_ptr, png_bytep row)
{
   if (png_ptr->row_fn != NULL)
      (*(png_ptr->row_fn))(png_ptr, row, png_ptr->row_number,
         (int)png_ptr->pass);
}

void PNGAPI
png_progressive_combine_row(png_structp png_ptr,
   png_bytep old_row, png_bytep new_row)
{
   PNG_CONST int FARDATA png_pass_dsp_mask[7] =
      {0xff, 0x0f, 0xff, 0x33, 0xff, 0x55, 0xff};

   if (png_ptr == NULL)
      return;

   if (new_row != NULL)    /* new_row must == png_ptr->row_buf here. */
      png_combine_row(png_ptr, old_row, png_pass_dsp_mask[png_ptr->pass]);
}

void PNGAPI
png_set_progressive_read_fn(png_structp png_ptr, png_voidp progressive_ptr,
   png_progressive_info_ptr info_fn, png_progressive_row_ptr row_fn,
   png_progressive_end_ptr end_fn)
{
   if (png_ptr == NULL)
      return;

   png_ptr->info_fn = info_fn;
   png_ptr->row_fn = row_fn;
   png_ptr->end_fn = end_fn;

   png_set_read_fn(png_ptr, progressive_ptr, png_push_fill_buffer);
}

png_voidp PNGAPI
png_get_progressive_ptr(png_const_structp png_ptr)
{
   if (png_ptr == NULL)
      return (NULL);

   return png_ptr->io_ptr;
}
#endif /* PNG_PROGRESSIVE_READ_SUPPORTED */