    /* pngpread.c - read a png file in push mode
     *
     * Copyright (c) 2018 Cosmin Truta
     * Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson
     * Copyright (c) 1996-1997 Andreas Dilger
     * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
     *
     * This code is released under the libpng license.
     * For conditions of distribution and use, see the disclaimer
     * and license in png.h
     */

    #include "pngpriv.h"

    #ifdef PNG_PROGRESSIVE_READ_SUPPORTED

    /* Push model modes */
    #define PNG_READ_SIG_MODE   0
    #define PNG_READ_CHUNK_MODE 1
    #define PNG_READ_IDAT_MODE  2
    #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

    #define PNG_PUSH_SAVE_BUFFER_IF_FULL \
    if (png_ptr->push_length + 4 > png_ptr->buffer_size) \
       { png_push_save_buffer(png_ptr); return; }
    #define PNG_PUSH_SAVE_BUFFER_IF_LT(N) \
    if (png_ptr->buffer_size < N) \
       { png_push_save_buffer(png_ptr); return; }

    void PNGAPI
    png_process_data(png_structrp png_ptr, png_inforp info_ptr,
        png_bytep buffer, 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);
       }
    }

    size_t PNGAPI
    png_process_data_pause(png_structrp png_ptr, int save)
    {
       if (png_ptr != NULL)
       {
          /* It's easiest for the caller if we do the save; then the caller doesn't
           * have to supply the same data again:
           */
          if (save != 0)
             png_push_save_buffer(png_ptr);
          else
          {
             /* This includes any pending saved bytes: */
             size_t remaining = png_ptr->buffer_size;
             png_ptr->buffer_size = 0;

             /* So subtract the saved buffer size, unless all the data
              * is actually 'saved', in which case we just return 0
              */
             if (png_ptr->save_buffer_size < remaining)
                return remaining - png_ptr->save_buffer_size;
          }
       }

       return 0;
    }

    png_uint_32 PNGAPI
    png_process_data_skip(png_structrp png_ptr)
    {
    /* TODO: Deprecate and remove this API.
     * Somewhere the implementation of this seems to have been lost,
     * or abandoned.  It was only to support some internal back-door access
     * to png_struct) in libpng-1.4.x.
     */
       png_app_warning(png_ptr,
    "png_process_data_skip is not implemented in any current version of libpng");
       return 0;
    }

    /* 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_structrp png_ptr, png_inforp 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;
          }

          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_structrp png_ptr, png_inforp info_ptr)
    {
       size_t num_checked = png_ptr->sig_bytes; /* SAFE, does not exceed 8 */
       size_t 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_structrp png_ptr, png_inforp info_ptr)
    {
       png_uint_32 chunk_name;
    #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
       int keep; /* unknown handling method */
    #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) == 0)
       {
          png_byte chunk_length[4];
          png_byte chunk_tag[4];

          PNG_PUSH_SAVE_BUFFER_IF_LT(8)
          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, chunk_tag, 4);
          png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(chunk_tag);
          png_check_chunk_name(png_ptr, png_ptr->chunk_name);
          png_check_chunk_length(png_ptr, png_ptr->push_length);
          png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;
       }

       chunk_name = png_ptr->chunk_name;

       if (chunk_name == png_IDAT)
       {
          if ((png_ptr->mode & PNG_AFTER_IDAT) != 0)
             png_ptr->mode |= PNG_HAVE_CHUNK_AFTER_IDAT;

          /* 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) == 0)
             png_error(png_ptr, "Missing IHDR before IDAT");

          else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
              (png_ptr->mode & PNG_HAVE_PLTE) == 0)
             png_error(png_ptr, "Missing PLTE before IDAT");

          png_ptr->process_mode = PNG_READ_IDAT_MODE;

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

          png_ptr->mode |= PNG_HAVE_IDAT;

          if ((png_ptr->mode & PNG_AFTER_IDAT) != 0)
             png_benign_error(png_ptr, "Too many IDATs found");
       }

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

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

       else if (chunk_name == png_IEND)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          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 ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length, keep);

          if (chunk_name == png_PLTE)
             png_ptr->mode |= PNG_HAVE_PLTE;
       }
    #endif

       else if (chunk_name == png_PLTE)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_PLTE(png_ptr, info_ptr, png_ptr->push_length);
       }

       else if (chunk_name == png_IDAT)
       {
          png_ptr->idat_size = png_ptr->push_length;
          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_ptr->chunk_name == png_gAMA)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_gAMA(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_sBIT_SUPPORTED
       else if (png_ptr->chunk_name == png_sBIT)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_sBIT(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_cHRM_SUPPORTED
       else if (png_ptr->chunk_name == png_cHRM)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_cHRM(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_sRGB_SUPPORTED
       else if (chunk_name == png_sRGB)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_sRGB(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_iCCP_SUPPORTED
       else if (png_ptr->chunk_name == png_iCCP)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_iCCP(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_sPLT_SUPPORTED
       else if (chunk_name == png_sPLT)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_sPLT(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_tRNS_SUPPORTED
       else if (chunk_name == png_tRNS)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_tRNS(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_bKGD_SUPPORTED
       else if (chunk_name == png_bKGD)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_bKGD(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_hIST_SUPPORTED
       else if (chunk_name == png_hIST)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_hIST(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_pHYs_SUPPORTED
       else if (chunk_name == png_pHYs)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_pHYs(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_oFFs_SUPPORTED
       else if (chunk_name == png_oFFs)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_oFFs(png_ptr, info_ptr, png_ptr->push_length);
       }
    #endif

    #ifdef PNG_READ_pCAL_SUPPORTED
       else if (chunk_name == png_pCAL)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_pCAL(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_sCAL_SUPPORTED
       else if (chunk_name == png_sCAL)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_sCAL(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_tIME_SUPPORTED
       else if (chunk_name == png_tIME)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_tIME(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_tEXt_SUPPORTED
       else if (chunk_name == png_tEXt)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_tEXt(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_zTXt_SUPPORTED
       else if (chunk_name == png_zTXt)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_zTXt(png_ptr, info_ptr, png_ptr->push_length);
       }

    #endif
    #ifdef PNG_READ_iTXt_SUPPORTED
       else if (chunk_name == png_iTXt)
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_iTXt(png_ptr, info_ptr, png_ptr->push_length);
       }
    #endif

       else
       {
          PNG_PUSH_SAVE_BUFFER_IF_FULL
          png_handle_unknown(png_ptr, info_ptr, png_ptr->push_length,
              PNG_HANDLE_CHUNK_AS_DEFAULT);
       }

       png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
    }

    void PNGCBAPI
    png_push_fill_buffer(png_structp png_ptr, png_bytep buffer, size_t length)
    {
       png_bytep ptr;

       if (png_ptr == NULL)
          return;

       ptr = buffer;
       if (png_ptr->save_buffer_size != 0)
       {
          size_t save_size;

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

          else
             save_size = png_ptr->save_buffer_size;

          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 != 0 && png_ptr->current_buffer_size != 0)
       {
          size_t save_size;

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

          else
             save_size = png_ptr->current_buffer_size;

          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_structrp png_ptr)
    {
       if (png_ptr->save_buffer_size != 0)
       {
          if (png_ptr->save_buffer_ptr != png_ptr->save_buffer)
          {
             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)
       {
          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,
              (size_t)new_max);

          if (png_ptr->save_buffer == NULL)
          {
             png_free(png_ptr, old_buffer);
             png_error(png_ptr, "Insufficient memory for save_buffer");
          }

          if (old_buffer)
             memcpy(png_ptr->save_buffer, old_buffer, png_ptr->save_buffer_size);
          else if (png_ptr->save_buffer_size)
             png_error(png_ptr, "save_buffer error");
          png_free(png_ptr, old_buffer);
          png_ptr->save_buffer_max = new_max;
       }
       if (png_ptr->current_buffer_size)
       {
          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_structrp png_ptr, png_bytep buffer,
        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_structrp png_ptr)
    {
       if ((png_ptr->mode & PNG_HAVE_CHUNK_HEADER) == 0)
       {
          png_byte chunk_length[4];
          png_byte chunk_tag[4];

          /* TODO: this code can be commoned up with the same code in push_read */
          PNG_PUSH_SAVE_BUFFER_IF_LT(8)
          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, chunk_tag, 4);
          png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(chunk_tag);
          png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;

          if (png_ptr->chunk_name != png_IDAT)
          {
             png_ptr->process_mode = PNG_READ_CHUNK_MODE;

             if ((png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) == 0)
                png_error(png_ptr, "Not enough compressed data");

             return;
          }

          png_ptr->idat_size = png_ptr->push_length;
       }

       if (png_ptr->idat_size != 0 && png_ptr->save_buffer_size != 0)
       {
          size_t save_size = png_ptr->save_buffer_size;
          png_uint_32 idat_size = png_ptr->idat_size;

          /* We want the smaller of 'idat_size' and 'current_buffer_size', but they
           * are of different types and we don't know which variable has the fewest
           * bits.  Carefully select the smaller and cast it to the type of the
           * larger - this cannot overflow.  Do not cast in the following test - it
           * will break on either 16-bit or 64-bit platforms.
           */
          if (idat_size < save_size)
             save_size = (size_t)idat_size;

          else
             idat_size = (png_uint_32)save_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 -= idat_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 != 0 && png_ptr->current_buffer_size != 0)
       {
          size_t save_size = png_ptr->current_buffer_size;
          png_uint_32 idat_size = png_ptr->idat_size;

          /* We want the smaller of 'idat_size' and 'current_buffer_size', but they
           * are of different types and we don't know which variable has the fewest
           * bits.  Carefully select the smaller and cast it to the type of the
           * larger - this cannot overflow.
           */
          if (idat_size < save_size)
             save_size = (size_t)idat_size;

          else
             idat_size = (png_uint_32)save_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 -= idat_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 == 0)
       {
          PNG_PUSH_SAVE_BUFFER_IF_LT(4)
          png_crc_finish(png_ptr, 0);
          png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
          png_ptr->mode |= PNG_AFTER_IDAT;
          png_ptr->zowner = 0;
       }
    }

    void /* PRIVATE */
    png_process_IDAT_data(png_structrp png_ptr, png_bytep buffer,
        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;
       /* TODO: WARNING: TRUNCATION ERROR: DANGER WILL ROBINSON: */
       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_ZSTREAM_ENDED) == 0)
       {
          int ret;

          /* We have data for zlib, but we must check that zlib
           * has someplace 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))
          {
             /* TODO: WARNING: TRUNCATION ERROR: DANGER WILL ROBINSON: */
             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 (a stream with a missing end code) can still
           * be handled, 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 = PNG_INFLATE(png_ptr, 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_ZSTREAM_ENDED;
             png_ptr->zowner = 0;

             /* 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
             {
                if (ret == Z_DATA_ERROR)
                   png_benign_error(png_ptr, "IDAT: ADLER32 checksum mismatch");
                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_ZSTREAM_ENDED;
                png_ptr->zowner = 0;

                /* 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_ZSTREAM_ENDED;
       }

       /* 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 in IDAT");
    }

    void /* PRIVATE */
    png_push_process_row(png_structrp png_ptr)
    {
       /* 1.5.6: row_info moved out of png_struct to a local here. */
       png_row_info row_info;

       row_info.width = png_ptr->iwidth; /* NOTE: width of current interlaced row */
       row_info.color_type = png_ptr->color_type;
       row_info.bit_depth = png_ptr->bit_depth;
       row_info.channels = png_ptr->channels;
       row_info.pixel_depth = png_ptr->pixel_depth;
       row_info.rowbytes = PNG_ROWBYTES(row_info.pixel_depth, row_info.width);

       if (png_ptr->row_buf[0] > PNG_FILTER_VALUE_NONE)
       {
          if (png_ptr->row_buf[0] < PNG_FILTER_VALUE_LAST)
             png_read_filter_row(png_ptr, &row_info, png_ptr->row_buf + 1,
                png_ptr->prev_row + 1, png_ptr->row_buf[0]);
          else
             png_error(png_ptr, "bad adaptive filter value");
       }

       /* libpng 1.5.6: the following line was copying png_ptr->rowbytes before
        * 1.5.6, while the buffer really is this big in current versions of libpng
        * it may not be in the future, so this was changed just to copy the
        * interlaced row count:
        */
       memcpy(png_ptr->prev_row, png_ptr->row_buf, row_info.rowbytes + 1);

    #ifdef PNG_READ_TRANSFORMS_SUPPORTED
       if (png_ptr->transformations != 0)
          png_do_read_transformations(png_ptr, &row_info);
    #endif

       /* The transformed pixel depth should match the depth now in row_info. */
       if (png_ptr->transformed_pixel_depth == 0)
       {
          png_ptr->transformed_pixel_depth = row_info.pixel_depth;
          if (row_info.pixel_depth > png_ptr->maximum_pixel_depth)
             png_error(png_ptr, "progressive row overflow");
       }

       else if (png_ptr->transformed_pixel_depth != row_info.pixel_depth)
          png_error(png_ptr, "internal progressive row size calculation error");

    #ifdef PNG_READ_INTERLACING_SUPPORTED
       /* Expand interlaced rows to full size */
       if (png_ptr->interlaced != 0 &&
           (png_ptr->transformations & PNG_INTERLACE) != 0)
       {
          if (png_ptr->pass < 6)
             png_do_read_interlace(&row_info, png_ptr->row_buf + 1, png_ptr->pass,
                 png_ptr->transformations);

          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_structrp png_ptr)
    {
    #ifdef PNG_READ_INTERLACING_SUPPORTED
       /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */

       /* Start of interlace block */
       static const png_byte png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};

       /* Offset to next interlace block */
       static const png_byte png_pass_inc[] = {8, 8, 4, 4, 2, 2, 1};

       /* Start of interlace block in the y direction */
       static const png_byte png_pass_ystart[] = {0, 0, 4, 0, 2, 0, 1};

       /* Offset to next interlace block in the y direction */
       static const png_byte 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
       static const png_byte png_pass_height[] = {8, 8, 4, 4, 2, 2, 1};
       */
    #endif

       png_ptr->row_number++;
       if (png_ptr->row_number < png_ptr->num_rows)
          return;

    #ifdef PNG_READ_INTERLACING_SUPPORTED
       if (png_ptr->interlaced != 0)
       {
          png_ptr->row_number = 0;
          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) != 0)
                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 /* READ_INTERLACING */
    }

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

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

    void /* PRIVATE */
    png_push_have_row(png_structrp 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);
    }

    #ifdef PNG_READ_INTERLACING_SUPPORTED
    void PNGAPI
    png_progressive_combine_row(png_const_structrp png_ptr, png_bytep old_row,
        png_const_bytep new_row)
    {
       if (png_ptr == NULL)
          return;

       /* new_row is a flag here - if it is NULL then the app callback was called
        * from an empty row (see the calls to png_struct::row_fn below), otherwise
        * it must be png_ptr->row_buf+1
        */
       if (new_row != NULL)
          png_combine_row(png_ptr, old_row, 1/*blocky display*/);
    }
    #endif /* READ_INTERLACING */

    void PNGAPI
    png_set_progressive_read_fn(png_structrp 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_structrp png_ptr)
    {
       if (png_ptr == NULL)
          return (NULL);

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