void /* PRIVATE */
png_write_tIME(png_structp png_ptr, png_timep mod_time)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_tIME;
#endif
   png_byte buf[7];

   png_debug(1, "in png_write_tIME\n");
   if (mod_time->month  > 12 || mod_time->month  < 1 ||
       mod_time->day    > 31 || mod_time->day    < 1 ||
       mod_time->hour   > 23 || mod_time->second > 60)
   {
      png_warning(png_ptr, "Invalid time specified for tIME chunk");
      return;
   }

   png_save_uint_16(buf, mod_time->year);
   buf[2] = mod_time->month;
   buf[3] = mod_time->day;
   buf[4] = mod_time->hour;
   buf[5] = mod_time->minute;
   buf[6] = mod_time->second;

   png_write_chunk(png_ptr, (png_bytep)png_tIME, buf, (png_size_t)7);
}
#endif

/* initializes the row writing capability of libpng */
void /* PRIVATE */
png_write_start_row(png_structp png_ptr)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */

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

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

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

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

   png_size_t buf_size;

   png_debug(1, "in png_write_start_row\n");
   buf_size = (png_size_t)(PNG_ROWBYTES(
      png_ptr->usr_channels*png_ptr->usr_bit_depth,png_ptr->width)+1);

   /* set up row buffer */
   png_ptr->row_buf = (png_bytep)png_malloc(png_ptr, (png_uint_32)buf_size);
   png_ptr->row_buf[0] = PNG_FILTER_VALUE_NONE;

   /* set up filtering buffer, if using this filter */
   if (png_ptr->do_filter & PNG_FILTER_SUB)
   {
      png_ptr->sub_row = (png_bytep)png_malloc(png_ptr,
         (png_ptr->rowbytes + 1));
      png_ptr->sub_row[0] = PNG_FILTER_VALUE_SUB;
   }

   /* We only need to keep the previous row if we are using one of these. */
   if (png_ptr->do_filter & (PNG_FILTER_AVG | PNG_FILTER_UP | PNG_FILTER_PAETH))
   {
     /* set up previous row buffer */
      png_ptr->prev_row = (png_bytep)png_malloc(png_ptr, (png_uint_32)buf_size);
      png_memset(png_ptr->prev_row, 0, buf_size);

      if (png_ptr->do_filter & PNG_FILTER_UP)
      {
         png_ptr->up_row = (png_bytep )png_malloc(png_ptr,
            (png_ptr->rowbytes + 1));
         png_ptr->up_row[0] = PNG_FILTER_VALUE_UP;
      }

      if (png_ptr->do_filter & PNG_FILTER_AVG)
      {
         png_ptr->avg_row = (png_bytep)png_malloc(png_ptr,
            (png_ptr->rowbytes + 1));
         png_ptr->avg_row[0] = PNG_FILTER_VALUE_AVG;
      }

      if (png_ptr->do_filter & PNG_FILTER_PAETH)
      {
         png_ptr->paeth_row = (png_bytep )png_malloc(png_ptr,
            (png_ptr->rowbytes + 1));
         png_ptr->paeth_row[0] = PNG_FILTER_VALUE_PAETH;
      }
   }

#ifdef PNG_WRITE_INTERLACING_SUPPORTED
   /* if interlaced, we need to set up width and height of pass */
   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];
         png_ptr->usr_width = (png_ptr->width + png_pass_inc[0] - 1 -
            png_pass_start[0]) / png_pass_inc[0];
      }
      else
      {
         png_ptr->num_rows = png_ptr->height;
         png_ptr->usr_width = png_ptr->width;
      }
   }
   else
#endif
   {
      png_ptr->num_rows = png_ptr->height;
      png_ptr->usr_width = png_ptr->width;
   }
   png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
   png_ptr->zstream.next_out = png_ptr->zbuf;
}

/* Internal use only.  Called when finished processing a row of data. */
void /* PRIVATE */
png_write_finish_row(png_structp png_ptr)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */

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

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

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

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

   int ret;

   png_debug(1, "in png_write_finish_row\n");
   /* next row */
   png_ptr->row_number++;

   /* see if we are done */
   if (png_ptr->row_number < png_ptr->num_rows)
      return;

#ifdef PNG_WRITE_INTERLACING_SUPPORTED
   /* if interlaced, go to next pass */
   if (png_ptr->interlaced)
   {
      png_ptr->row_number = 0;
      if (png_ptr->transformations & PNG_INTERLACE)
      {
         png_ptr->pass++;
      }
      else
      {
         /* loop until we find a non-zero width or height pass */
         do
         {
            png_ptr->pass++;
            if (png_ptr->pass >= 7)
               break;
            png_ptr->usr_width = (png_ptr->width +
               png_pass_inc[png_ptr->pass] - 1 -
               png_pass_start[png_ptr->pass]) /
               png_pass_inc[png_ptr->pass];
            png_ptr->num_rows = (png_ptr->height +
               png_pass_yinc[png_ptr->pass] - 1 -
               png_pass_ystart[png_ptr->pass]) /
               png_pass_yinc[png_ptr->pass];
            if (png_ptr->transformations & PNG_INTERLACE)
               break;
         } while (png_ptr->usr_width == 0 || png_ptr->num_rows == 0);

      }

      /* reset the row above the image for the next pass */
      if (png_ptr->pass < 7)
      {
         if (png_ptr->prev_row != NULL)
            png_memset(png_ptr->prev_row, 0,
               (png_size_t)(PNG_ROWBYTES(png_ptr->usr_channels*
               png_ptr->usr_bit_depth,png_ptr->width))+1);
         return;
      }
   }
#endif

   /* if we get here, we've just written the last row, so we need
      to flush the compressor */
   do
   {
      /* tell the compressor we are done */
      ret = deflate(&png_ptr->zstream, Z_FINISH);
      /* check for an error */
      if (ret == Z_OK)
      {
         /* check to see if we need more room */
         if (!(png_ptr->zstream.avail_out))
         {
            png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
            png_ptr->zstream.next_out = png_ptr->zbuf;
            png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
         }
      }
      else if (ret != Z_STREAM_END)
      {
         if (png_ptr->zstream.msg != NULL)
            png_error(png_ptr, png_ptr->zstream.msg);
         else
            png_error(png_ptr, "zlib error");
      }
   } while (ret != Z_STREAM_END);

   /* write any extra space */
   if (png_ptr->zstream.avail_out < png_ptr->zbuf_size)
   {
      png_write_IDAT(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size -
         png_ptr->zstream.avail_out);
   }

   deflateReset(&png_ptr->zstream);
}

#if defined(PNG_WRITE_INTERLACING_SUPPORTED)
/* Pick out the correct pixels for the interlace pass.
 * The basic idea here is to go through the row with a source
 * pointer and a destination pointer (sp and dp), and copy the
 * correct pixels for the pass.  As the row gets compacted,
 * sp will always be >= dp, so we should never overwrite anything.
 * See the default: case for the easiest code to understand.
 */
void /* PRIVATE */
png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */

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

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

   png_debug(1, "in png_do_write_interlace\n");
   /* we don't have to do anything on the last pass (6) */
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL && pass < 6)
#else
   if (pass < 6)
#endif
   {
      /* each pixel depth is handled separately */
      switch (row_info->pixel_depth)
      {
         case 1:
         {
            png_bytep sp;
            png_bytep dp;
            int shift;
            int d;
            int value;
            png_uint_32 i;
            png_uint_32 row_width = row_info->width;

            dp = row;
            d = 0;
            shift = 7;
            for (i = png_pass_start[pass]; i < row_width;
               i += png_pass_inc[pass])
            {
               sp = row + (png_size_t)(i >> 3);
               value = (int)(*sp >> (7 - (int)(i & 0x07))) & 0x01;
               d |= (value << shift);

               if (shift == 0)
               {
                  shift = 7;
                  *dp++ = (png_byte)d;
                  d = 0;
               }
               else
                  shift--;

            }
            if (shift != 7)
               *dp = (png_byte)d;
            break;
         }
         case 2:
         {
            png_bytep sp;
            png_bytep dp;
            int shift;
            int d;
            int value;
            png_uint_32 i;
            png_uint_32 row_width = row_info->width;

            dp = row;
            shift = 6;
            d = 0;
            for (i = png_pass_start[pass]; i < row_width;
               i += png_pass_inc[pass])
            {
               sp = row + (png_size_t)(i >> 2);
               value = (*sp >> ((3 - (int)(i & 0x03)) << 1)) & 0x03;
               d |= (value << shift);

               if (shift == 0)
               {
                  shift = 6;
                  *dp++ = (png_byte)d;
                  d = 0;
               }
               else
                  shift -= 2;
            }
            if (shift != 6)
                   *dp = (png_byte)d;
            break;
         }
         case 4:
         {
            png_bytep sp;
            png_bytep dp;
            int shift;
            int d;
            int value;
            png_uint_32 i;
            png_uint_32 row_width = row_info->width;

            dp = row;
            shift = 4;
            d = 0;
            for (i = png_pass_start[pass]; i < row_width;
               i += png_pass_inc[pass])
            {
               sp = row + (png_size_t)(i >> 1);
               value = (*sp >> ((1 - (int)(i & 0x01)) << 2)) & 0x0f;
               d |= (value << shift);

               if (shift == 0)
               {
                  shift = 4;
                  *dp++ = (png_byte)d;
                  d = 0;
               }
               else
                  shift -= 4;
            }
            if (shift != 4)
               *dp = (png_byte)d;
            break;
         }
         default:
         {
            png_bytep sp;
            png_bytep dp;
            png_uint_32 i;
            png_uint_32 row_width = row_info->width;
            png_size_t pixel_bytes;

            /* start at the beginning */
            dp = row;
            /* find out how many bytes each pixel takes up */
            pixel_bytes = (row_info->pixel_depth >> 3);
            /* loop through the row, only looking at the pixels that
               matter */
            for (i = png_pass_start[pass]; i < row_width;
               i += png_pass_inc[pass])
            {
               /* find out where the original pixel is */
               sp = row + (png_size_t)i * pixel_bytes;
               /* move the pixel */
               if (dp != sp)
                  png_memcpy(dp, sp, pixel_bytes);
               /* next pixel */
               dp += pixel_bytes;
            }
            break;
         }
      }
      /* set new row width */
      row_info->width = (row_info->width +
         png_pass_inc[pass] - 1 -
         png_pass_start[pass]) /
         png_pass_inc[pass];
         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
            row_info->width);
   }
}
#endif

/* This filters the row, chooses which filter to use, if it has not already
 * been specified by the application, and then writes the row out with the
 * chosen filter.
 */
#define PNG_MAXSUM (~((png