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src/Source/LibPNG/pngrutil.c  view on Meta::CPAN

static void
png_read_filter_row_avg(png_row_infop row_info, png_bytep row,
   png_const_bytep prev_row)
{
   png_size_t i;
   png_bytep rp = row;
   png_const_bytep pp = 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++) / 2 )) & 0xff);

      rp++;
   }

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

      rp++;
   }
}

static void
png_read_filter_row_paeth_1byte_pixel(png_row_infop row_info, png_bytep row,
   png_const_bytep prev_row)
{
   png_bytep rp_end = row + row_info->rowbytes;
   int a, c;

   /* First pixel/byte */
   c = *prev_row++;
   a = *row + c;
   *row++ = (png_byte)a;

   /* Remainder */
   while (row < rp_end)
   {
      int b, pa, pb, pc, p;

      a &= 0xff; /* From previous iteration or start */
      b = *prev_row++;

      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

      /* Find the best predictor, the least of pa, pb, pc favoring the earlier
       * ones in the case of a tie.
       */
      if (pb < pa) pa = pb, a = b;
      if (pc < pa) a = c;

      /* Calculate the current pixel in a, and move the previous row pixel to c
       * for the next time round the loop
       */
      c = b;
      a += *row;
      *row++ = (png_byte)a;
   }
}

static void
png_read_filter_row_paeth_multibyte_pixel(png_row_infop row_info, png_bytep row,
   png_const_bytep prev_row)
{
   int bpp = (row_info->pixel_depth + 7) >> 3;
   png_bytep rp_end = row + bpp;

   /* Process the first pixel in the row completely (this is the same as 'up'
    * because there is only one candidate predictor for the first row).
    */
   while (row < rp_end)
   {
      int a = *row + *prev_row++;
      *row++ = (png_byte)a;
   }

   /* Remainder */
   rp_end += row_info->rowbytes - bpp;

   while (row < rp_end)
   {
      int a, b, c, pa, pb, pc, p;

      c = *(prev_row - bpp);
      a = *(row - bpp);
      b = *prev_row++;

      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 (pb < pa) pa = pb, a = b;
      if (pc < pa) a = c;

      a += *row;
      *row++ = (png_byte)a;
   }