png_read_filter_row_paeth_multibyte_pixel(png_row_infop row_info, png_bytep row,
    png_const_bytep prev_row)
{
   unsigned 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 = 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;
   }
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.