png_init_filter_functions(png_structrp pp)
   /* This function is called once for every PNG image (except for PNG images
    * that only use PNG_FILTER_VALUE_NONE for all rows) to set the
    * implementations required to reverse the filtering of PNG rows.  Reversing
    * the filter is the first transformation performed on the row data.  It is
    * performed in place, therefore an implementation can be selected based on
    * the image pixel format.  If the implementation depends on image width then
    * take care to ensure that it works correctly if the image is interlaced -
    * interlacing causes the actual row width to vary.
    */
{
   unsigned int bpp = (pp->pixel_depth + 7) >> 3;

   pp->read_filter[PNG_FILTER_VALUE_SUB-1] = png_read_filter_row_sub;
   pp->read_filter[PNG_FILTER_VALUE_UP-1] = png_read_filter_row_up;
   pp->read_filter[PNG_FILTER_VALUE_AVG-1] = png_read_filter_row_avg;
   if (bpp == 1)
      pp->read_filter[PNG_FILTER_VALUE_PAETH-1] =
         png_read_filter_row_paeth_1byte_pixel;
   else
      pp->read_filter[PNG_FILTER_VALUE_PAETH-1] =
         png_read_filter_row_paeth_multibyte_pixel;

#ifdef PNG_FILTER_OPTIMIZATIONS
   /* To use this define PNG_FILTER_OPTIMIZATIONS as the name of a function to
    * call to install hardware optimizations for the above functions; simply
    * replace whatever elements of the pp->read_filter[] array with a hardware
    * specific (or, for that matter, generic) optimization.
    *
    * To see an example of this examine what configure.ac does when
    * --enable-arm-neon is specified on the command line.
    */
   PNG_FILTER_OPTIMIZATIONS(pp, bpp);
#endif
}

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.