png_get_fixed_point(png_structrp png_ptr, png_const_bytep buf)
{
   png_uint_32 uval = png_get_uint_32(buf);

   if (uval <= PNG_UINT_31_MAX)
      return (png_fixed_point)uval; /* known to be in range */

   /* The caller can turn off the warning by passing NULL. */
   if (png_ptr != NULL)
      png_warning(png_ptr, "PNG fixed point integer out of range");

   return PNG_FIXED_ERROR;
}

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.