Function paethPredictor

depends/lodepng/lodepng.cpp:3974–3981

Paeth predictor, used by PNG filter type 4 The parameters are of type short, but should come from unsigned chars, the shorts are only needed to make the paeth calculation correct. */

are only needed to make the paeth calculation correct.
*/
static unsigned char paethPredictor(short a, short b, short c) {
  short pa = LODEPNG_ABS(b - c);
  short pb = LODEPNG_ABS(a - c);
  short pc = LODEPNG_ABS(a + b - c - c);
  /* return input value associated with smallest of pa, pb, pc (with certain priority if equal) */
  if(pb < pa) { a = b; pa = pb; }
  return (pc < pa) ? c : a;
}

/*shared values used by multiple Adam7 related functions*/