OLD SCHOOL!

gistfile1.c

static RADFORCEINLINE U32 linear_mix_50(U32 a, U32 b)
{
  return (a | b) - (((a ^ b) >> 1) & 0x7f7f7f7f);
}

static void linear_8x8_50_50(char unsigned * RADRESTRICT dest, int dw, char unsigned * RADRESTRICT src_near, char unsigned * RADRESTRICT src_far, int sw)
{
  int y;

  for( y = 0 ; y < 8 ; y++, src_near += sw, src_far += sw, dest += dw )
  {
    U32 const * RADRESTRICT srcn32 = (U32 const *) src_near;
    U32 const * RADRESTRICT srcf32 = (U32 const *) src_far;
    U32 * RADRESTRICT dst32 = (U32 *) dest;

    dst32[0] = linear_mix_50(srcn32[0], srcf32[0]);
    dst32[1] = linear_mix_50(srcn32[1], srcf32[1]);
  }
}