/// near-direct method: rotations with moving mask
unsigned rbN4 (unsigned arg)
{
  __asm
  {
    mov edx, arg    // edx := arg
    mov esi, 10001H // moving mask, starting with 00010001H
    rol edx, 1      // first rotation
    mov eax, esi    // copy mask to do & in-place
    and eax, edx    // apply mask

    mov ecx, 15     // 15 iterations ahead
NEXT:               // loop begin
    rol esi, 1      // next mask
    rol edx, 2      // next rotation
    mov ebx, esi
    and ebx, edx
    or eax, ebx     // store next two bits

    sub ecx, 1
    jnz NEXT        // while ecx != 0
  }
  // return eax
}