Old code compiled to
   0x00000000004594a0 <+0>:    lea    -0x1(%rsi),%edx
   0x00000000004594a3 <+3>:    lea    0x1(%rsi),%eax
   0x00000000004594a6 <+6>:    and    $0x1,%esi
   0x00000000004594a9 <+9>:    cmovne %edx,%eax
   0x00000000004594ac <+12>:    retq

New code creates
   0x00000000004594a0 <+0>:    mov    %esi,%eax
   0x00000000004594a2 <+2>:    xor    $0x1,%eax
   0x00000000004594a5 <+5>:    retq

So no conditionals, jumps and fewer instructions

closes #5