code: func multByTwo(out []byte, in []byte) {
  	if len(in) != 16 {
  		panic("len must be 16")
  	}
  	tmp := make([]byte, 16)
  
  	tmp[0] = 2 * in[0]
  	if in[15] >= 128 {
  		tmp[0] = tmp[0] ^ 135
  	}
  	for j := 1; j < 16; j++ {
  		tmp[j] = 2 * in[j]
  		if in[j-1] >= 128 {
  			tmp[j] += 1
  		}
  	}
  	copy(out, tmp)
  }
docs: // multByTwo - GF multiplication as specified in the EME-32 draft