Function CodeShuffle

permutation/code.go:150–189

(perm [base]byte)

}

func CodeShuffle(perm [base]byte) int {
	var state = [base]byte{
		0, 1, 2, 3,
		4, 5, 6, 7,
		8, 9, 10, 11,
	}
	var inverse = [base]byte{
		0, 1, 2, 3,
		4, 5, 6, 7,
		8, 9, 10, 11,
	}
	for i := range perm {
		/*
		 * this cryptic looking code is an optimized version of
		 * this pseudocode:
		 *
		 *     j = inverse[perm[i]]
		 *     swap entries state[i] and state[j] in inverse
		 *     swap entries i and j in state
		 *     perm[i] = j - i
		 *
		 * two optimizations are performed:
		 *  - inverse[state[k]] == k and state[inverse[k]] == k
		 *  - after iteration i, inverse[perm[i]] and state[i]
		 *    are never read again, so we can omit assigning to
		 *    them.
		 */
		j := inverse[perm[i]]
		inverse[state[i]] = j
		state[j] = state[i]
		perm[i] = j - byte(i)
	}

	total := 0
	for i, v := range perm {
		total += int(v) * fact[i]
	}

	return total
}

func CodeShuffleUnroll(perm [base]byte) int {
	var state = [base]byte{