scale = 0  /* to use integer division */

/* encode Gray code */
define e(i) {
	auto h, r

	if (i <= 0) return 0
	h = i / 2
	r = e(h) * 2                /* recurse */
	if (h % 2 != i % 2) r += 1  /* xor low bits of h, i */
	return r
}

/* decode Gray code */
define d(i) {
	auto h, r

	if (i <= 0) return 0
	h = d(i / 2)                /* recurse */
	r = h * 2
	if (h % 2 != i % 2) r += 1  /* xor low bits of h, i */
	return r
}


/* print i as 5 binary digits */
define p(i) {
	auto d, d[]

	for (d = 0; d <= 4; d++) {
		d[d] = i % 2
		i /= 2
	}
	for (d = 4; d >= 0; d--) {
		if(d[d] == 0) "0"
		if(d[d] == 1) "1"
	}
}

for (i = 0; i < 32; i++) {
	/* original */ t = p(i); " => "
	/* encoded */ e = e(i); t = p(e); " => "
	/* decoded */ d = d(e); t = p(d); "
"
}
quit