b := make([]byte, n+1)
	for _, len := range lengths {
		// randomish but deterministic data. No 0 or 255.
		for i := 0; i < len; i++ {
			a[i] = byte(1 + 31*i%254)
			b[i] = byte(1 + 31*i%254)
		}
		// data past the end is different
		for i := len; i <= n; i++ {
			a[i] = 8
			b[i] = 9
		}
		cmp := Compare(a[:len], b[:len])
		if cmp != 0 {
			t.Errorf(`CompareIdentical(%d) = %d`, len, cmp)
		}
		if len > 0 {