if !testing.Short() {
		lengths = append(lengths, 65535, 65536, 65537, 99999)
	}

	n := lengths[len(lengths)-1]
	a := make([]byte, n+1)
	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