// no vector register is larger than 512 bytes for now
	const maxLength = 512
	a := make([]byte, maxLength)
	b := make([]byte, maxLength)
	// randomish but deterministic data. No 0 or 255.
	for i := 0; i < maxLength; i++ {
		a[i] = byte(1 + 31*i%254)
		b[i] = byte(1 + 31*i%254)
	}
	for i := 2; i <= maxLength; i <<= 1 {
		for j := 0; j < i-1; j++ {
			a[j] = b[j] - 1
			a[j+1] = b[j+1] + 1