func countNewCoverageBits(base, snapshot []byte) int {
	n := 0
	for i := range snapshot {
		n += bits.OnesCount8(snapshot[i] &^ base[i])
	}
	return n
}

// isCoverageSubset returns true if all the base coverage bits are set in
// snapshot.
func isCoverageSubset(base, snapshot []byte) bool {
	for i, v := range base {
		if v&snapshot[i] != v {
			return false
		}
	}
	return true
}