prysm-pulse/shared/testutil/checkbit.go

package testutil

// BitSetCount counts the number of 1s in a byte using the following algo:
// https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
func BitSetCount(bytes []byte) int {
	var total int
	for _, b := range bytes {
		b = (b & 0x55) + ((b >> 1) & 0x55)
		b = (b & 0x33) + ((b >> 2) & 0x33)
		total += int((b + (b >> 4)) & 0xF)
	}
	return total
}

// BitLength returns the length of the bitfield for a giben number of attesters in bytes.
func BitLength(b int) int {
	return (b + 7) / 8
}