func math/bits.Len64

5 uses

	math/bits (current package)
		bits.go#L31: func LeadingZeros64(x uint64) int { return 64 - Len64(x) }
		bits.go#L300: 	return Len64(uint64(x))
		bits.go#L331: func Len64(x uint64) (n int) {

	google.golang.org/protobuf/encoding/protowire
		wire.go#L378: 	return int(9*uint32(bits.Len64(v))+64) / 64

	strconv
		ftoaryu.go#L101: 	if b := bits.Len64(mant); b < 55 {