in util.go [20:30]
func unsafeUint64SliceToBytes(space []uint64) []byte {
// Get the slice header
header := *(*reflect.SliceHeader)(unsafe.Pointer(&space))
// The length and capacity of the slice are different.
header.Len *= bytesPerWord
header.Cap *= bytesPerWord
// Convert slice header to an []byte
return *(*[]byte)(unsafe.Pointer(&header))
}