xxhash_unsafe.go
func ChecksumString64S(s string, seed uint64) uint64 {
	if len(s) == 0 {
		return Checksum64S(nil, seed)
	}

	ss := (*reflect.StringHeader)(unsafe.Pointer(&s))
	return Checksum64S((*[maxInt32]byte)(unsafe.Pointer(ss.Data))[:len(s):len(s)], seed)
}
func ChecksumString64S(s string, seed uint64) uint64 {
	if len(s) == 0 {
		return Checksum64S(nil, seed)
	}

	ss := (*reflect.StringHeader)(unsafe.Pointer(&s))
	return Checksum64S((*[maxInt32]byte)(unsafe.Pointer(ss.Data))[:len(s):len(s)], seed)
}
// ChecksumString64S returns the checksum of the input data, without creating a copy, with the specific seed.