func maphash64(s string) uint64 {
	if s == "" {
		return maphashSeed
	}
	strh := (*reflect.StringHeader)(unsafe.Pointer(&s))
	return uint64(memhash(unsafe.Pointer(strh.Data), maphashSeed, uintptr(strh.Len)))
}
exposes the built-in memhash function
package xsync
import (
	"reflect"
	"unsafe"
)
const (
	cacheLineSize = 64
	maphashSeed = 42
)
func hash64(x uintptr) uint64 {
	x = ((x >> 33) ^ x) * 0xff51afd7ed558ccd
	x = ((x >> 33) ^ x) * 0xc4ceb9fe1a85ec53
	x = (x >> 33) ^ x
	return uint64(x)
}