hash_test.go

//go:noescape
//go:linkname memhash runtime.memhash
func memhash(p unsafe.Pointer, h, s uintptr) uintptr

type stringStruct struct {
	str unsafe.Pointer
	len int
}

// MemHash is the hash function used by go map, it utilizes available hardware instructions(behaves
// as aeshash if aes instruction is available).
// NOTE: The hash seed changes for every process. So, this cannot be used as a persistent hash.
func MemHash(data []byte) uint64 {
	ss := (*stringStruct)(unsafe.Pointer(&data))
	return uint64(memhash(ss.str, 0, uintptr(ss.len)))
}

func Benchmark_MemHash(b *testing.B) {
	seed := ""
	for i := 0; i < 100; i++ {
		seed += fmt.Sprintf("%v",i)
	}
	for i := 0; i <= b.N; i++ {
		MemHash([]byte(seed))
	}
}


func Benchmark_FNV(b *testing.B) {
	seed := ""
	for i := 0; i < 100; i++ {
		seed += fmt.Sprintf("%v",i)
	}
	hash := fnv.New64()
	for i := 0; i <= b.N; i++ {
		hash.Sum([]byte(seed))
		hash.Sum64()
	}
}

for string len 0:

Benchmark_MemHash-8   	16153923	        76.4 ns/op
Benchmark_FNV-8       	 7797662	       155 ns/op

for string len 1000

Benchmark_MemHash-8   	 2039546	       590 ns/op
Benchmark_FNV-8       	 2523384	       470 ns/op