hash.go

package mcache

import (
	"unsafe"

	"github.com/cespare/xxhash/v2"
)

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

func KeyToHash(key interface{}) uint64 {
	if key == nil {
		return 0
	}
	switch k := key.(type) {
	case uint64:
		return k
	case string:
		return MemHashString(k)
	case []byte:
		return MemHash(k)
	case byte:
		return uint64(k)
	case int:
		return uint64(k)
	case int32:
		return uint64(k)
	case uint32:
		return uint64(k)
	case int64:
		return uint64(k)
	default:
		panic("Key type not supported")
	}
}

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)))
}

// MemHashString 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 MemHashString(str string) uint64 {
	ss := (*stringStruct)(unsafe.Pointer(&str))
	return uint64(memhash(ss.str, 0, uintptr(ss.len)))
}

func XXHashString(str string) uint64 {
	return xxhash.Sum64String(str)
}

func Fnv32(key []byte) uint32 {
	hash := uint32(2166136261)
	const prime32 = uint32(16777619)
	keyLength := len(key)
	for i := 0; i < keyLength; i++ {
		hash *= prime32
		hash ^= uint32(key[i])
	}
	return hash
}