forgejo/vendor/github.com/syndtr/goleveldb/leveldb/util/hash.go

// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package util

import (
	"encoding/binary"
)

// Hash return hash of the given data.
func Hash(data []byte, seed uint32) uint32 {
	// Similar to murmur hash
	const (
		m = uint32(0xc6a4a793)
		r = uint32(24)
	)
	var (
		h = seed ^ (uint32(len(data)) * m)
		i int
	)

	for n := len(data) - len(data)%4; i < n; i += 4 {
		h += binary.LittleEndian.Uint32(data[i:])
		h *= m
		h ^= (h >> 16)
	}

	switch len(data) - i {
	default:
		panic("not reached")
	case 3:
		h += uint32(data[i+2]) << 16
		fallthrough
	case 2:
		h += uint32(data[i+1]) << 8
		fallthrough
	case 1:
		h += uint32(data[i])
		h *= m
		h ^= (h >> r)
	case 0:
	}

	return h
}