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


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// 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
}