githubgo-stlhash
algorithm, go, hash, hashcode, list
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  1. 1. 简介
  2. 2. 源码

简介

hashcode 采用map底层的hashcode 方式,提前源码重新封装实现,最大实现hashcode生产效率

源码

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package hash

// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Hashing algorithm inspired by
//   xxhash: https://code.google.com/p/xxhash/
// cityhash: https://code.google.com/p/cityhash/

// +build amd64 amd64p32 arm64 mips64 mips64le ppc64 ppc64le s390x wasm

import (
	"strings"
	"unsafe"
)

const (
	// Constants for multiplication: four random odd 64-bit numbers.
	m1 = 16877499708836156737
	m2 = 2820277070424839065
	m3 = 9497967016996688599
	m4 = 15839092249703872147
)

func add(p unsafe.Pointer, x uintptr) unsafe.Pointer {
	return unsafe.Pointer(uintptr(p) + x)
}
func readUnaligned32(p unsafe.Pointer) uint32 {
	q := (*[4]byte)(p)
	return uint32(q[0]) + uint32(q[1])<<8 + uint32(q[2])<<16 + uint32(q[3])<<24
}
func readUnaligned64(p unsafe.Pointer) uint64 {
	q := (*[8]byte)(p)
	return uint64(q[0]) + uint64(q[1])<<8 + uint64(q[2])<<16 + uint64(q[3])<<24 + uint64(q[4])<<32 + uint64(q[5])<<40 + uint64(q[6])<<48 + uint64(q[7])<<56
}

var hashkey [4]uintptr

type stringStruct struct {
	str unsafe.Pointer
	len int
}

//Strhash (r string)
// return uintptr64
func Strhash(r string) uintptr {
	return memhash(unsafe.Pointer(&r), 3, uintptr(strings.Count(r, "")-1))
}
func memhash(p unsafe.Pointer, seed, s uintptr) uintptr {
	hashkey[0] |= 1 // make sure these numbers are odd
	hashkey[1] |= 1
	hashkey[2] |= 1
	hashkey[3] |= 1
	h := uint64(seed + s*hashkey[0])
tail:
	switch {
	case s == 0:
	case s < 4:
		h ^= uint64(*(*byte)(p))
		h ^= uint64(*(*byte)(add(p, s>>1))) << 8
		h ^= uint64(*(*byte)(add(p, s-1))) << 16
		h = rotl_31(h*m1) * m2
	case s <= 8:
		h ^= uint64(readUnaligned32(p))
		h ^= uint64(readUnaligned32(add(p, s-4))) << 32
		h = rotl_31(h*m1) * m2
	case s <= 16:
		h ^= readUnaligned64(p)
		h = rotl_31(h*m1) * m2
		h ^= readUnaligned64(add(p, s-8))
		h = rotl_31(h*m1) * m2
	case s <= 32:
		h ^= readUnaligned64(p)
		h = rotl_31(h*m1) * m2
		h ^= readUnaligned64(add(p, 8))
		h = rotl_31(h*m1) * m2
		h ^= readUnaligned64(add(p, s-16))
		h = rotl_31(h*m1) * m2
		h ^= readUnaligned64(add(p, s-8))
		h = rotl_31(h*m1) * m2
	default:
		v1 := h
		v2 := uint64(seed * hashkey[1])
		v3 := uint64(seed * hashkey[2])
		v4 := uint64(seed * hashkey[3])
		for s >= 32 {
			v1 ^= readUnaligned64(p)
			v1 = rotl_31(v1*m1) * m2
			p = add(p, 8)
			v2 ^= readUnaligned64(p)
			v2 = rotl_31(v2*m2) * m3
			p = add(p, 8)
			v3 ^= readUnaligned64(p)
			v3 = rotl_31(v3*m3) * m4
			p = add(p, 8)
			v4 ^= readUnaligned64(p)
			v4 = rotl_31(v4*m4) * m1
			p = add(p, 8)
			s -= 32
		}
		h = v1 ^ v2 ^ v3 ^ v4
		goto tail
	}

	h ^= h >> 29
	h *= m3
	h ^= h >> 32
	return uintptr(h)
}

func memhash32(p unsafe.Pointer, seed uintptr) uintptr {
	hashkey[0] |= 1 // make sure these numbers are odd
	hashkey[1] |= 1
	hashkey[2] |= 1
	hashkey[3] |= 1
	h := uint64(seed + 4*hashkey[0])
	v := uint64(readUnaligned32(p))
	h ^= v
	h ^= v << 32
	h = rotl_31(h*m1) * m2
	h ^= h >> 29
	h *= m3
	h ^= h >> 32
	return uintptr(h)
}

func memhash64(p unsafe.Pointer, seed uintptr) uintptr {
	hashkey[0] |= 1 // make sure these numbers are odd
	hashkey[1] |= 1
	hashkey[2] |= 1
	hashkey[3] |= 1
	h := uint64(seed + 8*hashkey[0])
	h ^= uint64(readUnaligned32(p)) | uint64(readUnaligned32(add(p, 4)))<<32
	h = rotl_31(h*m1) * m2
	h ^= h >> 29
	h *= m3
	h ^= h >> 32
	return uintptr(h)
}

// Note: in order to get the compiler to issue rotl instructions, we
// need to constant fold the shift amount by hand.
// TODO: convince the compiler to issue rotl instructions after inlining.
func rotl_31(x uint64) uint64 {
	return (x << 31) | (x >> (64 - 31))
}