cityhash–对字符串的哈希算法

原文地址：cityhash–对字符串的哈希算法 – 无敌牛

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分享一个给字符串计算hash的开源库，谷歌出品。

源代码在：https://github.com/google/cityhash

可以自己下载：git clone https://github.com/google/cityhash.git

但是代码是C++的，编译出来的动态库不能在C语言中调用，需要稍做修改后，才能编译出来C语言的动态链接库。

可以按照下边 1.1节的方式修改，也可以直接下载修改完的代码包。

cityhash.tar下载

用 tar -zxvf cityhash.tar.gz 的方式解压，然后从 1.2节开始操作就可以。

编译安装

1.1 修改，使支持C语言调用

只需要修改 src/city.h 文件即可。找到需要在C语言调用的函数，在其前后增加 extern “C” { …. }。修改后的文件如下：

#ifndef CITY_HASH_H_
#define CITY_HASH_H_#include <stdlib.h>  // for size_t.
#include <stdint.h>
#include <utility>typedef uint8_t uint8;
typedef uint32_t uint32;
typedef uint64_t uint64;
typedef std::pair<uint64, uint64> uint128;inline uint64 Uint128Low64(const uint128& x) { return x.first; }
inline uint64 Uint128High64(const uint128& x) { return x.second; }#ifdef __cplusplus
extern "C" {
#endif// Hash function for a byte array.
uint64 CityHash64(const char *buf, size_t len);// Hash function for a byte array.  For convenience, a 64-bit seed is also
// hashed into the result.
uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed);// Hash function for a byte array.  For convenience, two seeds are also
// hashed into the result.
uint64 CityHash64WithSeeds(const char *buf, size_t len,uint64 seed0, uint64 seed1);// Hash function for a byte array.
uint128 CityHash128(const char *s, size_t len);// Hash function for a byte array.  For convenience, a 128-bit seed is also
// hashed into the result.
uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed);// Hash function for a byte array.  Most useful in 32-bit binaries.
uint32 CityHash32(const char *buf, size_t len);#ifdef __cplusplus
}    // extern "C"
#endif// Hash 128 input bits down to 64 bits of output.
// This is intended to be a reasonably good hash function.
inline uint64 Hash128to64(const uint128& x) {// Murmur-inspired hashing.const uint64 kMul = 0x9ddfea08eb382d69ULL;uint64 a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul;a ^= (a >> 47);uint64 b = (Uint128High64(x) ^ a) * kMul;b ^= (b >> 47);b *= kMul;return b;
}#endif  // CITY_HASH_H_

1.2 编译和安装

查看CPU是否支持 sse4_2 指令

生成 Makefile 文件，命令：./configure --enable-sse4.2 。

如果cpu不支持 sse4_2 指令，可以不加参数 --enable-sse4.2 。

编译，命令：make all check CXXFLAGS="-g -O3 -msse4.2" 。

如果cpu不支持 sse4_2 指令，可以不加参数 -msse4.2

安装，命令：make install 动态库会安装在 /usr/local/lib/ 目录，头文件在 /usr/local/include/ 目录。

1.3 增加C语言可引入的头文件

在 /usr/local/include/ 目录下创建 cityhash.h 文件。内容如下：

#ifndef __CITY_HASH_C_H_
#define __CITY_HASH_C_H_#include <stdint.h>typedef uint8_t uint8;
typedef uint32_t uint32;
typedef uint64_t uint64;
typedef struct { uint64_t val[2] ; } uint128;// Hash function for a byte array.
uint64 CityHash64(const char *buf, size_t len);// Hash function for a byte array.  For convenience, a 64-bit seed is also
// hashed into the result.
uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed);// Hash function for a byte array.  For convenience, two seeds are also
// hashed into the result.
uint64 CityHash64WithSeeds(const char *buf, size_t len,uint64 seed0, uint64 seed1);// Hash function for a byte array.
uint128 CityHash128(const char *s, size_t len);// Hash function for a byte array.  For convenience, a 128-bit seed is also
// hashed into the result.
uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed);// Hash function for a byte array.  Most useful in 32-bit binaries.
uint32 CityHash32(const char *buf, size_t len);#endif  //__CITY_HASH_C_H_

测试

2.1 创建测试文件 testch.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>#include "cityhash.h"int test(char * data) ;int main(int argc, char * argv[]){char * data = "aaaaaaaaaaaaaaabbbbbbbbbbbbccccccccccccdddddddddddddeeeeeeeeeeeffffffffffgggggggghhhhhhh" ;test(data) ;char * data2 = "aaaaaaaaaaaaaaabbbbbbbbbbbbccccccccccccdddddddddddddeeeeeeeeeeeffffffffffgggggggghhhhhhh3333" ;test(data2) ;return 0 ;
}int test(char * data) {uint32 key32 = CityHash32(data, strlen(data) ) ;printf("key32 [%u]\n", key32) ;uint64 key64 = CityHash64(data, strlen(data) ) ;printf("key64 [%lu]\n", key64) ;key64 = CityHash64WithSeed(data, strlen(data), 123123123 ) ;printf("key64 [%lu]\n", key64) ;key64 = CityHash64WithSeeds(data, strlen(data), 123123123, 321321321212121) ;printf("key64 [%lu]\n", key64) ;uint128 key128 = CityHash128(data, strlen(data) ) ;printf("key128 [%lu] [%lu]\n", key128.val[0], key128.val[1]) ;uint128 seed ;seed.val[0] = 123123123123 ;seed.val[1] = 33344455556666 ;key128 = CityHash128WithSeed(data, strlen(data),  seed) ;printf("key128 [%lu] [%lu]\n", key128.val[0], key128.val[1]) ;return 0 ;
}