哈希函数中同一键的不同值和良好的哈希值排序
Different values for the same key from a hash function and good sort of hash values
我必须执行MurmurHash3，一个哈希函数。但我得到了奇怪的结果。 我想知道我是否使用该功能不好：
杂音哈希3.cpp
#include "MurmurHash3.h"
//-----------------------------------------------------------------------------
// Platform-specific functions and macros
// Microsoft Visual Studio
#if defined(_MSC_VER)
#define FORCE_INLINE __forceinline
#include <stdlib.h>
#define ROTL32(x,y) _rotl(x,y)
#define ROTL64(x,y) _rotl64(x,y)
#define BIG_CONSTANT(x) (x)
// Other compilers
#else // defined(_MSC_VER)
#define FORCE_INLINE inline __attribute__((always_inline))
inline uint32_t rotl32 ( uint32_t x, int8_t r )
{
return (x << r) | (x >> (32 - r));
}
inline uint64_t rotl64 ( uint64_t x, int8_t r )
{
return (x << r) | (x >> (64 - r));
}
#define ROTL32(x,y) rotl32(x,y)
#define ROTL64(x,y) rotl64(x,y)
#define BIG_CONSTANT(x) (x##LLU)
#endif // !defined(_MSC_VER)
//-----------------------------------------------------------------------------
// Block read - if your platform needs to do endian-swapping or can only
// handle aligned reads, do the conversion here
FORCE_INLINE uint32_t getblock32 ( const uint32_t * p, int i )
{
return p[i];
}
FORCE_INLINE uint64_t getblock64 ( const uint64_t * p, int i )
{
return p[i];
}
//-----------------------------------------------------------------------------
// Finalization mix - force all bits of a hash block to avalanche
FORCE_INLINE uint32_t fmix32 ( uint32_t h )
{
h ^= h >> 16;
h *= 0x85ebca6b;
h ^= h >> 13;
h *= 0xc2b2ae35;
h ^= h >> 16;
return h;
}
//----------
FORCE_INLINE uint64_t fmix64 ( uint64_t k )
{
k ^= k >> 33;
k *= BIG_CONSTANT(0xff51afd7ed558ccd);
k ^= k >> 33;
k *= BIG_CONSTANT(0xc4ceb9fe1a85ec53);
k ^= k >> 33;
return k;
}
//-----------------------------------------------------------------------------
void MurmurHash3_x86_128 ( const void * key, const int len,
uint32_t seed, void * out )
{
const uint8_t * data = (const uint8_t*)key;
const int nblocks = len / 16;
uint32_t h1 = seed;
uint32_t h2 = seed;
uint32_t h3 = seed;
uint32_t h4 = seed;
const uint32_t c1 = 0x239b961b;
const uint32_t c2 = 0xab0e9789;
const uint32_t c3 = 0x38b34ae5;
const uint32_t c4 = 0xa1e38b93;
//----------
// body
const uint32_t * blocks = (const uint32_t *)(data + nblocks*16);
for(int i = -nblocks; i; i++)
{
uint32_t k1 = getblock32(blocks,i*4+0);
uint32_t k2 = getblock32(blocks,i*4+1);
uint32_t k3 = getblock32(blocks,i*4+2);
uint32_t k4 = getblock32(blocks,i*4+3);
k1 *= c1; k1 = ROTL32(k1,15); k1 *= c2; h1 ^= k1;
h1 = ROTL32(h1,19); h1 += h2; h1 = h1*5+0x561ccd1b;
k2 *= c2; k2 = ROTL32(k2,16); k2 *= c3; h2 ^= k2;
h2 = ROTL32(h2,17); h2 += h3; h2 = h2*5+0x0bcaa747;
k3 *= c3; k3 = ROTL32(k3,17); k3 *= c4; h3 ^= k3;
h3 = ROTL32(h3,15); h3 += h4; h3 = h3*5+0x96cd1c35;
k4 *= c4; k4 = ROTL32(k4,18); k4 *= c1; h4 ^= k4;
h4 = ROTL32(h4,13); h4 += h1; h4 = h4*5+0x32ac3b17;
}
//----------
// tail
const uint8_t * tail = (const uint8_t*)(data + nblocks*16);
uint32_t k1 = 0;
uint32_t k2 = 0;
uint32_t k3 = 0;
uint32_t k4 = 0;
switch(len & 15)
{
case 15: k4 ^= tail[14] << 16;
case 14: k4 ^= tail[13] << 8;
case 13: k4 ^= tail[12] << 0;
k4 *= c4; k4 = ROTL32(k4,18); k4 *= c1; h4 ^= k4;
case 12: k3 ^= tail[11] << 24;
case 11: k3 ^= tail[10] << 16;
case 10: k3 ^= tail[ 9] << 8;
case 9: k3 ^= tail[ 8] << 0;
k3 *= c3; k3 = ROTL32(k3,17); k3 *= c4; h3 ^= k3;
case 8: k2 ^= tail[ 7] << 24;
case 7: k2 ^= tail[ 6] << 16;
case 6: k2 ^= tail[ 5] << 8;
case 5: k2 ^= tail[ 4] << 0;
k2 *= c2; k2 = ROTL32(k2,16); k2 *= c3; h2 ^= k2;
case 4: k1 ^= tail[ 3] << 24;
case 3: k1 ^= tail[ 2] << 16;
case 2: k1 ^= tail[ 1] << 8;
case 1: k1 ^= tail[ 0] << 0;
k1 *= c1; k1 = ROTL32(k1,15); k1 *= c2; h1 ^= k1;
};
//----------
// finalization
h1 ^= len; h2 ^= len; h3 ^= len; h4 ^= len;
h1 += h2; h1 += h3; h1 += h4;
h2 += h1; h3 += h1; h4 += h1;
h1 = fmix32(h1);
h2 = fmix32(h2);
h3 = fmix32(h3);
h4 = fmix32(h4);
h1 += h2; h1 += h3; h1 += h4;
h2 += h1; h3 += h1; h4 += h1;
((uint32_t*)out)[0] = h1;
((uint32_t*)out)[1] = h2;
((uint32_t*)out)[2] = h3;
((uint32_t*)out)[3] = h4;
}
//-----------------------------------------------------------------------------
void MurmurHash3_x64_128 ( const void * key, const int len,
const uint32_t seed, void * out )
{
const uint8_t * data = (const uint8_t*)key;
const int nblocks = len / 16;
uint64_t h1 = seed;
uint64_t h2 = seed;
const uint64_t c1 = BIG_CONSTANT(0x87c37b91114253d5);
const uint64_t c2 = BIG_CONSTANT(0x4cf5ad432745937f);
//----------
// body
const uint64_t * blocks = (const uint64_t *)(data);
for(int i = 0; i < nblocks; i++)
{
uint64_t k1 = getblock64(blocks,i*2+0);
uint64_t k2 = getblock64(blocks,i*2+1);
k1 *= c1; k1 = ROTL64(k1,31); k1 *= c2; h1 ^= k1;
h1 = ROTL64(h1,27); h1 += h2; h1 = h1*5+0x52dce729;
k2 *= c2; k2 = ROTL64(k2,33); k2 *= c1; h2 ^= k2;
h2 = ROTL64(h2,31); h2 += h1; h2 = h2*5+0x38495ab5;
}
//----------
// tail
const uint8_t * tail = (const uint8_t*)(data + nblocks*16);
uint64_t k1 = 0;
uint64_t k2 = 0;
switch(len & 15)
{
case 15: k2 ^= ((uint64_t)tail[14]) << 48;
case 14: k2 ^= ((uint64_t)tail[13]) << 40;
case 13: k2 ^= ((uint64_t)tail[12]) << 32;
case 12: k2 ^= ((uint64_t)tail[11]) << 24;
case 11: k2 ^= ((uint64_t)tail[10]) << 16;
case 10: k2 ^= ((uint64_t)tail[ 9]) << 8;
case 9: k2 ^= ((uint64_t)tail[ 8]) << 0;
k2 *= c2; k2 = ROTL64(k2,33); k2 *= c1; h2 ^= k2;
case 8: k1 ^= ((uint64_t)tail[ 7]) << 56;
case 7: k1 ^= ((uint64_t)tail[ 6]) << 48;
case 6: k1 ^= ((uint64_t)tail[ 5]) << 40;
case 5: k1 ^= ((uint64_t)tail[ 4]) << 32;
case 4: k1 ^= ((uint64_t)tail[ 3]) << 24;
case 3: k1 ^= ((uint64_t)tail[ 2]) << 16;
case 2: k1 ^= ((uint64_t)tail[ 1]) << 8;
case 1: k1 ^= ((uint64_t)tail[ 0]) << 0;
k1 *= c1; k1 = ROTL64(k1,31); k1 *= c2; h1 ^= k1;
};
//----------
// finalization
h1 ^= len; h2 ^= len;
h1 += h2;
h2 += h1;
h1 = fmix64(h1);
h2 = fmix64(h2);
h1 += h2;
h2 += h1;
((uint64_t*)out)[0] = h1;
((uint64_t*)out)[1] = h2;
}
杂音哈希3.h
#ifndef _MURMURHASH3_H_
#define _MURMURHASH3_H_
//-----------------------------------------------------------------------------
// Platform-specific functions and macros
// Microsoft Visual Studio
#if defined(_MSC_VER) && (_MSC_VER < 1600)
typedef unsigned char uint8_t;
typedef unsigned int uint32_t;
typedef unsigned __int64 uint64_t;
// Other compilers
#else // defined(_MSC_VER)
#include <stdint.h>
#endif // !defined(_MSC_VER)
//-----------------------------------------------------------------------------
void MurmurHash3_x86_32 ( const void * key, int len, uint32_t seed, void * out );
void MurmurHash3_x86_128 ( const void * key, int len, uint32_t seed, void * out );
void MurmurHash3_x64_128 ( const void * key, int len, uint32_t seed, void * out );
//-----------------------------------------------------------------------------
#endif // _MURMURHASH3_H_
测试.cpp
#include "MurmurHash3.h"
#include <time.h>
#include <string.h>
#include <iostream>
using namespace std;
int main ( int argc, char ** argv )
{
const char * hashToTest = "murmur3a";
char out[128] ;
uint32_t seed = time(0);
MurmurHash3_x64_128( hashToTest, strlen(hashToTest) , seed, out );
for(int i=0 ; i<128 ;i++)
cout<<(int) out[i]<<" ";
cout<<endl;
}
我调用该函数MurmurHash3_x64_128因为我使用的是 64 位系统。 如果您使用的是 32 位，则应调用MurmurHash3_x86_128
但是，例如，我进入了
-34 -106 32 -60 34 44 -30 -128 -127 -10 -75 25 73 -64 -50 31 -120 32 96 0 0 0 0 0 41 116 50 -56 7 127 0 0 1 0 0 0 0 0 0 0 -32 -71 12 29 -3 127 0 0 -8 29 96 0 0 0 0 0 68 24 64 0 0 0 0 0 -8 -79 47 -56 7 127 0 0 -1 -1 0 0 1 0 0 0 -16 -71 12 29 -3 127 0 0 89 24 64 0 0 0 0 0 2 0 0 0 0 0 0 0 -83 24 64 0 0 0 0 0 1 0 0 0 -3 127 0 0 0 0 0 0 0 0 0 0
也有负值。我不是哈希函数的专家。这种行为正常吗？ 此外，我需要对从函数的更多调用返回的哈希值进行排序。如何有效地比较哈希值？用异或？
另一件让我觉得我错了的事情是该函数为同一执行返回 2 个不同的哈希值。即看这段代码
测试.cpp
#include "MurmurHash3.h"
#include <time.h>
#include <string.h>
#include <iostream>
using namespace std;
int main ( int argc, char ** argv )
{
const char * hashToTest = "murmur3a";
char out[128] ;
char out2[128] ;
uint32_t seed = time(0);
MurmurHash3_x64_128( hashToTest, strlen(hashToTest) , seed, out );
MurmurHash3_x64_128( hashToTest, strlen(hashToTest) , seed, out2 );
for(int i=0 ; i<128 ;i++)
cout<<(int) out[i]<<" ";
cout<<endl;
for(int i=0 ; i<128 ;i++)
cout<<(int) out2[i]<<" ";
cout<<endl;
}
我得到 2 个不同的哈希值：
-93 -105 98 -119 -121 125 76 -5 -48 -108 51 -50 18 -74 -72 2 -24 -68 37 32 -4 127 0 0 1 0 0 0 0 0 0 0 -80 -69 37 32 -4 127 0 0 -9 102 56 -80 99 127 0 0 1 0 0 0 99 127 0 0 0 0 0 0 0 0 0 0 -80 -81 53 -80 99 127 0 0 -40 40 -53 -81 99 127 0 0 1 0 0 0 0 0 0 0 -80 -69 37 32 -4 127 0 0 -8 29 96 0 0 0 0 0 -91 -42 56 -80 99 127 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0
-93 -105 98 -119 -121 125 76 -5 -48 -108 51 -50 18 -74 -72 2 -128 32 96 0 0 0 0 0 41 100 -50 -81 99 127 0 0 1 0 0 0 0 0 0 0 -80 -69 37 32 -4 127 0 0 -8 29 96 0 0 0 0 0 79 24 64 0 0 0 0 0 -8 -95 -53 -81 99 127 0 0 -1 -1 0 0 1 0 0 0 -64 -69 37 32 -4 127 0 0 100 24 64 0 0 0 0 0 2 0 0 0 0 0 0 0 -67 24 64 0 0 0 0 0 1 0 0 0 -4 127 0 0 0 0 0 0 0 0 0 0
(我正在使用 C++11(
我得到 2 个不同的哈希值：
一个问题是你打印出128字节的数据，但MurmurHash3((只输出128位。 这意味着只有输出每行的第一个 (128/8(=16 个字节是有效的哈希数据;您打印出的剩余字节是没有意义的未初始化/随机数据。
第二个原因在MurmurHash3((维基百科页面上提到：
使用 128 位时，x86 和 x64 版本不会产生相同的结果 值，因为算法针对各自的算法进行了优化 平台。
进入下一部分...
也有负值。我不是哈希函数的专家。 这种行为正常吗？
值是否为负数取决于数据打印机制如何解释字节。 当前，您正在打印值，就好像它们是ints，并且int是有符号数据类型，这意味着任何设置了最高有效位的值都将打印为负值。 如果要查看打印为无符号的值，则应在将它们传递给 cout 之前将它们强制转换为(无符号 int(。
如何有效地比较哈希值？
memcmp(( 是比较两个任意内存缓冲区内容的一种常用方法。
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