常用hash算法及评测

常用hash算法及评测 [原创 2010-11-3 11:17:38]

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RS hash 算法

unsigned int RSHash(char* str, unsigned int len)

{

unsigned int b = 378551;

unsigned int a = 63689;

unsigned int hash = 0;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash = hash * a + (*str);

a = a * b;

}

return hash;

}

/* End Of RS Hash Function */

JS hash 算法

unsigned int JSHash(char* str, unsigned int len)

{

unsigned int hash = 1315423911;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash ^= ((hash << 5) + (*str) + (hash >> 2));

}

return hash;

}

/* End Of JS Hash Function */

PJW hash 算法

unsigned int PJWHash(char* str, unsigned int len)

{

const unsigned int BitsInUnsignedInt = (unsigned int)(sizeof(unsigned int) * 8);

const unsigned int ThreeQuarters = (unsigned int)((BitsInUnsignedInt * 3) / 4);

const unsigned int OneEighth = (unsigned int)(BitsInUnsignedInt / 8);

const unsigned int HighBits = (unsigned int)(0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);

unsigned int hash = 0;

unsigned int test = 0;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash = (hash << OneEighth) + (*str);

if((test = hash & HighBits) != 0)

{

hash = (( hash ^ (test >> ThreeQuarters)) & (~HighBits));

}

}

return hash;

}

/* End Of P. J. Weinberger Hash Function */

ELF hash 算法

unsigned int ELFHash(char* str, unsigned int len)

{

unsigned int hash = 0;

unsigned int x = 0;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash = (hash << 4) + (*str);

if((x = hash & 0xF0000000L) != 0)

{

hash ^= (x >> 24);

}

hash &= ~x;

}

return hash;

}

/* End Of ELF Hash Function */

BKDR hash 算法

unsigned int BKDRHash(char* str, unsigned int len)

{

unsigned int seed = 131;

/* 31 131 1313 13131 131313 etc.. */

unsigned int hash = 0;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash = (hash * seed) + (*str);

}

return hash;

}

/* End Of BKDR Hash Function */

SDBM hash 算法

unsigned int SDBMHash(char* str, unsigned int len)

{

unsigned int hash = 0;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash = (*str) + (hash << 6) + (hash << 16) - hash;

}

return hash;

}

/* End Of SDBM Hash Function */

DJB hash 算法

unsigned int DJBHash(char* str, unsigned int len)

{

unsigned int hash = 5381;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash = ((hash << 5) + hash) + (*str);

}

return hash;

}

/* End Of DJB Hash Function */

DEK hash 算法

unsigned int DEKHash(char* str, unsigned int len)

{

unsigned int hash = len;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash = ((hash << 5) ^ (hash >> 27)) ^ (*str);

}

return hash;

}

/* End Of DEK Hash Function */

BP hash 算法

unsigned int BPHash(char* str, unsigned int len)

{

unsigned int hash = 0;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash = hash << 7 ^ (*str);

}

return hash;

}

/* End Of BP Hash Function */

FNV hash 算法

unsigned int FNVHash(char* str, unsigned int len)

{

const unsigned int fnv_prime = 0x811C9DC5;

unsigned int hash = 0;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash *= fnv_prime;

hash ^= (*str);

}

return hash;

}

/* End Of FNV Hash Function */

AP hash 算法

unsigned int APHash(char* str, unsigned int len)

{

unsigned int hash = 0xAAAAAAAA;

unsigned int i = 0;

for(i = 0; i < len; str++, i++)

{

hash ^= ((i & 1) == 0) ? ( (hash << 7) ^ (*str) * (hash >> 3)) :

(~((hash << 11) + (*str) ^ (hash >> 5)));

}

return hash;

}

/* End Of AP Hash Function */

各种算法评测

Hash函数数据1数据2数据3数据4数据1得分数据2得分数据3得分数据4得分平均分BKDRHash20477448196.5510090.9582.0592.64APHash23475449396.5588.4610051.2886.28DJBHash22497547496.5592.31010083.43JSHash14476150610084.6296.8317.9581.94RSHash10486150510010051.5820.5175.96SDBMHash32484950493.192.3157.0123.0872.41PJWHash302648785130043.89021.95ELFHash302648785130043.89021.95

其中

数据1为100000个字母和数字组成的随机串哈希冲突个数。

数据2为100000个有意义的英文句子哈希冲突个数。

数据3为数据1的哈希值与1000003(大素数)求模后存储到线性表中冲突的个数。

数据4为数据1的哈希值与10000019(更大素数)求模后存储到线性表中冲突的个数。

经过比较，得出以上平均得分。平均数为平方平均数。

可以发现，

BKDRHash无论是在实际效果还是编码实现中，效果都是最突出的。

APHash也是较为优秀的算法。DJBHash,JSHash,RSHash与SDBMHash各有千秋。

PJWHash与ELFHash效果最差，但得分相似，其算法本质是相似的。