10个经典的字符串hash函数的C代码实现

               

 

所有内容均来自于：http://www.partow.net/programming/hashfunctions/

以下总共给出了10种字符串hash函数，在上面的链接中可以找到各个Hash函数的描述，以及一些其它的关于hash函数的资料下载。

这些hash函数各自的优缺点不详。其中，ELFHash函数是在unix系统中被广泛使用的，也是《算法艺术与信息学竞赛》中作者推荐的一个字符串hash函数。DEKHash函数是Knuth在其《The Art of Computer Programming》第三卷中引入的。

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 */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 */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 */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 */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 */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 */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 */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 */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 */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 */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 */ 

 

           

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