10个经典的字符串hash函数的C代码实现

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 */