Hash 函數大全

轉自 http://blog.csdn.net/free2o/article/details/2199753  點擊打開鏈接

 看到了幾個Hash 函數的計算方法，因此想把所見到的所有Hash code 的計算方法的算法羅列出來。會陸續追加看到的Hash 的算法。 

第一種：  這是MySql 中計算Hash Code 的一個代碼

inline Uint32 Hash( const char* str ){
  Uint32 h = 0;
  Uint32 len = strlen(str);
  while(len >= 4){
    h = (h << 5) + h + str[0];
    h = (h << 5) + h + str[1];
    h = (h << 5) + h + str[2];
    h = (h << 5) + h + str[3];
    len -= 4;
    str += 4;
  }

  switch(len){
  case 3:
    h = (h << 5) + h + *str++;
  case 2:
    h = (h << 5) + h + *str++;
  case 1:
    h = (h << 5) + h + *str++;
  }
  return h + h;
}

 

 第二種：這是linux 中計算path hash code 的算法

unsigned long hash (const char * str)
{
      unsigned long hs = 0 ;
      while(*str) {hs = (hs + (* str << 4) + ( * str ++ >> 4))  * 11 ;}
      return hs;
}

第三種：這是Java String 類計算Hash code 的算法

int   hash(const char * str,int len)
{
       int h = 0 ,i ;
       for(i = 0 ; i < len ; i ++) ...{
             h = h * 31 + str[i];
       }
}

第四種：OpenSSL 項目中lhash.c 文件提供兩種HashCode 的計算方法

unsigned long lh_strhash(char *str)
{
     int i,l;
    unsigned long ret=0;
    unsigned short *s;

    if (str == NULL) return(0);
    l=(strlen(str)+1)/2;
    s=(unsigned short *)str;
    for (i=0; i<l; i++)
      ret^=(s[i]<<(i&0x0f));
     return(ret);
}

第五種：OpenSSL 項目中lhash.c 文件提供的第兒種HashCode 的計算方法

/* The following hash seems to work very well on normal text strings
 * no collisions on /usr/dict/words and it distributes on %2^n quite
 * well, not as good as MD5, but still good.
 */
unsigned long lh_strhash(const char *c)
    {
    unsigned long ret=0;
    long n;
    unsigned long v;
    int r;

    if ((c == NULL) || (*c == '/0'))
           return(ret);
/*
unsigned char b[16];
MD5(c,strlen(c),b);
return(b[0]|(b[1]<<8)|(b[2]<<16)|(b[3]<<24));
*/

n=0x100;
while (*c)
{
v=n|(*c);
n+=0x100;
r= (int)((v>>2)^v)&0x0f;
ret=(ret<<r)|(ret>>(32-r));
ret&=0xFFFFFFFFL;
ret^=v*v;
c++;
}
return((ret>>16)^ret);
}

第六種：ELF hash 採用的是  DJB (Daniel J Bernstein) hash

uint32_t dl_new_hash (const char *s)
{
        uint32_t h = 5381;

        for (unsigned char c = *s; c != '\0'; c = *++s)
                h = h * 33 + c;
        //h = ((h << 5) + h) + c
        return h;
}