字符串的hash算法[转]

查找字符串的hash算法

unsigned  int  RSHash( char   * str)
  {
        unsigned  int  b  =   378551 ;
        unsigned  int  a  =   63689 ;
        unsigned  int  hash  =   0 ;

         while  ( * str)
          {
                hash  =  hash  *  a  +  ( * str ++ );
                a  *=  b;
        } 
 
         return  (hash  &   0x7FFFFFFF );
} 
 
 //  JS Hash Function 
 unsigned  int  JSHash( char   * str)
  {
        unsigned  int  hash  =   1315423911 ;

         while  ( * str)
          {
                hash  ^=  ((hash  <<   5 )  +  ( * str ++ )  +  (hash  >>   2 ));
        } 
 
         return  (hash  &   0x7FFFFFFF );
} 
 
 //  P. J. Weinberger Hash Function 
 unsigned  int  PJWHash( char   * str)
  {
        unsigned  int  BitsInUnignedInt  =  (unsigned  int )( sizeof (unsigned  int )  * 
 8 );
        unsigned  int  ThreeQuarters     =  (unsigned  int )((BitsInUnignedInt   *   3 )
  /   4 );
        unsigned  int  OneEighth         =  (unsigned  int )(BitsInUnignedInt  /   8 );

        unsigned  int  HighBits          =  (unsigned  int )( 0xFFFFFFFF )  <<  (BitsInUnignedInt  -  OneEighth);
        unsigned  int  hash              =   0 ;
        unsigned  int  test              =   0 ;

         while  ( * str)
          {
                hash  =  (hash  <<  OneEighth)  +  ( * str ++ );
                 if  ((test  =  hash  &  HighBits)  !=   0 )
                  {
                        hash  =  ((hash  ^  (test  >>  ThreeQuarters))  &  ( ~ HighBits));
                  } 
        } 
 
         return  (hash  &   0x7FFFFFFF );
} 
 
 //  ELF Hash Function 
 unsigned  int  ELFHash( char   * str)
  {
        unsigned  int  hash  =   0 ;
        unsigned  int  x     =   0 ;

         while  ( * str)
          {
                 hash  =  (hash  <<   4 )  +  ( * str ++ );
                 if  ((x  =  hash  &   0xF0000000L )  !=   0 )
                  {
                        hash  ^=  (x  >>   24 );
                        hash  &=   ~ x;
                } 
        } 
 
         return  (hash  &   0x7FFFFFFF );
} 
 
 //  BKDR Hash Function 
 unsigned  int  BKDRHash( char   * str)
  {
        unsigned  int  seed  =   131 ;  //  31 131 1313 13131 131313 etc.. 
         unsigned  int  hash  =   0 ;

         while  ( * str)
          {
                hash  =  hash  *  seed  +  ( * str ++ );
          } 
 
         return  (hash  &   0x7FFFFFFF );
} 
 
 //  SDBM Hash Function 
 unsigned  int  SDBMHash( char   * str)
  {
        unsigned  int  hash  =   0 ;

         while  ( * str)
          {
                hash  =  ( * str ++ )  +  (hash  <<   6 )  +  (hash  <<   16 )  -  hash;
          } 
 
         return  (hash  &   0x7FFFFFFF );
} 
 
 //  DJB Hash Function 
 unsigned  int  DJBHash( char   * str)
  {
        unsigned  int  hash  =   5381 ;

         while  ( * str)
          {
                hash  +=  (hash  <<   5 )  +  ( * str ++ );
          } 
 
         return  (hash  &   0x7FFFFFFF );
} 
 
 //  AP Hash Function 
 unsigned  int  APHash( char   * str)
  {
        unsigned  int  hash  =   0 ;
         int  i;

         for  (i = 0 ;  * str; i ++ )
          {
                 if  ((i  &   1 )  ==   0 )
                  {
                        hash  ^=  ((hash  <<   7 )  ^  ( * str ++ )  ^  (hash  >>   3 ));
                  } 
                 else 
                  {
                        hash  ^=  ( ~ ((hash  <<   11 )  ^  ( * str ++ )  ^  (hash  >>   5 )));
                  } 
        } 
 
         return  (hash  &   0x7FFFFFFF );
} 

struct hash_map_func
{
    enum
    {    // parameters for hash table
        bucket_size = 2,    // 0 < bucket_size
        min_buckets = 8
    };    // min_buckets = 2 ^^ N, 0 < N
    size_t operator()(const string& str)const
    {
        const char* p =str.c_str();
        unsigned long hash = 5381;
        int c;
        while (c = *p++)
            hash = ((hash << 5) + hash) + c; /**//* hash * 33 + c */
        return hash;
    }
    bool operator()(const string& _Keyval1, const string& _Keyval2) const
    {    // test if _Keyval1 ordered before _Keyval2
        return (gt(_Keyval1, _Keyval2));
    }
    greater<string> gt;
};

较经典的字符串hash就这些了吧,"ELF Hash Function" <-这个比较常用..