查找字符串的哈希方法

查找字符串的哈希方法

比較經典的字符串hash，相信很多使用C的都使用過了吧。


轉貼同學redor的一篇文章，感覺很有用。

//  RS Hash Function
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 )  <<  (BitsInU
nignedInt  -  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 );
}

比較經典的字符串hash就這些了吧,"ELF Hash Function" <-這個比較常用..