查找字符串的hash算法

最新推荐文章于 2024-02-21 20:51:02 发布

blade2001

最新推荐文章于 2024-02-21 20:51:02 发布

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分类专栏：数据结构及算法文章标签：算法 function string parameters struct table

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本文介绍了多种经典的字符串哈希算法，包括RSHash、JSHash、PJWHash等，并详细展示了每种算法的实现代码。这些算法广泛应用于字符串查找与处理中。

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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;
};