常見HASH算法

1. /*  
    ************************************************************************** 
    *                                                                        *  
    *          General Purpose Hash Function Algorithms Library              *  
    *                                                                        *  
    * Author: Arash Partow - 2002                                            *  
    * URL: http://www.partow.net                                             *  
    * URL: http://www.partow.net/programming/hashfunctions/index.html        *  
    *                                                                        *  
    * Copyright notice:                                                      *  
    * Free use of the General Purpose Hash Function Algorithms Library is    *  
    * permitted under the guidelines and in accordance with the most current *  
    * version of the Common Public License.                                  *  
    * http://www.opensource.org/licenses/cpl1.0.php                          *  
    *                                                                        *  
    ************************************************************************** 
   */  
     
     
   class GeneralHashFunctionLibrary   
   {   
     
     
      public long RSHash(String str)   
      {   
         int b     = 378551;   
         int a     = 63689;   
         long hash = 0;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            hash = hash * a + str.charAt(i);   
            a    = a * b;   
         }   
     
         return hash;   
      }   
      /* End Of RS Hash Function */  
     
     
      public long JSHash(String str)   
      {   
         long hash = 1315423911;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            hash ^= ((hash << 5) + str.charAt(i) + (hash >> 2));   
         }   
     
         return hash;   
      }   
      /* End Of JS Hash Function */  
     
     
      public long PJWHash(String str)   
      {   
         long BitsInUnsignedInt = (long)(4 * 8);   
         long ThreeQuarters     = (long)((BitsInUnsignedInt  * 3) / 4);   
         long OneEighth         = (long)(BitsInUnsignedInt / 8);   
         long HighBits          = (long)(0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);   
         long hash              = 0;   
         long test              = 0;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            hash = (hash << OneEighth) + str.charAt(i);   
     
            if((test = hash & HighBits)  != 0)   
            {   
               hash = (( hash ^ (test >> ThreeQuarters)) & (~HighBits));   
            }   
         }   
     
         return hash;   
      }   
      /* End Of  P. J. Weinberger Hash Function */  
     
     
      public long ELFHash(String str)   
      {   
         long hash = 0;   
         long x    = 0;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            hash = (hash << 4) + str.charAt(i);   
     
            if((x = hash & 0xF0000000L) != 0)   
            {   
               hash ^= (x >> 24);   
            }   
            hash &= ~x;   
         }   
     
         return hash;   
      }   
      /* End Of ELF Hash Function */  
     
     
      public long BKDRHash(String str)   
      {   
         long seed = 131; // 31 131 1313 13131 131313 etc..   
         long hash = 0;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            hash = (hash * seed) + str.charAt(i);   
         }   
     
         return hash;   
      }   
      /* End Of BKDR Hash Function */  
     
     
      public long SDBMHash(String str)   
      {   
         long hash = 0;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            hash = str.charAt(i) + (hash << 6) + (hash << 16) - hash;   
         }   
     
         return hash;   
      }   
      /* End Of SDBM Hash Function */  
     
     
      public long DJBHash(String str)   
      {   
         long hash = 5381;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            hash = ((hash << 5) + hash) + str.charAt(i);   
         }   
     
         return hash;   
      }   
      /* End Of DJB Hash Function */  
     
     
      public long DEKHash(String str)   
      {   
         long hash = str.length();   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            hash = ((hash << 5) ^ (hash >> 27)) ^ str.charAt(i);   
         }   
     
         return hash;   
      }   
      /* End Of DEK Hash Function */  
     
     
      public long BPHash(String str)   
      {   
         long hash = 0;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            hash = hash << 7 ^ str.charAt(i);   
         }   
     
         return hash;   
      }   
      /* End Of BP Hash Function */  
     
     
      public long FNVHash(String str)   
      {   
         long fnv_prime = 0x811C9DC5;   
         long hash = 0;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
         hash *= fnv_prime;   
         hash ^= str.charAt(i);   
         }   
     
         return hash;   
      }   
      /* End Of FNV Hash Function */  
     
     
      public long APHash(String str)   
      {   
         long hash = 0xAAAAAAAA;   
     
         for(int i = 0; i < str.length(); i++)   
         {   
            if ((i & 1) == 0)   
            {   
               hash ^= ((hash << 7) ^ str.charAt(i) * (hash >> 3));   
            }   
            else  
            {   
               hash ^= (~((hash << 11) + str.charAt(i) ^ (hash >> 5)));   
            }   
         }   
     
         return hash;   
      }   
      /* End Of AP Hash Function */  
     
   }