HashFunctions.java

/*
 **************************************************************************
 *                                                                        *
 *          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/cpl.php                             *
 *                                                                        *
 **************************************************************************
*/


public class HashFunctions
{


	/** RS hash function -- this is the one we should be using in Numerate */
   public static long RSHash(String str, int maxlength)
   {
      int b     = 378551;
      int a     = 63689;
      long hash = 0;

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); i++)
      {
         hash = hash * a + str.charAt(i);
         a    = a * b;
      }

      return hash;
   }
   /* End Of RS Hash Function */


   public static long JSHash(String str, int maxlength)
   {
      long hash = 1315423911;

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); i++)
      {
         hash ^= ((hash << 5) + str.charAt(i) + (hash >> 2));
      }

      return hash;
   }
   /* End Of JS Hash Function */


   public static long PJWHash(String str, int maxlength)
   {
      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 < maxlength || maxlength <= 0); 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 static long ELFHash(String str, int maxlength)
   {
      long hash = 0;
      long x    = 0;

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); 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 static long BKDRHash(String str, int maxlength)
   {
      long seed = 131; // 31 131 1313 13131 131313 etc..
      long hash = 0;

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); i++)
      {
         hash = (hash * seed) + str.charAt(i);
      }

      return hash;
   }
   /* End Of BKDR Hash Function */


   public static long SDBMHash(String str, int maxlength)
   {
      long hash = 0;

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); i++)
      {
         hash = str.charAt(i) + (hash << 6) + (hash << 16) - hash;
      }

      return hash;
   }
   /* End Of SDBM Hash Function */


   public static long DJBHash(String str, int maxlength)
   {
      long hash = 5381;

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); i++)
      {
         hash = ((hash << 5) + hash) + str.charAt(i);
      }

      return hash;
   }
   /* End Of DJB Hash Function */


   public static long DEKHash(String str, int maxlength)
   {
      long hash = str.length();

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); i++)
      {
         hash = ((hash << 5) ^ (hash >> 27)) ^ str.charAt(i);
      }

      return hash;
   }
   /* End Of DEK Hash Function */


   public static long BPHash(String str, int maxlength)
   {
      long hash = 0;

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); i++)
      {
         hash = hash << 7 ^ str.charAt(i);
      }

      return hash;
   }
   /* End Of BP Hash Function */


   public static long FNVHash(String str, int maxlength)
   {
      long fnv_prime = 0x811C9DC5;
      long hash = 0;

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); i++)
      {
      hash *= fnv_prime;
      hash ^= str.charAt(i);
      }

      return hash;
   }
   /* End Of FNV Hash Function */


   public static long APHash(String str, int maxlength)
   {
      long hash = 0xAAAAAAAA;

      for(int i = 0; i < str.length() && (i < maxlength || maxlength <= 0); 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 */

}