Hash.java

package com.bitfire.utils;

/**************************************************************************
 * *
 * 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 *
 * *
 * *************************************************************************
 */

public final class Hash {

	private Hash() {
	}

	public static 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 static 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 static 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 );

			test = hash & HighBits;
			if( test != 0 ) {
				hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
			}
		}

		return hash;
	}

	/* End Of P. J. Weinberger Hash Function */

	public static long ELFHash( String str ) {
		long hash = 0;
		long x = 0;

		for( int i = 0; i < str.length(); i++ ) {
			hash = (hash << 4) + str.charAt( i );

			x = hash & 0xF0000000L;
			if( x != 0 ) {
				hash ^= (x >> 24);
			}
			hash &= ~x;
		}

		return hash;
	}

	/* End Of ELF Hash Function */

	public static 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 static 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 static 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 static 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 static 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 static 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 static 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 */
}