/*
 * (c) Copyright 2009 Talis Information Ltd
 * All rights reserved.
 * [See endLog of file]
 */

package hash;

import com.hp.hpl.jena.tdb.store.Hash ;

import org.openjena.atlas.logging.Log ;

/** From Project Voldemort / Apache License / Thanks! 
 *  who in turn got it from 
 *  
 *  Taken from http://www.isthe.com/chongo/tech/comp/fnv
 * 
 * hash = basis for each octet_of_data to be hashed hash 
 *      = hash * FNV_prime hash
 *      = hash xor octet_of_data return hash
 * 
 */
public class FnvHashFunction implements HashToInt {

    private static final long FNV_BASIS = 0x811c9dc5;
    private static final long FNV_PRIME = (1 << 24) + 0x193;

    @Override
    public int reduce(Hash hash)
    {
        return hash(hash.getBytes()) ;
    }
    
    public int hash(byte[] key) {
        long hash = FNV_BASIS;
        for(int i = 0; i < key.length; i++) {
            hash ^= 0xFF & key[i];
            hash *= FNV_PRIME;
        }

        return (int) hash;
    }

    public static void main(String[] args) {
        if(args.length != 2)
            Log.fatal(FnvHashFunction.class, "USAGE: java FnvHashFunction iterations buckets");
        int numIterations = Integer.parseInt(args[0]);
        int numBuckets = Integer.parseInt(args[1]);
        int[] buckets = new int[numBuckets];
        FnvHashFunction hash = new FnvHashFunction();
        for(int i = 0; i < numIterations; i++) {
            int val = hash.hash(Integer.toString(i).getBytes());
            buckets[Math.abs(val) % numBuckets] += 1;
        }

        double expected = numIterations / (double) numBuckets;
        for(int i = 0; i < numBuckets; i++)
            System.out.println(i + " " + buckets[i] + " " + (buckets[i] / expected));
    }

}

/*
 * (c) Copyright 2009 Talis Information Ltd
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */