/*
 * [TestFNV1a32.java]
 *
 * Summary: Test FNV1a (Fowler/Noll/Vo) 32-bit hashing function.
 *
 * Copyright: (c) 2014-2017 Roedy Green, Canadian Mind Products, http://mindprod.com
 *
 * Licence: This software may be copied and used freely for any purpose but military.
 *          http://mindprod.com/contact/nonmil.html
 *
 * Requires: JDK 1.8+
 *
 * Created with: JetBrains IntelliJ IDEA IDE http://www.jetbrains.com/idea/
 *
 * Version History:
 *  1.0 2014-04-08 initial version
 */
package com.mindprod.example;

import com.mindprod.common18.EIO;

import java.io.UnsupportedEncodingException;

import static java.lang.System.*;

/**
 * Test FNV1a (Fowler/Noll/Vo) 32-bit hashing function.
 *
 * @author Roedy Green, Canadian Mind Products
 * @version 1.0 2014-04-08 initial version
 * @since 2014-04-08
 */
public class TestFNV1a32
    {
    ;

    /**
     * magic 32 bit initial value for the hash = 2,166,136,261
     */
    private static final int MAGIC_OFFSET = ( int ) ( 2_166_136_261L & 0xffffffffL ); /* fake unsigned 32 bit */

    /**
     * prime specified to use in 32 bit hashes
     */
    private static final int MAGIC_PRIME = 16_777_619; /* magic 32 bit FNV_prime = 2^24 + 2^8 + 0x93 = 16,777,619 */

    /**
     * Calc 32 bit FNV1a digest of an array of bytes.
     *
     * @param theTextToDigestAsBytes byte array to compute checksum on
     *
     * @return 32-bit signed fnv1a checksum
     */
    private static int fnv1a32( byte[] theTextToDigestAsBytes )
        {
        int hash = MAGIC_OFFSET;
        for ( byte b : theTextToDigestAsBytes )
            {
            hash ^= b;
            hash *= MAGIC_PRIME;
            }
        return hash;
        }

    /**
     * Test harness
     * see http://isthe.com/chongo/tech/comp/fnv/#FNV-1a
     *
     * @param args not used
     *
     * @throws java.io.UnsupportedEncodingException in case UTF-8 support is missing.
     */
    public static void main( String[] args ) throws UnsupportedEncodingException
        {
        final String s = "The quick brown fox jumped over the lazy dog's back; sample url: http://mindprod.com/jgloss/digest.html";
        final byte[] theTextToDigestAsBytes = s.getBytes( EIO.UTF8 );
        out.println( fnv1a32( theTextToDigestAsBytes ) );
        long start = System.nanoTime();
        for ( int i = 0; i < 100_000; i++ )
            {
            fnv1a32( theTextToDigestAsBytes );
            }
        long stop = System.nanoTime();
        out.println( ( stop - start ) / 1_000_000L + " seconds to compute 100,000 FNV1a32 hashes" );
        // On my machine it takes: 20 seconds to compute 100,000 FNV1a64 hashes
        }
    }