001/*
002 *                    BioJava development code
003 *
004 * This code may be freely distributed and modified under the
005 * terms of the GNU Lesser General Public Licence.  This should
006 * be distributed with the code.  If you do not have a copy,
007 * see:
008 *
009 *      http://www.gnu.org/copyleft/lesser.html
010 *
011 * Copyright for this code is held jointly by the individual
012 * authors.  These should be listed in @author doc comments.
013 *
014 * For more information on the BioJava project and its aims,
015 * or to join the biojava-l mailing list, visit the home page
016 * at:
017 *
018 *      http://www.biojava.org/
019 *
020 */
021
022package org.biojavax.utils;
023
024import java.util.zip.Checksum;
025
026/**
027 * Utility class that calculates a CRC64 checksum on a stream of bytes. Code was
028 * based on some from BioPerl. Note that we use longs then cast them to avoid
029 * the lack of an unsigned int in Java. Longs are 64-bit but we are only using
030 * the bottom 32 bits. An int is 32-bit but encodes sign so we can get amusing
031 * results if we don't allow for this.
032 * 
033 * @author Unknown. Copied from Expasy4J for convenience. See <a
034 *         href="http://dev.isb-sib.ch/projects/expasy4j/">http://dev.isb-sib.ch/projects/expasy4j/</a>
035 * @since 1.5
036 */
037public class CRC64Checksum implements Checksum {
038        private static final long POLY64 = 0xD800000000000000L;
039
040        private static final long[] crcTable = new long[256];
041
042        private long crc;
043
044        static {
045                for (int i = 0; i < 256; ++i) {
046                        long part = i;
047                        for (int j = 0; j < 8; ++j)
048                                part = ((part & 1) != 0) ? (part >>> 1) ^ POLY64 : (part >>> 1);
049                        crcTable[i] = part;
050                }
051        }
052
053        public void update(int b) {
054                long low = crc >>> 8;
055                long high = crcTable[(int) ((crc ^ b) & 0xFF)];
056                crc = low ^ high;
057        }
058
059        public void update(byte[] b, int offset, int length) {
060                for (int i = offset; i < length; ++i)
061                        update(b[i]);
062        }
063
064        public void update(String s) {
065                // update(s.getBytes(), 0, s.length());
066                int size = s.length();
067                for (int i = 0; i < size; ++i)
068                        update(s.charAt(i));
069
070        }
071
072        public long getValue() {
073                return crc;
074        }
075
076        /**
077         * Returns a zero-padded 16 character wide string containing the current
078         * value of this checksum in uppercase hexadecimal format.
079         */
080        public String toString() {
081                StringBuffer builder = new StringBuffer();
082                builder.append(Long.toHexString(crc >>> 4));
083                builder.append(Long.toHexString(crc & 0xF));
084                for (int i = 16 - builder.length(); i > 0; --i)
085                        builder.insert(0, '0');
086                return builder.toString().toUpperCase();
087        }
088
089        public void reset() {
090                crc = 0;
091        }
092}