1.1 --- a/emul/mini/src/main/java/java/util/zip/Adler32.java Mon Feb 25 19:00:08 2013 +0100
1.2 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
1.3 @@ -1,205 +0,0 @@
1.4 -/* Adler32.java - Computes Adler32 data checksum of a data stream
1.5 - Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
1.6 -
1.7 -This file is part of GNU Classpath.
1.8 -
1.9 -GNU Classpath is free software; you can redistribute it and/or modify
1.10 -it under the terms of the GNU General Public License as published by
1.11 -the Free Software Foundation; either version 2, or (at your option)
1.12 -any later version.
1.13 -
1.14 -GNU Classpath is distributed in the hope that it will be useful, but
1.15 -WITHOUT ANY WARRANTY; without even the implied warranty of
1.16 -MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
1.17 -General Public License for more details.
1.18 -
1.19 -You should have received a copy of the GNU General Public License
1.20 -along with GNU Classpath; see the file COPYING. If not, write to the
1.21 -Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
1.22 -02111-1307 USA.
1.23 -
1.24 -Linking this library statically or dynamically with other modules is
1.25 -making a combined work based on this library. Thus, the terms and
1.26 -conditions of the GNU General Public License cover the whole
1.27 -combination.
1.28 -
1.29 -As a special exception, the copyright holders of this library give you
1.30 -permission to link this library with independent modules to produce an
1.31 -executable, regardless of the license terms of these independent
1.32 -modules, and to copy and distribute the resulting executable under
1.33 -terms of your choice, provided that you also meet, for each linked
1.34 -independent module, the terms and conditions of the license of that
1.35 -module. An independent module is a module which is not derived from
1.36 -or based on this library. If you modify this library, you may extend
1.37 -this exception to your version of the library, but you are not
1.38 -obligated to do so. If you do not wish to do so, delete this
1.39 -exception statement from your version. */
1.40 -
1.41 -package java.util.zip;
1.42 -
1.43 -/*
1.44 - * Written using on-line Java Platform 1.2 API Specification, as well
1.45 - * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
1.46 - * The actual Adler32 algorithm is taken from RFC 1950.
1.47 - * Status: Believed complete and correct.
1.48 - */
1.49 -
1.50 -/**
1.51 - * Computes Adler32 checksum for a stream of data. An Adler32
1.52 - * checksum is not as reliable as a CRC32 checksum, but a lot faster to
1.53 - * compute.
1.54 - *<p>
1.55 - * The specification for Adler32 may be found in RFC 1950.
1.56 - * (ZLIB Compressed Data Format Specification version 3.3)
1.57 - *<p>
1.58 - *<p>
1.59 - * From that document:
1.60 - *<p>
1.61 - * "ADLER32 (Adler-32 checksum)
1.62 - * This contains a checksum value of the uncompressed data
1.63 - * (excluding any dictionary data) computed according to Adler-32
1.64 - * algorithm. This algorithm is a 32-bit extension and improvement
1.65 - * of the Fletcher algorithm, used in the ITU-T X.224 / ISO 8073
1.66 - * standard.
1.67 - *<p>
1.68 - * Adler-32 is composed of two sums accumulated per byte: s1 is
1.69 - * the sum of all bytes, s2 is the sum of all s1 values. Both sums
1.70 - * are done modulo 65521. s1 is initialized to 1, s2 to zero. The
1.71 - * Adler-32 checksum is stored as s2*65536 + s1 in most-
1.72 - * significant-byte first (network) order."
1.73 - *<p>
1.74 - * "8.2. The Adler-32 algorithm
1.75 - *<p>
1.76 - * The Adler-32 algorithm is much faster than the CRC32 algorithm yet
1.77 - * still provides an extremely low probability of undetected errors.
1.78 - *<p>
1.79 - * The modulo on unsigned long accumulators can be delayed for 5552
1.80 - * bytes, so the modulo operation time is negligible. If the bytes
1.81 - * are a, b, c, the second sum is 3a + 2b + c + 3, and so is position
1.82 - * and order sensitive, unlike the first sum, which is just a
1.83 - * checksum. That 65521 is prime is important to avoid a possible
1.84 - * large class of two-byte errors that leave the check unchanged.
1.85 - * (The Fletcher checksum uses 255, which is not prime and which also
1.86 - * makes the Fletcher check insensitive to single byte changes 0 <->
1.87 - * 255.)
1.88 - *<p>
1.89 - * The sum s1 is initialized to 1 instead of zero to make the length
1.90 - * of the sequence part of s2, so that the length does not have to be
1.91 - * checked separately. (Any sequence of zeroes has a Fletcher
1.92 - * checksum of zero.)"
1.93 - *
1.94 - * @author John Leuner, Per Bothner
1.95 - * @since JDK 1.1
1.96 - *
1.97 - * @see InflaterInputStream
1.98 - * @see DeflaterOutputStream
1.99 - */
1.100 -public class Adler32 implements Checksum
1.101 -{
1.102 -
1.103 - /** largest prime smaller than 65536 */
1.104 - private static final int BASE = 65521;
1.105 -
1.106 - private int checksum; //we do all in int.
1.107 -
1.108 - //Note that java doesn't have unsigned integers,
1.109 - //so we have to be careful with what arithmetic
1.110 - //we do. We return the checksum as a long to
1.111 - //avoid sign confusion.
1.112 -
1.113 - /**
1.114 - * Creates a new instance of the <code>Adler32</code> class.
1.115 - * The checksum starts off with a value of 1.
1.116 - */
1.117 - public Adler32 ()
1.118 - {
1.119 - reset();
1.120 - }
1.121 -
1.122 - /**
1.123 - * Resets the Adler32 checksum to the initial value.
1.124 - */
1.125 - public void reset ()
1.126 - {
1.127 - checksum = 1; //Initialize to 1
1.128 - }
1.129 -
1.130 - /**
1.131 - * Updates the checksum with the byte b.
1.132 - *
1.133 - * @param bval the data value to add. The high byte of the int is ignored.
1.134 - */
1.135 - public void update (int bval)
1.136 - {
1.137 - //We could make a length 1 byte array and call update again, but I
1.138 - //would rather not have that overhead
1.139 - int s1 = checksum & 0xffff;
1.140 - int s2 = checksum >>> 16;
1.141 -
1.142 - s1 = (s1 + (bval & 0xFF)) % BASE;
1.143 - s2 = (s1 + s2) % BASE;
1.144 -
1.145 - checksum = (s2 << 16) + s1;
1.146 - }
1.147 -
1.148 - /**
1.149 - * Updates the checksum with the bytes taken from the array.
1.150 - *
1.151 - * @param buffer an array of bytes
1.152 - */
1.153 - public void update (byte[] buffer)
1.154 - {
1.155 - update(buffer, 0, buffer.length);
1.156 - }
1.157 -
1.158 - /**
1.159 - * Updates the checksum with the bytes taken from the array.
1.160 - *
1.161 - * @param buf an array of bytes
1.162 - * @param off the start of the data used for this update
1.163 - * @param len the number of bytes to use for this update
1.164 - */
1.165 - public void update (byte[] buf, int off, int len)
1.166 - {
1.167 - //(By Per Bothner)
1.168 - int s1 = checksum & 0xffff;
1.169 - int s2 = checksum >>> 16;
1.170 -
1.171 - while (len > 0)
1.172 - {
1.173 - // We can defer the modulo operation:
1.174 - // s1 maximally grows from 65521 to 65521 + 255 * 3800
1.175 - // s2 maximally grows by 3800 * median(s1) = 2090079800 < 2^31
1.176 - int n = 3800;
1.177 - if (n > len)
1.178 - n = len;
1.179 - len -= n;
1.180 - while (--n >= 0)
1.181 - {
1.182 - s1 = s1 + (buf[off++] & 0xFF);
1.183 - s2 = s2 + s1;
1.184 - }
1.185 - s1 %= BASE;
1.186 - s2 %= BASE;
1.187 - }
1.188 -
1.189 - /*Old implementation, borrowed from somewhere:
1.190 - int n;
1.191 -
1.192 - while (len-- > 0) {
1.193 -
1.194 - s1 = (s1 + (bs[offset++] & 0xff)) % BASE;
1.195 - s2 = (s2 + s1) % BASE;
1.196 - }*/
1.197 -
1.198 - checksum = (s2 << 16) | s1;
1.199 - }
1.200 -
1.201 - /**
1.202 - * Returns the Adler32 data checksum computed so far.
1.203 - */
1.204 - public long getValue()
1.205 - {
1.206 - return (long) checksum & 0xffffffffL;
1.207 - }
1.208 -}