1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/rt/emul/mini/src/main/java/java/util/zip/Adler32.java Tue Feb 26 16:54:16 2013 +0100
1.3 @@ -0,0 +1,205 @@
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 +}