+++ /dev/null
-/* Adler32.java - Computes Adler32 data checksum of a data stream
- Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
-
-This file is part of GNU Classpath.
-
-GNU Classpath is free software; you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 2, or (at your option)
-any later version.
-
-GNU Classpath is distributed in the hope that it will be useful, but
-WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
-General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with GNU Classpath; see the file COPYING. If not, write to the
-Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
-02111-1307 USA.
-
-Linking this library statically or dynamically with other modules is
-making a combined work based on this library. Thus, the terms and
-conditions of the GNU General Public License cover the whole
-combination.
-
-As a special exception, the copyright holders of this library give you
-permission to link this library with independent modules to produce an
-executable, regardless of the license terms of these independent
-modules, and to copy and distribute the resulting executable under
-terms of your choice, provided that you also meet, for each linked
-independent module, the terms and conditions of the license of that
-module. An independent module is a module which is not derived from
-or based on this library. If you modify this library, you may extend
-this exception to your version of the library, but you are not
-obligated to do so. If you do not wish to do so, delete this
-exception statement from your version. */
-
-package java.util.zip;
-
-/*
- * Written using on-line Java Platform 1.2 API Specification, as well
- * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
- * The actual Adler32 algorithm is taken from RFC 1950.
- * Status: Believed complete and correct.
- */
-
-/**
- * Computes Adler32 checksum for a stream of data. An Adler32
- * checksum is not as reliable as a CRC32 checksum, but a lot faster to
- * compute.
- *<p>
- * The specification for Adler32 may be found in RFC 1950.
- * (ZLIB Compressed Data Format Specification version 3.3)
- *<p>
- *<p>
- * From that document:
- *<p>
- * "ADLER32 (Adler-32 checksum)
- * This contains a checksum value of the uncompressed data
- * (excluding any dictionary data) computed according to Adler-32
- * algorithm. This algorithm is a 32-bit extension and improvement
- * of the Fletcher algorithm, used in the ITU-T X.224 / ISO 8073
- * standard.
- *<p>
- * Adler-32 is composed of two sums accumulated per byte: s1 is
- * the sum of all bytes, s2 is the sum of all s1 values. Both sums
- * are done modulo 65521. s1 is initialized to 1, s2 to zero. The
- * Adler-32 checksum is stored as s2*65536 + s1 in most-
- * significant-byte first (network) order."
- *<p>
- * "8.2. The Adler-32 algorithm
- *<p>
- * The Adler-32 algorithm is much faster than the CRC32 algorithm yet
- * still provides an extremely low probability of undetected errors.
- *<p>
- * The modulo on unsigned long accumulators can be delayed for 5552
- * bytes, so the modulo operation time is negligible. If the bytes
- * are a, b, c, the second sum is 3a + 2b + c + 3, and so is position
- * and order sensitive, unlike the first sum, which is just a
- * checksum. That 65521 is prime is important to avoid a possible
- * large class of two-byte errors that leave the check unchanged.
- * (The Fletcher checksum uses 255, which is not prime and which also
- * makes the Fletcher check insensitive to single byte changes 0 <->
- * 255.)
- *<p>
- * The sum s1 is initialized to 1 instead of zero to make the length
- * of the sequence part of s2, so that the length does not have to be
- * checked separately. (Any sequence of zeroes has a Fletcher
- * checksum of zero.)"
- *
- * @author John Leuner, Per Bothner
- * @since JDK 1.1
- *
- * @see InflaterInputStream
- * @see DeflaterOutputStream
- */
-public class Adler32 implements Checksum
-{
-
- /** largest prime smaller than 65536 */
- private static final int BASE = 65521;
-
- private int checksum; //we do all in int.
-
- //Note that java doesn't have unsigned integers,
- //so we have to be careful with what arithmetic
- //we do. We return the checksum as a long to
- //avoid sign confusion.
-
- /**
- * Creates a new instance of the <code>Adler32</code> class.
- * The checksum starts off with a value of 1.
- */
- public Adler32 ()
- {
- reset();
- }
-
- /**
- * Resets the Adler32 checksum to the initial value.
- */
- public void reset ()
- {
- checksum = 1; //Initialize to 1
- }
-
- /**
- * Updates the checksum with the byte b.
- *
- * @param bval the data value to add. The high byte of the int is ignored.
- */
- public void update (int bval)
- {
- //We could make a length 1 byte array and call update again, but I
- //would rather not have that overhead
- int s1 = checksum & 0xffff;
- int s2 = checksum >>> 16;
-
- s1 = (s1 + (bval & 0xFF)) % BASE;
- s2 = (s1 + s2) % BASE;
-
- checksum = (s2 << 16) + s1;
- }
-
- /**
- * Updates the checksum with the bytes taken from the array.
- *
- * @param buffer an array of bytes
- */
- public void update (byte[] buffer)
- {
- update(buffer, 0, buffer.length);
- }
-
- /**
- * Updates the checksum with the bytes taken from the array.
- *
- * @param buf an array of bytes
- * @param off the start of the data used for this update
- * @param len the number of bytes to use for this update
- */
- public void update (byte[] buf, int off, int len)
- {
- //(By Per Bothner)
- int s1 = checksum & 0xffff;
- int s2 = checksum >>> 16;
-
- while (len > 0)
- {
- // We can defer the modulo operation:
- // s1 maximally grows from 65521 to 65521 + 255 * 3800
- // s2 maximally grows by 3800 * median(s1) = 2090079800 < 2^31
- int n = 3800;
- if (n > len)
- n = len;
- len -= n;
- while (--n >= 0)
- {
- s1 = s1 + (buf[off++] & 0xFF);
- s2 = s2 + s1;
- }
- s1 %= BASE;
- s2 %= BASE;
- }
-
- /*Old implementation, borrowed from somewhere:
- int n;
-
- while (len-- > 0) {
-
- s1 = (s1 + (bs[offset++] & 0xff)) % BASE;
- s2 = (s2 + s1) % BASE;
- }*/
-
- checksum = (s2 << 16) | s1;
- }
-
- /**
- * Returns the Adler32 data checksum computed so far.
- */
- public long getValue()
- {
- return (long) checksum & 0xffffffffL;
- }
-}
projects / msp430-gcc.git / blobdiff