| 1 | /* Adler32.java - Computes Adler32 data checksum of a data stream
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| 2 | Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
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| 3 |
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| 4 | This file is part of GNU Classpath.
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| 5 |
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| 6 | GNU Classpath is free software; you can redistribute it and/or modify
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| 7 | it under the terms of the GNU General Public License as published by
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| 8 | the Free Software Foundation; either version 2, or (at your option)
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| 9 | any later version.
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| 10 |
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| 11 | GNU Classpath is distributed in the hope that it will be useful, but
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| 12 | WITHOUT ANY WARRANTY; without even the implied warranty of
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| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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| 14 | General Public License for more details.
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| 15 |
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| 16 | You should have received a copy of the GNU General Public License
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| 17 | along with GNU Classpath; see the file COPYING. If not, write to the
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| 18 | Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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| 19 | 02111-1307 USA.
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| 20 |
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| 21 | Linking this library statically or dynamically with other modules is
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| 22 | making a combined work based on this library. Thus, the terms and
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| 23 | conditions of the GNU General Public License cover the whole
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| 24 | combination.
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| 25 |
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| 26 | As a special exception, the copyright holders of this library give you
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| 27 | permission to link this library with independent modules to produce an
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| 28 | executable, regardless of the license terms of these independent
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| 29 | modules, and to copy and distribute the resulting executable under
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| 30 | terms of your choice, provided that you also meet, for each linked
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| 31 | independent module, the terms and conditions of the license of that
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| 32 | module. An independent module is a module which is not derived from
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| 33 | or based on this library. If you modify this library, you may extend
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| 34 | this exception to your version of the library, but you are not
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| 35 | obligated to do so. If you do not wish to do so, delete this
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| 36 | exception statement from your version. */
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| 37 |
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| 38 | package java.util.zip;
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| 39 |
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| 40 | /*
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| 41 | * Written using on-line Java Platform 1.2 API Specification, as well
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| 42 | * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
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| 43 | * The actual Adler32 algorithm is taken from RFC 1950.
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| 44 | * Status: Believed complete and correct.
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| 45 | */
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| 46 |
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| 47 | /**
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| 48 | * Computes Adler32 checksum for a stream of data. An Adler32
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| 49 | * checksum is not as reliable as a CRC32 checksum, but a lot faster to
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| 50 | * compute.
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| 51 | *<p>
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| 52 | * The specification for Adler32 may be found in RFC 1950.
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| 53 | * (ZLIB Compressed Data Format Specification version 3.3)
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| 54 | *<p>
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| 55 | *<p>
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| 56 | * From that document:
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| 57 | *<p>
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| 58 | * "ADLER32 (Adler-32 checksum)
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| 59 | * This contains a checksum value of the uncompressed data
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| 60 | * (excluding any dictionary data) computed according to Adler-32
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| 61 | * algorithm. This algorithm is a 32-bit extension and improvement
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| 62 | * of the Fletcher algorithm, used in the ITU-T X.224 / ISO 8073
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| 63 | * standard.
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| 64 | *<p>
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| 65 | * Adler-32 is composed of two sums accumulated per byte: s1 is
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| 66 | * the sum of all bytes, s2 is the sum of all s1 values. Both sums
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| 67 | * are done modulo 65521. s1 is initialized to 1, s2 to zero. The
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| 68 | * Adler-32 checksum is stored as s2*65536 + s1 in most-
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| 69 | * significant-byte first (network) order."
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