54c73a24b6
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@13550 a1c6a512-1295-4272-9138-f99709370657
93 lines
2.6 KiB
C
93 lines
2.6 KiB
C
/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id: crc32.c 10464 2006-08-05 20:19:10Z miipekk $
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*
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* Copyright (C) 2007 Barry Wardell
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*
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* All files in this archive are subject to the GNU General Public License.
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* See the file COPYING in the source tree root for full license agreement.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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****************************************************************************/
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/*
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* We can't use the CRC32 implementation in the firmware library as it uses a
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* different polynomial. The polynomial needed is 0xEDB88320L
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*
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* CRC32 implementation taken from:
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*
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* efone - Distributed internet phone system.
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*
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* (c) 1999,2000 Krzysztof Dabrowski
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* (c) 1999,2000 ElysiuM deeZine
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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*/
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/* based on implementation by Finn Yannick Jacobs */
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/* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
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* so make sure, you call it before using the other
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* functions!
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*/
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static unsigned int crc_tab[256];
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/* chksum_crc() -- to a given block, this one calculates the
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* crc32-checksum until the length is
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* reached. the crc32-checksum will be
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* the result.
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*/
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unsigned int chksum_crc32 (unsigned char *block, unsigned int length)
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{
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register unsigned long crc;
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unsigned long i;
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crc = 0;
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for (i = 0; i < length; i++)
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{
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crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
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}
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return (crc);
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}
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/* chksum_crc32gentab() -- to a global crc_tab[256], this one will
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* calculate the crcTable for crc32-checksums.
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* it is generated to the polynom [..]
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*/
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void chksum_crc32gentab (void)
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{
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unsigned long crc, poly;
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int i, j;
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poly = 0xEDB88320L;
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for (i = 0; i < 256; i++)
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{
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crc = i;
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for (j = 8; j > 0; j--)
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{
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if (crc & 1)
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{
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crc = (crc >> 1) ^ poly;
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}
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else
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{
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crc >>= 1;
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}
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}
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crc_tab[i] = crc;
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}
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}
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