fc92081080
This uses the reverse of the polynomial used by the current crc_32 function. The code for this was derived from the implementation used by tinf. This version is space optimized and should be a good way to reduce code duplication in other parts of rockbox that use the same crc32 algorithm. This is mainly of use in areas where DEFLATE is in use. Change-Id: I918da5b4ea4dc441c0e7e6b5007abcc2da463bcb
93 lines
3.4 KiB
C
93 lines
3.4 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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* $Id$
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*
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* Copyright (C) 2003 Jörg Hohensohn [IDC]Dragon
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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 2
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* of the License, or (at your option) any later version.
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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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/* Code copied from firmware_flash plugin. */
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#include "crc32.h"
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/* Tool function to calculate a CRC32 across some buffer */
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/* third argument is either 0xFFFFFFFF to start or value from last piece */
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uint32_t crc_32(const void *src, uint32_t len, uint32_t crc32)
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{
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const unsigned char *buf = (const unsigned char *)src;
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/* CCITT standard polynomial 0x04C11DB7 */
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static const unsigned crc32_lookup[16] =
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{ /* lookup table for 4 bits at a time is affordable */
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0x00000000, 0x04C11DB7, 0x09823B6E, 0x0D4326D9,
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0x130476DC, 0x17C56B6B, 0x1A864DB2, 0x1E475005,
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0x2608EDB8, 0x22C9F00F, 0x2F8AD6D6, 0x2B4BCB61,
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0x350C9B64, 0x31CD86D3, 0x3C8EA00A, 0x384FBDBD
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};
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unsigned char byte;
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uint32_t t;
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while (len--)
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{
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byte = *buf++; /* get one byte of data */
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/* upper nibble of our data */
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t = crc32 >> 28; /* extract the 4 most significant bits */
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t ^= byte >> 4; /* XOR in 4 bits of data into the extracted bits */
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crc32 <<= 4; /* shift the CRC register left 4 bits */
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crc32 ^= crc32_lookup[t]; /* do the table lookup and XOR the result */
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/* lower nibble of our data */
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t = crc32 >> 28; /* extract the 4 most significant bits */
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t ^= byte & 0x0F; /* XOR in 4 bits of data into the extracted bits */
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crc32 <<= 4; /* shift the CRC register left 4 bits */
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crc32 ^= crc32_lookup[t]; /* do the table lookup and XOR the result */
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}
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return crc32;
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}
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/* crc_32r (derived from tinf crc32 which was taken from zlib)
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* CRC32 algorithm taken from the zlib source, which is
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* Copyright (C) 1995-1998 Jean-loup Gailly and Mark Adler
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*/
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/* Tool function to calculate a CRC32 (reversed polynomial) across some buffer */
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/* third argument is either the starting value or value from last piece */
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uint32_t crc_32r(const void *src, uint32_t len, uint32_t crc32)
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{
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const unsigned char* buf = src;
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/* reversed polynomial from other crc32 function -- 0xEDB88320 */
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static const unsigned crc32_lookup[16] =
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{
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0x00000000, 0x1DB71064, 0x3B6E20C8, 0x26D930AC,
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0x76DC4190, 0x6B6B51F4, 0x4DB26158, 0x5005713C,
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0xEDB88320, 0xF00F9344, 0xD6D6A3E8, 0xCB61B38C,
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0x9B64C2B0, 0x86D3D2D4, 0xA00AE278, 0xBDBDF21C
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};
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for(uint32_t i = 0; i < len; i++)
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{
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crc32 ^= buf[i];
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crc32 = crc32_lookup[crc32 & 0x0F] ^ (crc32 >> 4);
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crc32 = crc32_lookup[crc32 & 0x0F] ^ (crc32 >> 4);
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}
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return crc32;
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}
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