2acc0ac542
later. We still need to hunt down snippets used that are not. 1324 modified files... http://www.rockbox.org/mail/archive/rockbox-dev-archive-2008-06/0060.shtml git-svn-id: svn://svn.rockbox.org/rockbox/trunk@17847 a1c6a512-1295-4272-9138-f99709370657
158 lines
4 KiB
C
158 lines
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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* Telechips firmware checksum support for scramble
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*
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* Copyright (C) 2007 Dave Chapman
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*
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* Thanks to Hein-Pieter van Braam for his work in identifying the
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* CRC algorithm used.
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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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#include <stdio.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <stdint.h>
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#include <stdlib.h>
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static uint32_t crctable[256];
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/* Simple implementation of a function to reverse the bottom n bits in x */
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static uint32_t bitreverse(uint32_t x,int n)
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{
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int i;
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uint32_t mask = 1<<(n-1);
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uint32_t res = 0;
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for (i=0; i<n; i++)
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{
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if (x & 1)
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res |= mask;
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x >>= 1;
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mask >>= 1;
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}
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return res;
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}
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/* Generate a lookup table for a reverse CRC32 */
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static void gentable(uint32_t poly)
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{
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int i;
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uint32_t r;
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uint32_t index;
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for (index = 0; index < 256; index++)
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{
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r = bitreverse(index,8) << 24;
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for (i=0; i<8; i++)
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{
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if (r & (1 << 31))
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r = (r << 1) ^ poly;
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else
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r<<=1;
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}
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crctable[index] = bitreverse(r,32);
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}
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}
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/* Perform a reverse CRC32 */
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static uint32_t calc_crc(unsigned char *message, int size)
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{
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uint32_t crc = 0;
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int i;
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for (i=0; i < size; i++){
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if ((i < 0x10) || (i >= 0x18)) {
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crc = crctable[((crc ^ (message[i])) & 0xff)] ^ (crc >> 8);
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}
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}
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return crc;
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}
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/* Endian-safe functions to read/write a 32-bit little-endian integer */
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static uint32_t get_uint32le(unsigned char* p)
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{
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return p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24);
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}
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static void put_uint32le(unsigned char* p, uint32_t x)
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{
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p[0] = x & 0xff;
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p[1] = (x >> 8) & 0xff;
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p[2] = (x >> 16) & 0xff;
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p[3] = (x >> 24) & 0xff;
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}
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/* A simple checksum - seems to be used by the TCC76x firmwares */
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void telechips_encode_sum(unsigned char* buf, int length)
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{
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uint32_t sum;
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int i;
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/* Set checksum field to 0 */
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put_uint32le(buf + 0x10, 0);
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/* Perform a simple sum, treating the file as a series of 32-bit
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little-endian integers */
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sum = 0;
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for (i=0; i < length; i+=4) {
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sum += get_uint32le(buf + i);
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}
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/* Negate the sum - this means that the sum of the whole file
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(including this value) will be equal to zero */
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sum = -sum;
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/* Set the checksum field */
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put_uint32le(buf + 0x10, sum);
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}
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/* Two reverse CRC32 checksums - seems to be used by the TCC77x firmwares */
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void telechips_encode_crc(unsigned char* buf, int length)
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{
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uint32_t crc1,crc2;
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/* Generate the CRC table */
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gentable(0x8001801BL);
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/* Clear the existing CRC values */
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put_uint32le(buf+0x10, 0);
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put_uint32le(buf+0x18, 0);
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/* Write the length */
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put_uint32le(buf+0x1c, length);
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/* Calculate the first CRC - over the entire file */
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crc1 = calc_crc(buf, length);
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/* What happens next depends on the filesize */
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if (length >= 128*1024)
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{
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put_uint32le(buf+0x18, crc1);
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crc2 = calc_crc(buf, 128*1024);
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put_uint32le(buf+0x10, crc2);
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} else {
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put_uint32le(buf+0x10, crc1);
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}
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}
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