99 lines
2.0 KiB
C
99 lines
2.0 KiB
C
/* Copyright (C) 2012 Connor Olding
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*
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* This program is licensed under the terms of the MIT License, and
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* is distributed without any warranty. You should have received a
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* copy of the license along with this program; see the file LICENSE.
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*/
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#include <stdlib.h>
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typedef unsigned long ulong;
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#include "crc32.h"
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int crc_big_endian = 0;
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ulong crc_polynomial = 0x04C11DB7;
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enum {
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TABLE_SIZE = 0x100
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};
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static ulong crc_be_table[TABLE_SIZE]; /* big endian */
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static ulong crc_le_table[TABLE_SIZE]; /* little endian */
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ulong crc_reflect(ulong input)
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{
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ulong reflected = 0;
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int i;
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for (i = 0; i < 4 * 8; i++) {
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reflected <<= 1;
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reflected |= input & 1;
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input >>= 1;
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}
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return reflected;
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}
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static void crc_fill_big_endian_table()
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{
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const ulong lsb = 1 << 31; /* least significant bit */
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ulong c;
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int i;
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for (c = 0; c < TABLE_SIZE; c++) {
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crc_be_table[c] = c << 24;
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for (i = 0; i < 8; i++) {
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if (crc_be_table[c] & lsb) {
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crc_be_table[c] <<= 1;
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crc_be_table[c] ^= crc_polynomial;
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} else {
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crc_be_table[c] <<= 1;
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}
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crc_be_table[c] &= 0xFFFFFFFF;
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}
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}
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}
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static void crc_fill_little_endian_table()
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{
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const ulong lsb = 1; /* least significant bit */
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const ulong reflected = crc_reflect(crc_polynomial);
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ulong c;
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int i;
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for (c = 0; c < TABLE_SIZE; c++) {
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crc_le_table[c] = c;
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for (i = 0; i < 8; i++) {
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if (crc_le_table[c] & lsb) {
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crc_le_table[c] >>= 1;
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crc_le_table[c] ^= reflected;
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} else {
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crc_le_table[c] >>= 1;
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}
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}
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}
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}
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static void crc_fill_tables_once()
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{
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static char filled = 0;
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if (crc_big_endian && !(filled & 1)) {
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crc_fill_big_endian_table();
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filled |= 1;
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} else if (!crc_big_endian && !(filled & 2)) {
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crc_fill_little_endian_table();
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filled |= 2;
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}
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}
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void crc_cycle(ulong *remainder, char c)
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{
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crc_fill_tables_once();
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if (crc_big_endian) {
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const ulong byte = crc_be_table[((*remainder) >> 24) ^ c];
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*remainder = ((*remainder) << 8) ^ byte;
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*remainder &= 0xFFFFFFFF;
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} else {
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const ulong byte = crc_le_table[((*remainder) ^ c) & 0xFF];
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*remainder = ((*remainder) >> 8) ^ byte;
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}
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}
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