155 lines
3.2 KiB
C
155 lines
3.2 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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#ifndef CRC32_H_
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#define CRC32_H_
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#include <stdlib.h>
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/* interface */
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typedef unsigned long ulong;
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void crc_cycle(ulong *remainder, char c);
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ulong crc_reflect(ulong input);
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void crc_set_big_endian();
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void crc_set_little_endian();
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void crc_set_polynomial(ulong p);
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/* implementation */
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static char crc_big_endian = 0;
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static const int crc_table_size = 0x100;
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static ulong* crc_be_table = NULL; /* big endian */
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static ulong* crc_le_table = NULL; /* little endian */
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static ulong crc_polynomial = 0x04C11DB7;
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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 ulong* crc_alloc(size_t size)
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{
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ulong* p = (ulong*) malloc(size * sizeof(ulong));
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if (p == NULL)
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exit(1);
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return p;
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}
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static void crc_allocate_tables_once()
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{
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static char allocated = 0;
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if (crc_big_endian && !(allocated & 1)) {
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crc_be_table = crc_alloc(crc_table_size);
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allocated |= 1;
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} else if (!crc_big_endian && !(allocated & 2)) {
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crc_le_table = crc_alloc(crc_table_size);
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allocated |= 2;
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}
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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 least_significant_bit = 1 << 31;
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ulong c;
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int i;
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crc_allocate_tables_once();
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for (c = 0; c < crc_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] & least_significant_bit) {
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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 least_significant_bit = 1;
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const ulong reflected_polynomial = crc_reflect(crc_polynomial);
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ulong c;
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int i;
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crc_allocate_tables_once();
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/* printf("p: %08X\n", (int)reflected_polynomial); */
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for (c = 0; c < crc_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] & least_significant_bit) {
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crc_le_table[c] >>= 1;
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crc_le_table[c] ^= reflected_polynomial;
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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_set_big_endian()
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{
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crc_big_endian = 1;
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}
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void crc_set_little_endian()
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{
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crc_big_endian = 0;
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}
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void crc_set_polynomial(ulong p)
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{
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crc_polynomial = p;
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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 newByte = crc_be_table[
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((*remainder) >> 24) ^ c];
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/* printf("%08X00 ^ %08X =\n",
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(int)(*remainder), (int)newByte); */
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*remainder = ((*remainder) << 8) ^ newByte;
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*remainder &= 0xFFFFFFFF;
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} else {
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const ulong newByte = crc_le_table[
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((*remainder) ^ c) & 0xFF];
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/* printf(" %08X ^ %08X =\n",
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(int)((*remainder) >> 8), (int)newByte); */
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*remainder = ((*remainder) >> 8) ^ newByte;
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}
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}
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#endif
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