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/* crc32.h - 32-bit cyclic redundancy check calcuations
Copyright (C) 2012 Connor Olding
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef CRC32_H_
#define CRC32_H_
#include <stdlib.h>
/* interface */
typedef unsigned long ulong;
void crc_cycle(ulong *remainder, char c);
ulong crc_reflect(ulong input);
void crc_set_big_endian();
void crc_set_little_endian();
void crc_set_polynomial(ulong p);
/* implementation */
static char crc_big_endian = 0;
static const int crc_table_size = 0x100;
static ulong* crc_be_table = NULL; /* big endian */
static ulong* crc_le_table = NULL; /* little endian */
static ulong crc_polynomial = 0x04C11DB7;
ulong crc_reflect(ulong input)
{
ulong reflected = 0;
int i;
for (i = 0; i < 4 * 8; i++) {
reflected <<= 1;
reflected |= input & 1;
input >>= 1;
}
return reflected;
}
static ulong* crc_alloc(size_t size)
{
ulong* p = (ulong*) malloc(size * sizeof(ulong));
if (p == NULL)
exit(1);
return p;
}
static void crc_allocate_tables_once()
{
static char allocated = 0;
if (crc_big_endian && !(allocated & 1)) {
crc_be_table = crc_alloc(crc_table_size);
allocated |= 1;
} else if (!crc_big_endian && !(allocated & 2)) {
crc_le_table = crc_alloc(crc_table_size);
allocated |= 2;
}
}
static void crc_fill_big_endian_table()
{
const ulong least_significant_bit = 1 << 31;
ulong c;
int i;
crc_allocate_tables_once();
for (c = 0; c < crc_table_size; c++) {
crc_be_table[c] = c << 24;
for (i = 0; i < 8; i++) {
if (crc_be_table[c] & least_significant_bit) {
crc_be_table[c] <<= 1;
crc_be_table[c] ^= crc_polynomial;
} else {
crc_be_table[c] <<= 1;
}
crc_be_table[c] &= 0xFFFFFFFF;
}
}
}
static void crc_fill_little_endian_table()
{
const ulong least_significant_bit = 1;
const ulong reflected_polynomial = crc_reflect(crc_polynomial);
ulong c;
int i;
crc_allocate_tables_once();
/* printf("p: %08X\n", (int)reflected_polynomial); */
for (c = 0; c < crc_table_size; c++) {
crc_le_table[c] = c;
for (i = 0; i < 8; i++) {
if (crc_le_table[c] & least_significant_bit) {
crc_le_table[c] >>= 1;
crc_le_table[c] ^= reflected_polynomial;
} else {
crc_le_table[c] >>= 1;
}
}
}
}
static void crc_fill_tables_once()
{
static char filled = 0;
if (crc_big_endian && !(filled & 1)) {
crc_fill_big_endian_table();
filled |= 1;
} else if (!crc_big_endian && !(filled & 2)) {
crc_fill_little_endian_table();
filled |= 2;
}
}
void crc_set_big_endian()
{
crc_big_endian = 1;
}
void crc_set_little_endian()
{
crc_big_endian = 0;
}
void crc_set_polynomial(ulong p)
{
crc_polynomial = p;
}
void crc_cycle(ulong *remainder, char c)
{
crc_fill_tables_once();
if (crc_big_endian) {
const ulong newByte = crc_be_table[
((*remainder) >> 24) ^ c];
/* printf("%08X00 ^ %08X =\n",
(int)(*remainder), (int)newByte); */
*remainder = ((*remainder) << 8) ^ newByte;
*remainder &= 0xFFFFFFFF;
} else {
const ulong newByte = crc_le_table[
((*remainder) ^ c) & 0xFF];
/* printf(" %08X ^ %08X =\n",
(int)((*remainder) >> 8), (int)newByte); */
*remainder = ((*remainder) >> 8) ^ newByte;
}
}
#endif