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crc32
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refactored crc32.h

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pull/2/head
Connor Olding 11 years ago
parent 4f7b15f0f2
commit 29529cd8f2
4 changed files with 105 additions and 146 deletions
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2
Makefile
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@ -1,6 +1,6 @@
PROGRAM = crc32
.PHONY: all clean install
FILES = main.c args.c
FILES = main.c args.c crc32.c
CFLAGS += -Wall -Werror -ansi -pedantic
LDFLAGS +=

98
crc32.c
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@ -0,0 +1,98 @@
/* Copyright (C) 2012 Connor Olding
*
* This program is licensed under the terms of the MIT License, and
* is distributed without any warranty. You should have received a
* copy of the license along with this program; see the file LICENSE.
*/
#include <stdlib.h>
typedef unsigned long ulong;
#include "crc32.h"
int crc_big_endian = 0;
ulong crc_polynomial = 0x04C11DB7;
enum {
TABLE_SIZE = 0x100
};
static ulong crc_be_table[TABLE_SIZE]; /* big endian */
static ulong crc_le_table[TABLE_SIZE]; /* little endian */
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 void crc_fill_big_endian_table()
{
const ulong lsb = 1 << 31; /* least significant bit */
ulong c;
int i;
for (c = 0; c < TABLE_SIZE; c++) {
crc_be_table[c] = c << 24;
for (i = 0; i < 8; i++) {
if (crc_be_table[c] & lsb) {
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 lsb = 1; /* least significant bit */
const ulong reflected = crc_reflect(crc_polynomial);
ulong c;
int i;
for (c = 0; c < TABLE_SIZE; c++) {
crc_le_table[c] = c;
for (i = 0; i < 8; i++) {
if (crc_le_table[c] & lsb) {
crc_le_table[c] >>= 1;
crc_le_table[c] ^= reflected;
} 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_cycle(ulong *remainder, char c)
{
crc_fill_tables_once();
if (crc_big_endian) {
const ulong byte = crc_be_table[((*remainder) >> 24) ^ c];
*remainder = ((*remainder) << 8) ^ byte;
*remainder &= 0xFFFFFFFF;
} else {
const ulong byte = crc_le_table[((*remainder) ^ c) & 0xFF];
*remainder = ((*remainder) >> 8) ^ byte;
}
}

144
crc32.h
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@ -5,149 +5,9 @@
* copy of the license along with this program; see the file LICENSE.
*/
#ifndef CRC32_H_
#define CRC32_H_
#include <stdlib.h>
/* interface */
typedef unsigned long ulong;
int crc_big_endian;
ulong crc_polynomial;
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

7
main.c
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@ -9,6 +9,8 @@
#include <stdlib.h>
#include <string.h>
typedef unsigned long ulong;
#include "crc32.h"
#include "args.h"
@ -65,7 +67,7 @@ static void handle_flag(char flag, char *(*nextarg)())
printf(help2);
exit(0);
case 'e':
crc_set_big_endian();
crc_big_endian = 1;
return;
case 'b':
print_binary = 1;
@ -85,7 +87,7 @@ static void handle_flag(char flag, char *(*nextarg)())
break;
case 'p':
next = check_next(flag, nextarg());
crc_set_polynomial(strtoul(next, NULL, 0));
crc_polynomial = strtoul(next, NULL, 0);
break;
default:
fprintf(stderr, "Unknown flag: -%c\n", flag);
@ -147,7 +149,6 @@ static void print_crc(ulong remainder)
int main(int argc, char **argv)
{
string_node *n;
crc_set_little_endian();
args_parse(argc, argv, handle_flag, add_input);
if (!input_node) {

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