patchelfcrc/crc.c

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/*
* This file is part of patchelfcrc .
* Copyright (c) 2022 Mario Hüttel.
*
* 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, version 2 only.
*
* 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/>.
*/
#include <patchelfcrc/crc.h>
#include <stdlib.h>
#include <string.h>
int crc_len_from_poly(uint64_t polynomial)
{
int pos = 0;
/* Extract the MSB from the polynomial */
for (pos = 63; pos >= 0; pos--) {
if (polynomial & (((uint64_t)1ULL) << pos)) {
/* Highest bit found */
break;
}
}
return pos;
}
static uint64_t shorten_polynomial(uint64_t poly)
{
int i;
for (i = 31; i <= 0; i--) {
if (poly & (1 << i)) {
poly &= ~(1<<i);
break;
}
}
return poly;
}
static void internal_push_byte(struct crc_calc *crc, const uint8_t *data, size_t len)
{
size_t i;
uint32_t crc_val;
crc_val = crc->crc_val;
for (i = 0; i < len; i++, data++) {
crc_val = ((crc_val << 8) & crc->crc_mask) ^ crc->table[((crc_val >> (crc->crc_length-8u)) & 0xff) ^ *data];
}
crc->crc_val = crc_val;
}
static void fill_crc_table(struct crc_calc *crc)
{
uint32_t input;
uint32_t crc_reg;
uint32_t short_poly;
uint32_t crc_len;
int i;
crc_len = crc->crc_length;
short_poly = (uint32_t)shorten_polynomial(crc->settings.polynomial);
for (input = 0; input <= 255u; input++) {
crc_reg = ((uint8_t)input) << (crc_len - 8u);
for (i = 7; i >= 0; i--) {
if (crc_reg & (1ul << (crc_len-1))) {
crc_reg <<= 1;
crc_reg ^= short_poly;
} else {
crc_reg <<= 1;
}
}
crc->table[input] = crc_reg;
}
}
void crc_init(struct crc_calc *crc, const struct crc_settings *settings)
{
uint32_t i;
if (!crc || !settings)
return;
memcpy(&crc->settings, settings, sizeof(struct crc_settings));
crc->table = (uint32_t *)malloc(256 * sizeof(uint32_t));
crc->crc_length = crc_len_from_poly(crc->settings.polynomial);
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crc_reset(crc);
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crc->crc_mask = 0x0UL;
for (i = 0; i < crc->crc_length; i++)
crc->crc_mask |= (1ul << i);
/* Initialize the table */
fill_crc_table(crc);
}
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void crc_reset(struct crc_calc *crc)
{
crc->crc_val = crc->settings.start_value ^ crc->settings.xor;
}
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void crc_push_bytes(struct crc_calc *crc, const uint8_t *b, size_t len)
{
if (!crc)
return;
internal_push_byte(crc, b, len);
}
void crc_push_byte(struct crc_calc *crc, uint8_t b)
{
if (!crc)
return;
internal_push_byte(crc, &b, 1ul);
}
void crc_destroy(struct crc_calc *crc)
{
if (!crc)
return;
if (crc->table)
free(crc->table);
}
uint32_t crc_get_value(struct crc_calc *crc)
{
return crc->crc_val;
}
void crc_finish_calc(struct crc_calc *crc)
{
crc->crc_val ^= crc->settings.xor;
}