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/**
* Flake: FLAC audio encoder
* Copyright (c) 2006 Justin Ruggles
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "common.h"
#include "crc.h"
static void
crc_init_table(uint16_t *table, int bits, int poly)
{
int i, j, crc;
poly = (poly + (1<<bits));
for(i=0; i<256; i++) {
crc = i;
for(j=0; j<bits; j++) {
if(crc & (1<<(bits-1))) {
crc = (crc << 1) ^ poly;
} else {
crc <<= 1;
}
}
table[i] = (crc & ((1<<bits)-1));
}
}
/* CRC key for polynomial, x^8 + x^2 + x^1 + 1 */
#define CRC8_POLY 0x07
/* CRC key for polynomial, x^16 + x^15 + x^2 + 1 */
#define CRC16_POLY 0x8005
static uint16_t crc8tab[256];
static uint16_t crc16tab[256];
void
crc_init()
{
crc_init_table(crc8tab, 8, CRC8_POLY);
crc_init_table(crc16tab, 16, CRC16_POLY);
}
static uint16_t
calc_crc(const uint16_t *table, int bits, const uint8_t *data, uint32_t len)
{
uint16_t crc, v1, v2;
crc = 0;
while(len--) {
v1 = (crc << 8) & ((1 << bits) - 1);
v2 = (crc >> (bits - 8)) ^ *data++;
assert(v2 < 256);
crc = v1 ^ table[v2];
}
return crc;
}
uint8_t
calc_crc8(const uint8_t *data, uint32_t len)
{
uint8_t crc;
if(data == NULL) return 0;
crc = calc_crc(crc8tab, 8, data, len);
return crc;
}
uint16_t
calc_crc16(const uint8_t *data, uint32_t len)
{
uint16_t crc;
if(data == NULL) return 0;
crc = calc_crc(crc16tab, 16, data, len);
return crc;
}
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