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/*
* crcXXgen.c
*
* Generic CRC routines (for max XX bits poly)
*
* Copyright (C) 2011 Sylvain Munaut <tnt@246tNt.com>
*
* All Rights Reserved
*
* 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 2 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, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
/*! \addtogroup crcgen
* @{
*/
/*! \file crcXXgen.c
* \file Osmocom generic CRC routines (for max XX bits poly)
*/
#include <stdint.h>
#include <osmocom/core/bits.h>
#include <osmocom/core/crcXXgen.h>
/*! \brief Compute the CRC value of a given array of hard-bits
* \param[in] code The CRC code description to apply
* \param[in] in Array of hard bits
* \param[in] len Length of the array of hard bits
* \returns The CRC value
*/
uintXX_t
osmo_crcXXgen_compute_bits(const struct osmo_crcXXgen_code *code,
const ubit_t *in, int len)
{
const uintXX_t poly = code->poly;
uintXX_t crc = code->init;
int i, n = code->bits-1;
for (i=0; i<len; i++) {
uintXX_t bit = in[i] & 1;
crc ^= (bit << n);
if (crc & (1 << n)) {
crc <<= 1;
crc ^= poly;
} else {
crc <<= 1;
}
crc &= (1ULL << code->bits) - 1;
}
crc ^= code->remainder;
return crc;
}
/*! \brief Checks the CRC value of a given array of hard-bits
* \param[in] code The CRC code description to apply
* \param[in] in Array of hard bits
* \param[in] len Length of the array of hard bits
* \param[in] crc_bits Array of hard bits with the alleged CRC
* \returns 0 if CRC matches. 1 in case of error.
*
* The crc_bits array must have a length of code->len
*/
int
osmo_crcXXgen_check_bits(const struct osmo_crcXXgen_code *code,
const ubit_t *in, int len, const ubit_t *crc_bits)
{
uintXX_t crc;
int i;
crc = osmo_crcXXgen_compute_bits(code, in, len);
for (i=0; i<code->bits; i++)
if (crc_bits[i] ^ ((crc >> (code->bits-i-1)) & 1))
return 1;
return 0;
}
/*! \brief Computes and writes the CRC value of a given array of bits
* \param[in] code The CRC code description to apply
* \param[in] in Array of hard bits
* \param[in] len Length of the array of hard bits
* \param[in] crc_bits Array of hard bits to write the computed CRC to
*
* The crc_bits array must have a length of code->len
*/
void
osmo_crcXXgen_set_bits(const struct osmo_crcXXgen_code *code,
const ubit_t *in, int len, ubit_t *crc_bits)
{
uintXX_t crc;
int i;
crc = osmo_crcXXgen_compute_bits(code, in, len);
for (i=0; i<code->bits; i++)
crc_bits[i] = ((crc >> (code->bits-i-1)) & 1);
}
/*! @} */
/* vim: set syntax=c: */
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