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/* GMR-1 scrambling */
/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 4.9 */
/* (C) 2011-2016 by 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 Affero 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*! \addtogroup scramb
* @{
*/
/*! \file l1/scramb.c
* \brief Osmocom GMR-1 scrambling implementation
*/
#include <stdint.h>
#include <osmocom/core/bits.h>
/*
* h(D) = 1 + D + D^15
* i(D) = 1 + D + D^3 + D^6 + D^8 + D^10 + D^11 + D^14
*/
#define GMR1_SCRAMBLE_REG_INIT 0x4d4b
static inline int
gmr1_scramble_reg_next(uint16_t *reg)
{
int b;
uint16_t reg_val;
reg_val = *reg;
b = ((reg_val >> 14) ^ reg_val) & 1;
*reg = (reg_val << 1) | b;
return b;
}
/*! \brief Scrambles/Unscrambles a softbit vector
* \param[out] out output sbit_t array
* \param[in] in input sbit_t array
* \param[in] len length of the array to convert
*
* The output array can be equal to the input array for in-place
* scrambling/unscrambling
*/
void
gmr1_scramble_sbit(sbit_t *out, const sbit_t *in, int len)
{
uint16_t r = GMR1_SCRAMBLE_REG_INIT;
int i;
for (i=0; i<len; i++) {
sbit_t v = in[i];
out[i] = gmr1_scramble_reg_next(&r) ? -v : v;
}
}
/*! \brief Scrambles/Unscrambles an unpacked hard bit vector
* \param[out] out output ubit_t array
* \param[in] in input ubit_t array
* \param[in] len length of the array to convert
*
* The output array can be equal to the input array for in-place
* scrambling/unscrambling
*/
void
gmr1_scramble_ubit(ubit_t *out, const ubit_t *in, int len)
{
uint16_t r = GMR1_SCRAMBLE_REG_INIT;
int i;
for (i=0; i<len; i++) {
ubit_t v = in[i];
out[i] = v ^ gmr1_scramble_reg_next(&r);
}
}
/*! @} */
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