96 lines
2.3 KiB
C
96 lines
2.3 KiB
C
/* GMR-1 scrambling */
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/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 4.9 */
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/* (C) 2011-2019 by Sylvain Munaut <tnt@246tNt.com>
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* All Rights Reserved
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*! \addtogroup scramb
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* @{
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*/
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/*! \file l1/scramb.c
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* \brief Osmocom GMR-1 scrambling implementation
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*/
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#include <stdint.h>
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#include <osmocom/core/bits.h>
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/*
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* h(D) = 1 + D + D^15
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* i(D) = 1 + D + D^3 + D^6 + D^8 + D^10 + D^11 + D^14
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*/
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#define GMR1_SCRAMBLE_REG_INIT 0x4d4b
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static inline int
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gmr1_scramble_reg_next(uint16_t *reg)
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{
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int b;
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uint16_t reg_val;
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reg_val = *reg;
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b = ((reg_val >> 14) ^ reg_val) & 1;
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*reg = (reg_val << 1) | b;
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return b;
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}
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/*! \brief Scrambles/Unscrambles a softbit vector
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* \param[out] out output sbit_t array
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* \param[in] in input sbit_t array
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* \param[in] len length of the array to convert
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*
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* The output array can be equal to the input array for in-place
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* scrambling/unscrambling
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*/
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void
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gmr1_scramble_sbit(sbit_t *out, const sbit_t *in, int len)
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{
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uint16_t r = GMR1_SCRAMBLE_REG_INIT;
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int i;
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for (i=0; i<len; i++) {
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sbit_t v = in[i];
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out[i] = gmr1_scramble_reg_next(&r) ? -v : v;
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}
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}
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/*! \brief Scrambles/Unscrambles an unpacked hard bit vector
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* \param[out] out output ubit_t array
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* \param[in] in input ubit_t array
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* \param[in] len length of the array to convert
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*
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* The output array can be equal to the input array for in-place
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* scrambling/unscrambling
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*/
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void
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gmr1_scramble_ubit(ubit_t *out, const ubit_t *in, int len)
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{
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uint16_t r = GMR1_SCRAMBLE_REG_INIT;
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int i;
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for (i=0; i<len; i++) {
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ubit_t v = in[i];
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out[i] = v ^ gmr1_scramble_reg_next(&r);
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}
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}
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/*! @} */
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