mirror of https://gerrit.osmocom.org/osmo-tetra
97 lines
2.7 KiB
C
97 lines
2.7 KiB
C
/* Shortened (30,14) Reed-Muller (RM) code */
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/* (C) 2011 by Harald Welte <laforge@gnumonks.org>
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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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*/
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#include <stdint.h>
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#include <stdio.h>
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#include <lower_mac/tetra_rm3014.h>
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/* Generator matrix from Section 8.2.3.2 */
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static const uint8_t rm_30_14_gen[14][16] = {
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{ 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0 },
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{ 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0 },
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{ 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0 },
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{ 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0 },
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{ 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 1, 0 },
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{ 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0 },
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{ 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 1, 1, 0 },
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{ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1 },
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{ 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 1 },
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{ 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1 },
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{ 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1 },
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{ 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 1 },
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{ 0, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 1, 1 },
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{ 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1 }
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};
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static uint32_t rm_30_14_rows[14];
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static uint32_t shift_bits_together(const uint8_t *bits, int len)
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{
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uint32_t ret = 0;
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int i;
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for (i = len-1; i >= 0; i--)
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ret |= bits[i] << (len-1-i);
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return ret;
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}
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void tetra_rm3014_init(void)
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{
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int i;
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uint32_t val;
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for (i = 0; i < 14; i++) {
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/* upper 14 bits identity matrix */
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val = (1 << (16+13 - i));
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/* lower 16 bits from rm_30_14_gen */
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val |= shift_bits_together(rm_30_14_gen[i], 16);
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rm_30_14_rows[i] = val;
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printf("rm_30_14_rows[%u] = 0x%08x\n", i, val);
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}
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}
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uint32_t tetra_rm3014_compute(const uint16_t in)
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{
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int i;
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uint32_t val = 0;
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for (i = 0; i < 14; i++) {
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uint32_t bit = (in >> (14-1-i)) & 1;
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if (bit)
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val ^= rm_30_14_rows[i];
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/* we can skip the 'else' as XOR with 0 has no effect */
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}
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return val;
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}
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/**
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* This is a systematic code. We can remove the control bits
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* and then check for an error. Maybe correct it in the future.
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*/
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int tetra_rm3014_decode(const uint32_t inp, uint16_t *out)
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{
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*out = inp >> 16;
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return 0;
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}
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