126 lines
3.2 KiB
C
126 lines
3.2 KiB
C
/*
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* Copyright (c) 2013, Ismael Gomez-Miguelez <gomezi@tcd.ie>.
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* This file is part of OSLD-lib (http://https://github.com/ismagom/osld-lib)
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*
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* OSLD-lib is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser 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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* OSLD-lib 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 Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with OSLD-lib. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**@TODO frontend to FEC library if installed
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <math.h>
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#include "fec/convcoder.h"
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#include "parity.h"
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#include "viterbi37.h"
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#define DEB 0
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int decode37(void *o, float *symbols, char *data) {
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viterbi_t *q = o;
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int i;
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int len = q->tail_biting ? q->framebits : (q->framebits + q->K - 1);
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float amp = 0;
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for (i=0;i<3*len;i++) {
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if (fabsf(symbols[i] > amp)) {
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amp = symbols[i];
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}
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}
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/* Decode it and make sure we get the right answer */
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/* Initialize Viterbi decoder */
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init_viterbi37_port(q->ptr, q->tail_biting?-1:0);
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/* Decode block */
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update_viterbi37_blk_port(q->ptr, symbols,q->framebits + q->K - 1, amp, len);
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/* Do Viterbi chainback */
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chainback_viterbi37_port(q->ptr, data, q->framebits, 0);
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return q->framebits;
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}
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void free37(void *o) {
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viterbi_t *q = o;
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delete_viterbi37_port(q->ptr);
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}
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int init37(viterbi_t *q, int poly[3], int framebits, bool tail_biting) {
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q->K = 7;
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q->R = 3;
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q->framebits = framebits;
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q->tail_biting = tail_biting;
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q->decode = decode37;
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q->free = free37;
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if ((q->ptr = create_viterbi37_port(poly, framebits, tail_biting)) == NULL) {
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fprintf(stderr, "create_viterbi37 failed\n");
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return -1;
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} else {
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return 0;
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}
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}
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int viterbi_init(viterbi_t *q, viterbi_type_t type, int poly[3], int framebits, bool tail_bitting) {
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switch(type) {
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case CONVCODER_37:
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return init37(q, poly, framebits, tail_bitting);
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default:
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fprintf(stderr, "Decoder not implemented\n");
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return -1;
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}
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}
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void viterbi_free(viterbi_t *q) {
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q->free(q);
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}
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/* symbols are real-valued */
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int viterbi_decode(viterbi_t *q, float *symbols, char *data) {
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return q->decode(q, symbols, data);
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}
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int conv_encode(convcoder_t *q, char *input, char *output) {
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unsigned int sr;
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int i,j;
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int len = q->tail_biting ? q->framelength : (q->framelength + q->K - 1);
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if (q->tail_biting) {
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sr = 0;
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for (i=q->framelength - q->K + 1; i<q->framelength; i++) {
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if (DEB) printf("%3d: sr=%3d, bit=%d\n",i,sr&7,input[i]);
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sr = (sr << 1) | (input[i] & 1);
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}
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} else {
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sr = 0;
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}
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if (DEB) printf("state st=%d\n",sr&7);
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for (i = 0; i < len; i++) {
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int bit = (i < q->framelength) ? (input[i] & 1) : 0;
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sr = (sr << 1) | bit;
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if (DEB) printf("%d, ",input[i]);
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for (j=0;j<q->R;j++) {
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output[q->R * i + j] = parity(sr & q->poly[j]);
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}
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}
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if (DEB) printf("\n");
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if (DEB) printf("state fin=%u\n",sr&7);
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return q->R*len;
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}
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