179 lines
4.4 KiB
C
179 lines
4.4 KiB
C
/* K=15 r=1/6 Viterbi decoder in portable C
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* Copyright Mar 2004, Phil Karn, KA9Q
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* May be used under the terms of the GNU Lesser General Public License (LGPL)
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <memory.h>
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#include <limits.h>
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#include "fec.h"
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typedef union {
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unsigned long w[512];
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unsigned char c[2048];
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} decision_t;
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typedef union {
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unsigned long w[16384];
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} metric_t;
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static union branchtab615 {
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unsigned long w[8192];
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} Branchtab615[6] __attribute__((aligned(16)));
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static int Init = 0;
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/* State info for instance of Viterbi decoder */
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struct v615 {
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metric_t metrics1; /* path metric buffer 1 */
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metric_t metrics2; /* path metric buffer 2 */
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decision_t *dp; /* Pointer to current decision */
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metric_t *old_metrics,
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*new_metrics; /* Pointers to path metrics, swapped on every bit */
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decision_t *decisions; /* Beginning of decisions for block */
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};
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/* Create a new instance of a Viterbi decoder */
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void *create_viterbi615_port(int len)
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{
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struct v615 *vp;
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if (!Init) {
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int polys[6] = { V615POLYA, V615POLYB, V615POLYC, V615POLYD, V615POLYE, V615POLYF };
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set_viterbi615_polynomial_port(polys);
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}
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if ((vp = (struct v615 *)malloc(sizeof(struct v615))) == NULL) {
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return NULL;
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}
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if ((vp->decisions = malloc((len + 14) * sizeof(decision_t))) == NULL) {
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free(vp);
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return NULL;
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}
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init_viterbi615(vp, 0);
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return vp;
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}
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void set_viterbi615_polynomial_port(int polys[6])
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{
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int state;
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int i;
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for (state = 0; state < 8192; state++) {
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for (i = 0; i < 6; i++) {
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Branchtab615[i].w[state] = (polys[i] < 0) ^ parity((2 * state) & abs(
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polys[i])) ? 255 : 0;
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}
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}
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Init++;
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}
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/* Initialize Viterbi decoder for start of new frame */
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int init_viterbi615_port(void *p, int starting_state)
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{
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struct v615 *vp = p;
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int i;
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if (p == NULL) {
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return -1;
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}
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for (i = 0; i < 16384; i++) {
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vp->metrics1.w[i] = 1000;
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}
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vp->old_metrics = &vp->metrics1;
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vp->new_metrics = &vp->metrics2;
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vp->dp = vp->decisions;
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vp->old_metrics->w[starting_state & 16383] = 0; /* Bias known start state */
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return 0;
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}
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/* Viterbi chainback */
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int chainback_viterbi615_port(
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void *p,
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unsigned char *data, /* Decoded output data */
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unsigned int nbits, /* Number of data bits */
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unsigned int endstate) /* Terminal encoder state */
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{
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struct v615 *vp = p;
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decision_t *d;
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if (p == NULL) {
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return -1;
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}
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d = (decision_t *)vp->decisions;
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endstate %= 16384;
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/* The store into data[] only needs to be done every 8 bits.
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* But this avoids a conditional branch, and the writes will
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* combine in the cache anyway
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*/
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d += 14; /* Look past tail */
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while (nbits-- != 0) {
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int k;
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k = (d[nbits].c[endstate / 8] >> (endstate % 8)) & 1;
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endstate = (k << 13) | (endstate >> 1);
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data[nbits >> 3] = endstate >> 6;
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}
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return 0;
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}
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/* Delete instance of a Viterbi decoder */
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void delete_viterbi615_port(void *p)
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{
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struct v615 *vp = p;
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if (vp != NULL) {
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free(vp->decisions);
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free(vp);
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}
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}
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/* C-language butterfly */
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#define BFLY(i) {\
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unsigned long metric,m0,m1,m2,m3,decision0,decision1;\
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metric = ((Branchtab615[0].w[i] ^ syms[0]) + (Branchtab615[1].w[i] ^ syms[1])\
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+(Branchtab615[2].w[i] ^ syms[2]) + (Branchtab615[3].w[i] ^ syms[3])\
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+(Branchtab615[4].w[i] ^ syms[4]) + (Branchtab615[5].w[i] ^ syms[5]));\
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m0 = vp->old_metrics->w[i] + metric;\
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m1 = vp->old_metrics->w[i+8192] + (1530 - metric);\
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m2 = vp->old_metrics->w[i] + (1530-metric);\
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m3 = vp->old_metrics->w[i+8192] + metric;\
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decision0 = (signed long)(m0-m1) >= 0;\
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decision1 = (signed long)(m2-m3) >= 0;\
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vp->new_metrics->w[2*i] = decision0 ? m1 : m0;\
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vp->new_metrics->w[2*i+1] = decision1 ? m3 : m2;\
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d->c[i/4] |= ((decision0|(decision1<<1)) << ((2*i)&7));\
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}
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/* Update decoder with a block of demodulated symbols
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* Note that nbits is the number of decoded data bits, not the number
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* of symbols!
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*/
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int update_viterbi615_blk_port(void *p, unsigned char *syms, int nbits)
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{
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struct v615 *vp = p;
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void *tmp;
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decision_t *d;
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int i;
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if (p == NULL) {
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return -1;
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}
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d = (decision_t *)vp->dp;
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while (nbits--) {
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memset(d, 0, sizeof(decision_t));
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for (i = 0; i < 8192; i++) {
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BFLY(i);
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}
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syms += 6;
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d++;
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/* Swap pointers to old and new metrics */
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tmp = vp->old_metrics;
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vp->old_metrics = vp->new_metrics;
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vp->new_metrics = tmp;
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}
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vp->dp = d;
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return 0;
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}
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