212 lines
4.8 KiB
C
212 lines
4.8 KiB
C
/* K=7 r=1/2 Viterbi decoder in portable C
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* Copyright Feb 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 int w[64];
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} metric_t;
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typedef union {
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unsigned long w[2];
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} decision_t;
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static union branchtab27 {
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unsigned char c[32];
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} Branchtab27[2] __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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* Don't change this without also changing references in [mmx|sse|sse2]bfly29.s!
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*/
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struct v27 {
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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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/* Initialize Viterbi decoder for start of new frame */
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int init_viterbi27_port(void *p, int starting_state)
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{
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struct v27 *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 < 64; i++) {
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vp->metrics1.w[i] = 63;
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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 & 63] = 0; /* Bias known start state */
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return 0;
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}
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void set_viterbi27_polynomial_port(int polys[2])
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{
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int state;
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for (state = 0; state < 32; state++) {
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Branchtab27[0].c[state] = (polys[0] < 0) ^ parity((2 * state) & abs(
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polys[0])) ? 255 : 0;
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Branchtab27[1].c[state] = (polys[1] < 0) ^ parity((2 * state) & abs(
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polys[1])) ? 255 : 0;
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}
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Init++;
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}
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/* Create a new instance of a Viterbi decoder */
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void *create_viterbi27_port(int len)
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{
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struct v27 *vp;
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if (!Init) {
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int polys[2] = { V27POLYA, V27POLYB };
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set_viterbi27_polynomial_port(polys);
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}
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if ((vp = malloc(sizeof(struct v27))) == NULL) {
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return NULL;
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}
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if ((vp->decisions = malloc((len + 6) * 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_viterbi27_port(vp, 0);
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return vp;
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}
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/* Viterbi chainback */
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int chainback_viterbi27_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 v27 *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 = vp->decisions;
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/* Make room beyond the end of the encoder register so we can
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* accumulate a full byte of decoded data
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*/
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endstate %= 64;
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endstate <<= 2;
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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 += 6; /* Look past tail */
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while (nbits-- != 0) {
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int k;
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k = (d[nbits].w[(endstate >> 2) / 32] >> ((endstate >> 2) % 32)) & 1;
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data[nbits >> 3] = endstate = (endstate >> 1) | (k << 7);
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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_viterbi27_port(void *p)
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{
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struct v27 *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 int metric,m0,m1,decision;\
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metric = (Branchtab27[0].c[i] ^ sym0) + (Branchtab27[1].c[i] ^ sym1);\
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m0 = vp->old_metrics->w[i] + metric;\
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m1 = vp->old_metrics->w[i+32] + (510 - metric);\
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decision = (signed int)(m0-m1) > 0;\
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vp->new_metrics->w[2*i] = decision ? m1 : m0;\
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d->w[i/16] |= decision << ((2*i)&31);\
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m0 -= (metric+metric-510);\
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m1 += (metric+metric-510);\
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decision = (signed int)(m0-m1) > 0;\
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vp->new_metrics->w[2*i+1] = decision ? m1 : m0;\
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d->w[i/16] |= decision << ((2*i+1)&31);\
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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_viterbi27_blk_port(void *p, unsigned char *syms, int nbits)
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{
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struct v27 *vp = p;
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void *tmp;
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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->dp;
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while (nbits--) {
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unsigned char sym0, sym1;
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d->w[0] = d->w[1] = 0;
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sym0 = *syms++;
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sym1 = *syms++;
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BFLY(0);
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BFLY(1);
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BFLY(2);
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BFLY(3);
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BFLY(4);
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BFLY(5);
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BFLY(6);
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BFLY(7);
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BFLY(8);
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BFLY(9);
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BFLY(10);
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BFLY(11);
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BFLY(12);
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BFLY(13);
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BFLY(14);
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BFLY(15);
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BFLY(16);
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BFLY(17);
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BFLY(18);
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BFLY(19);
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BFLY(20);
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BFLY(21);
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BFLY(22);
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BFLY(23);
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BFLY(24);
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BFLY(25);
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BFLY(26);
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BFLY(27);
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BFLY(28);
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BFLY(29);
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BFLY(30);
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BFLY(31);
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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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