gr-satnogs/lib/libfec/viterbi615_port.c

/* K=15 r=1/6 Viterbi decoder in portable C
 * Copyright Mar 2004, Phil Karn, KA9Q
 * May be used under the terms of the GNU Lesser General Public License (LGPL)
 */
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <limits.h>
#include "fec.h"

typedef union {
  unsigned long w[512];
  unsigned char c[2048];
} decision_t;
typedef union {
  unsigned long w[16384];
} metric_t;

static union branchtab615 {
  unsigned long w[8192];
} Branchtab615[6] __attribute__((aligned(16)));
static int Init = 0;

/* State info for instance of Viterbi decoder */
struct v615 {
  metric_t metrics1; /* path metric buffer 1 */
  metric_t metrics2; /* path metric buffer 2 */
  decision_t *dp;          /* Pointer to current decision */
  metric_t *old_metrics,
           *new_metrics; /* Pointers to path metrics, swapped on every bit */
  decision_t *decisions;   /* Beginning of decisions for block */
};

/* Create a new instance of a Viterbi decoder */
void *create_viterbi615_port(int len)
{
  struct v615 *vp;

  if (!Init) {
    int polys[6] = { V615POLYA, V615POLYB, V615POLYC, V615POLYD, V615POLYE, V615POLYF };
    set_viterbi615_polynomial_port(polys);
  }
  if ((vp = (struct v615 *)malloc(sizeof(struct v615))) == NULL) {
    return NULL;
  }
  if ((vp->decisions = malloc((len + 14) * sizeof(decision_t))) == NULL) {
    free(vp);
    return NULL;
  }
  init_viterbi615(vp, 0);
  return vp;
}

void set_viterbi615_polynomial_port(int polys[6])
{
  int state;
  int i;

  for (state = 0; state < 8192; state++) {
    for (i = 0; i < 6; i++) {
      Branchtab615[i].w[state] = (polys[i] < 0) ^ parity((2 * state) & abs(
                                   polys[i])) ? 255 : 0;
    }
  }
  Init++;
}

/* Initialize Viterbi decoder for start of new frame */
int init_viterbi615_port(void *p, int starting_state)
{
  struct v615 *vp = p;
  int i;

  if (p == NULL) {
    return -1;
  }
  for (i = 0; i < 16384; i++) {
    vp->metrics1.w[i] = 1000;
  }

  vp->old_metrics = &vp->metrics1;
  vp->new_metrics = &vp->metrics2;
  vp->dp = vp->decisions;
  vp->old_metrics->w[starting_state & 16383] = 0; /* Bias known start state */
  return 0;
}

/* Viterbi chainback */
int chainback_viterbi615_port(
  void *p,
  unsigned char *data, /* Decoded output data */
  unsigned int nbits, /* Number of data bits */
  unsigned int endstate)  /* Terminal encoder state */
{
  struct v615 *vp = p;
  decision_t *d;

  if (p == NULL) {
    return -1;
  }
  d = (decision_t *)vp->decisions;
  endstate %= 16384;

  /* The store into data[] only needs to be done every 8 bits.
   * But this avoids a conditional branch, and the writes will
   * combine in the cache anyway
   */
  d += 14; /* Look past tail */
  while (nbits-- != 0) {
    int k;

    k = (d[nbits].c[endstate / 8] >> (endstate % 8)) & 1;
    endstate = (k << 13) | (endstate >> 1);
    data[nbits >> 3] = endstate >> 6;
  }
  return 0;
}

/* Delete instance of a Viterbi decoder */
void delete_viterbi615_port(void *p)
{
  struct v615 *vp = p;

  if (vp != NULL) {
    free(vp->decisions);
    free(vp);
  }
}

/* C-language butterfly */
#define BFLY(i) {\
unsigned long metric,m0,m1,m2,m3,decision0,decision1;\
    metric = ((Branchtab615[0].w[i] ^ syms[0]) + (Branchtab615[1].w[i] ^ syms[1])\
        +(Branchtab615[2].w[i] ^ syms[2]) + (Branchtab615[3].w[i] ^ syms[3])\
        +(Branchtab615[4].w[i] ^ syms[4]) + (Branchtab615[5].w[i] ^ syms[5]));\
    m0 = vp->old_metrics->w[i] + metric;\
    m1 = vp->old_metrics->w[i+8192] + (1530 - metric);\
    m2 = vp->old_metrics->w[i] + (1530-metric);\
    m3 = vp->old_metrics->w[i+8192] + metric;\
    decision0 = (signed long)(m0-m1) >= 0;\
    decision1 = (signed long)(m2-m3) >= 0;\
    vp->new_metrics->w[2*i] = decision0 ? m1 : m0;\
    vp->new_metrics->w[2*i+1] = decision1 ? m3 : m2;\
    d->c[i/4] |= ((decision0|(decision1<<1)) << ((2*i)&7));\
}
/* Update decoder with a block of demodulated symbols
 * Note that nbits is the number of decoded data bits, not the number
 * of symbols!
 */

int update_viterbi615_blk_port(void *p, unsigned char *syms, int nbits)
{
  struct v615 *vp = p;
  void *tmp;
  decision_t *d;
  int i;

  if (p == NULL) {
    return -1;
  }
  d = (decision_t *)vp->dp;
  while (nbits--) {
    memset(d, 0, sizeof(decision_t));
    for (i = 0; i < 8192; i++) {
      BFLY(i);
    }

    syms += 6;
    d++;
    /* Swap pointers to old and new metrics */
    tmp = vp->old_metrics;
    vp->old_metrics = vp->new_metrics;
    vp->new_metrics = tmp;
  }
  vp->dp = d;
  return 0;
}