gr-satnogs/lib/libfec/viterbi29_av.c

/* K=9 r=1/2 Viterbi decoder for PowerPC G4/G5 Altivec
 * Copyright Feb 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 <sys/sysctl.h>
#include "fec.h"

typedef union {
  unsigned char c[256];
  vector bool char v[16];
} decision_t;
typedef union {
  unsigned char c[256];
  vector unsigned char v[16];
} metric_t;

static union branchtab29 {
  unsigned char c[128];
  vector unsigned char v[8];
} Branchtab29[2];
static int Init = 0;

/* State info for instance of Viterbi decoder */
struct v29 {
  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 */
};

/* Initialize Viterbi decoder for start of new frame */
int init_viterbi29_av(void *p, int starting_state)
{
  struct v29 *vp = p;
  int i;

  if (p == NULL) {
    return -1;
  }
  for (i = 0; i < 16; i++) {
    vp->metrics1.v[i] = (vector unsigned char)(63);
  }

  vp->old_metrics = &vp->metrics1;
  vp->new_metrics = &vp->metrics2;
  vp->dp = vp->decisions;
  vp->old_metrics->c[starting_state & 255] = 0; /* Bias known start state */
  return 0;
}

void set_viterbi29_polynomial_av(int polys[2])
{
  int state;

  for (state = 0; state < 128; state++) {
    Branchtab29[0].c[state] = (polys[0] < 0) ^ parity((2 * state) & abs(
                                polys[0])) ? 255 : 0;
    Branchtab29[1].c[state] = (polys[1] < 0) ^ parity((2 * state) & abs(
                                polys[1])) ? 255 : 0;
  }
  Init++;
}

/* Create a new instance of a Viterbi decoder */
void *create_viterbi29_av(int len)
{
  struct v29 *vp;

  if (!Init) {
    int polys[2] = { V29POLYA, V29POLYB };
    set_viterbi29_polynomial_av(polys);
  }
  if ((vp = (struct v29 *)malloc(sizeof(struct v29))) == NULL) {
    return NULL;
  }
  if ((vp->decisions = (decision_t *)malloc((len + 8) * sizeof(
                         decision_t))) == NULL) {
    free(vp);
    return NULL;
  }
  init_viterbi29_av(vp, 0);
  return vp;
}

/* Viterbi chainback */
int chainback_viterbi29_av(
  void *p,
  unsigned char *data, /* Decoded output data */
  unsigned int nbits, /* Number of data bits */
  unsigned int endstate)  /* Terminal encoder state */
{
  struct v29 *vp = p;
  decision_t *d;

  if (p == NULL) {
    return -1;
  }
  d = (decision_t *)vp->decisions;
  /* Make room beyond the end of the encoder register so we can
   * accumulate a full byte of decoded data
   */
  endstate %= 256;

  /* 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 += 8; /* Look past tail */
  while (nbits-- != 0) {
    int k;

    k = d[nbits].c[endstate] & 1;
    data[nbits >> 3] = endstate = (endstate >> 1) | (k << 7);
  }
  return 0;
}


/* Delete instance of a Viterbi decoder */
void delete_viterbi29_av(void *p)
{
  struct v29 *vp = p;

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


int update_viterbi29_blk_av(void *p, unsigned char *syms, int nbits)
{
  struct v29 *vp = p;
  decision_t *d;
  int i;

  if (p == NULL) {
    return -1;
  }
  d = (decision_t *)vp->dp;

  while (nbits--) {
    vector unsigned char sym1v, sym2v;
    void *tmp;

    /* All this seems necessary just to load a byte into all elements of a vector! */
    sym1v = vec_perm(vec_ld(0, syms), vec_ld(1, syms), vec_lvsl(0,
                     syms)); /* sym1v.0 = syms[0]; sym1v.1 = syms[1] */
    sym2v = vec_splat(sym1v, 1); /* Splat syms[1] across sym2v */
    sym1v = vec_splat(sym1v, 0); /* Splat syms[0] across sym1v */
    syms += 2;

    for (i = 0; i < 8; i++) {
      vector bool char decision0, decision1;
      vector unsigned char metric, m_metric, m0, m1, m2, m3, survivor0, survivor1;

      /* Form branch metrics */
      metric = vec_avg(vec_xor(Branchtab29[0].v[i], sym1v),
                       vec_xor(Branchtab29[1].v[i], sym2v));
      metric = vec_sr(metric, (vector unsigned char)(3));
      m_metric = (vector unsigned char)(31) - metric;

      /* Add branch metrics to path metrics */
      m0 = vec_adds(vp->old_metrics->v[i], metric);
      m3 = vec_adds(vp->old_metrics->v[8 + i], metric);
      m1 = vec_adds(vp->old_metrics->v[8 + i], m_metric);
      m2 = vec_adds(vp->old_metrics->v[i], m_metric);

      /* Compare and select first set */
      decision0 = vec_cmpgt(m0, m1);
      decision1 = vec_cmpgt(m2, m3);
      survivor0 = vec_min(m0, m1);
      survivor1 = vec_min(m2, m3);

      /* Interleave and store decisions and survivors */
      d->v[2 * i] = vec_mergeh(decision0, decision1);
      d->v[2 * i + 1] = vec_mergel(decision0, decision1);
      vp->new_metrics->v[2 * i] = vec_mergeh(survivor0, survivor1);
      vp->new_metrics->v[2 * i + 1] = vec_mergel(survivor0, survivor1);
    }
    d++;
    /* renormalize if necessary */
    if (vp->new_metrics->c[0] >= 50) {
      int i;
      vector unsigned char scale0, scale1;

      /* Find smallest metric and splat */
      scale0 = vp->new_metrics->v[0];
      scale1 = vp->new_metrics->v[1];
      for (i = 2; i < 16; i += 2) {
        scale0 = vec_min(scale0, vp->new_metrics->v[i]);
        scale1 = vec_min(scale1, vp->new_metrics->v[i + 1]);
      }
      scale0 = vec_min(scale0, scale1);
      scale0 = vec_min(scale0, vec_sld(scale0, scale0, 8));
      scale0 = vec_min(scale0, vec_sld(scale0, scale0, 4));
      scale0 = vec_min(scale0, vec_sld(scale0, scale0, 2));
      scale0 = vec_min(scale0, vec_sld(scale0, scale0, 1));

      /* Now subtract from all metrics */
      for (i = 0; i < 16; i++) {
        vp->new_metrics->v[i] = vec_subs(vp->new_metrics->v[i], scale0);
      }
    }
    /* 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;
}