Extract fec-3.0.1

1 files changed, 257 insertions, 0 deletions

diff --git a/viterbi615_av.c b/viterbi615_av.c
new file mode 100644
index 0000000..4a6ce9c
--- /dev/null
+++ b/viterbi615_av.c
@@ -0,0 +1,257 @@
+/* K=15 r=1/6 Viterbi decoder for PowerPC G4/G5 Altivec vector instructions
+ * 8-bit offset-binary soft decision samples
+ * 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 char c[128][16]; vector unsigned char v[128]; } decision_t;
+typedef union { unsigned short s[16384]; vector unsigned short v[2048]; } metric_t;
+
+static union branchtab615 { unsigned short s[8192]; vector unsigned short v[1024];} Branchtab615[6];
+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 */
+  void *dp;          /* Pointer to current decision */
+  metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */
+  void *decisions;   /* Beginning of decisions for block */
+};
+
+/* Initialize Viterbi decoder for start of new frame */
+int init_viterbi615_av(void *p,int starting_state){
+  struct v615 *vp = p;
+  int i;
+
+  if(p == NULL)
+    return -1;
+
+  for(i=0;i<2048;i++)
+    vp->metrics1.v[i] = (vector unsigned short)(5000);
+
+  vp->old_metrics = &vp->metrics1;
+  vp->new_metrics = &vp->metrics2;
+  vp->dp = vp->decisions;
+  vp->old_metrics->s[starting_state & 16383] = 0; /* Bias known start state */
+  return 0;
+}
+
+/* Create a new instance of a Viterbi decoder */
+void *create_viterbi615_av(int len){
+  struct v615 *vp;
+
+  if(!Init){
+    int polys[6] = { V615POLYA,V615POLYB,V615POLYC,V615POLYD,V615POLYE,V615POLYF };
+    set_viterbi615_polynomial_av(polys);
+  }
+  vp = (struct v615 *)malloc(sizeof(struct v615));
+  vp->decisions = malloc(sizeof(decision_t)*(len+14));
+  init_viterbi615_av(vp,0);
+  return vp;
+}
+
+void set_viterbi615_polynomial_av(int polys[6]){
+  int state;
+  int i;
+
+  for(state=0;state < 8192;state++){
+    for(i=0;i<6;i++)
+      Branchtab615[i].s[state] = (polys[i] < 0) ^ parity((2*state) & abs(polys[i])) ? 255 : 0;
+  }
+  Init++;
+}
+
+
+/* Viterbi chainback */
+int chainback_viterbi615_av(
+      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 = (decision_t *)vp->decisions;
+  int path_metric;
+
+  endstate %= 16384;
+
+  path_metric = vp->old_metrics->s[endstate];
+
+  /* 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 >> 7][endstate & 15] & (0x80 >> ((endstate>>4)&7)) ) ? 1 : 0;
+    endstate = (k << 13) | (endstate >> 1);
+    data[nbits>>3] = endstate >> 6;
+  }
+  return path_metric;
+}
+
+/* Delete instance of a Viterbi decoder */
+void delete_viterbi615_av(void *p){
+  struct v615 *vp = p;
+
+  if(vp != NULL){
+    free(vp->decisions);
+    free(vp);
+  }
+}
+
+int update_viterbi615_blk_av(void *p,unsigned char *syms,int nbits){
+  struct v615 *vp = p;
+  decision_t *d = (decision_t *)vp->dp;
+  int path_metric = 0;
+  vector unsigned char decisions = (vector unsigned char)(0);
+
+  while(nbits--){
+    vector unsigned short symv,sym0v,sym1v,sym2v,sym3v,sym4v,sym5v;
+    vector unsigned char s;
+    void *tmp;
+    int i;
+    
+    /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */
+    s = (vector unsigned char)vec_perm(vec_ld(0,syms),vec_ld(5,syms),vec_lvsl(0,syms));
+
+    symv = (vector unsigned short)vec_mergeh((vector unsigned char)(0),s);    /* Unsigned byte->word unpack */ 
+    sym0v = vec_splat(symv,0);
+    sym1v = vec_splat(symv,1);
+    sym2v = vec_splat(symv,2);
+    sym3v = vec_splat(symv,3);
+    sym4v = vec_splat(symv,4);
+    sym5v = vec_splat(symv,5);
+    syms += 6;
+    
+    for(i=0;i<1024;i++){
+      vector bool short decision0,decision1;
+      vector unsigned short metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
+
+      /* Form branch metrics
+       * Because Branchtab takes on values 0 and 255, and the values of sym?v are offset binary in the range 0-255,
+       * the XOR operations constitute conditional negation.
+       * metric and m_metric (-metric) are in the range 0-1530
+       */
+      m0 = vec_add(vec_xor(Branchtab615[0].v[i],sym0v),vec_xor(Branchtab615[1].v[i],sym1v));
+      m1 = vec_add(vec_xor(Branchtab615[2].v[i],sym2v),vec_xor(Branchtab615[3].v[i],sym3v));
+      m2 = vec_add(vec_xor(Branchtab615[4].v[i],sym4v),vec_xor(Branchtab615[5].v[i],sym5v));
+      metric = vec_add(m0,m1);
+      metric = vec_add(metric,m2);
+      m_metric = vec_sub((vector unsigned short)(1530),metric);
+    
+      /* Add branch metrics to path metrics */
+      m0 = vec_adds(vp->old_metrics->v[i],metric);
+      m3 = vec_adds(vp->old_metrics->v[1024+i],metric);
+      m1 = vec_adds(vp->old_metrics->v[1024+i],m_metric);
+      m2 = vec_adds(vp->old_metrics->v[i],m_metric);
+    
+      /* Compare and select */
+      decision0 = vec_cmpgt(m0,m1);
+      decision1 = vec_cmpgt(m2,m3);
+      survivor0 = vec_min(m0,m1);
+      survivor1 = vec_min(m2,m3);
+    
+      /* Store decisions and survivors.
+       * To save space without SSE2's handy PMOVMSKB instruction, we pack and store them in
+       * a funny interleaved fashion that we undo in the chainback function.
+       */
+      decisions = vec_add(decisions,decisions); /* Shift each byte 1 bit to the left */
+
+      /* Booleans are either 0xff or 0x00. Subtracting 0x00 leaves the lsb zero; subtracting
+       * 0xff is equivalent to adding 1, which sets the lsb.
+       */
+      decisions = vec_sub(decisions,(vector unsigned char)vec_pack(vec_mergeh(decision0,decision1),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);
+
+      if((i % 8) == 7){
+	/* We've accumulated a total of 128 decisions, stash and start again */
+	d->v[i>>3] = decisions; /* No need to clear, the new bits will replace the old */
+      }
+    }
+#if 0
+    /* Experimentally determine metric spread
+     * The results are fixed for a given code and input symbol size
+     */
+    {
+      int i;
+      vector unsigned short min_metric;
+      vector unsigned short max_metric;
+      union { vector unsigned short v; unsigned short s[8];} t;
+      int minimum,maximum;
+      static int max_spread = 0;
+
+      min_metric = max_metric = vp->new_metrics->v[0];
+      for(i=1;i<2048;i++){
+	min_metric = vec_min(min_metric,vp->new_metrics->v[i]);
+	max_metric = vec_max(max_metric,vp->new_metrics->v[i]);
+      }
+      min_metric = vec_min(min_metric,vec_sld(min_metric,min_metric,8));
+      max_metric = vec_max(max_metric,vec_sld(max_metric,max_metric,8));
+      min_metric = vec_min(min_metric,vec_sld(min_metric,min_metric,4));
+      max_metric = vec_max(max_metric,vec_sld(max_metric,max_metric,4));
+      min_metric = vec_min(min_metric,vec_sld(min_metric,min_metric,2));
+      max_metric = vec_max(max_metric,vec_sld(max_metric,max_metric,2));
+
+      t.v = min_metric;
+      minimum = t.s[0];
+      t.v = max_metric;
+      maximum = t.s[0];
+      if(maximum-minimum > max_spread){
+	max_spread = maximum-minimum;
+	printf("metric spread = %d\n",max_spread);
+      }
+    }
+#endif
+
+    /* Renormalize if necessary. This deserves some explanation.
+
+     * The maximum possible spread, found by experiment, for 4-bit symbols is 405; for 8 bit symbols, it's 12750.
+     * So by looking at one arbitrary metric we can tell if any of them have possibly saturated.
+     * However, this is very conservative. Large spreads occur only at very high Eb/No, where
+     * saturating a bad path metric doesn't do much to increase its chances of being erroneously chosen as a survivor.
+
+     * At more interesting (low) Eb/No ratios, the spreads are much smaller so our chances of saturating a metric
+     * by not not normalizing when we should are extremely low. So either way, the risk to performance is small.
+
+     * All this is borne out by experiment.
+     */
+    if(vp->new_metrics->s[0] >= USHRT_MAX-12750){
+      vector unsigned short scale;
+      union { vector unsigned short v; unsigned short s[8];} t;
+      
+      /* Find smallest metric and splat */
+      scale = vp->new_metrics->v[0];
+      for(i=1;i<2048;i++)
+	scale = vec_min(scale,vp->new_metrics->v[i]);
+
+      scale = vec_min(scale,vec_sld(scale,scale,8));
+      scale = vec_min(scale,vec_sld(scale,scale,4));
+      scale = vec_min(scale,vec_sld(scale,scale,2));
+
+      /* Subtract it from all metrics
+       * Work backwards to try to improve the cache hit ratio, assuming LRU
+       */
+      for(i=2047;i>=0;i--)
+	vp->new_metrics->v[i] = vec_subs(vp->new_metrics->v[i],scale);
+      t.v = scale;
+      path_metric += t.s[0];
+    }
+    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 path_metric;
+}