Extract fec-3.0.1

1 files changed, 185 insertions, 0 deletions

diff --git a/viterbi39_mmx.c b/viterbi39_mmx.c
new file mode 100644
index 0000000..875391a
--- /dev/null
+++ b/viterbi39_mmx.c
@@ -0,0 +1,185 @@
+/* K=9 r=1/3 Viterbi decoder for x86 MMX
+ * Aug 2006, Phil Karn, KA9Q
+ * May be used under the terms of the GNU Lesser General Public License (LGPL)
+ */
+#include <mmintrin.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <memory.h>
+#include "fec.h"
+
+typedef union { unsigned char c[256]; __m64 v[32];} decision_t;
+typedef union { unsigned short s[256]; __m64 v[64];} metric_t;
+
+static union branchtab39 { unsigned short s[128]; __m64 v[32];} Branchtab39[3];
+static int Init = 0;
+
+/* State info for instance of Viterbi decoder */
+struct v39 {
+  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_viterbi39_mmx(void *p,int starting_state){
+  struct v39 *vp = p;
+  int i;
+
+  if(p == NULL)
+    return -1;
+  for(i=0;i<256;i++)
+    vp->metrics1.s[i] = 1000;
+
+  vp->old_metrics = &vp->metrics1;
+  vp->new_metrics = &vp->metrics2;
+  vp->dp = vp->decisions;
+  vp->old_metrics->s[starting_state & 255] = 0; /* Bias known start state */
+  return 0;
+}
+
+void set_viterbi39_polynomial_mmx(int polys[3]){
+  int state;
+
+  for(state=0;state < 128;state++){
+    Branchtab39[0].s[state] = (polys[0] < 0) ^ parity((2*state) & polys[0]) ? 255:0;
+    Branchtab39[1].s[state] = (polys[1] < 0) ^ parity((2*state) & polys[1]) ? 255:0;
+    Branchtab39[2].s[state] = (polys[2] < 0) ^ parity((2*state) & polys[2]) ? 255:0;
+  }
+  Init++;
+}
+
+/* Create a new instance of a Viterbi decoder */
+void *create_viterbi39_mmx(int len){
+  struct v39 *vp;
+
+  if(!Init){
+    int polys[3] = { V39POLYA,V39POLYB,V39POLYC };
+    set_viterbi39_polynomial_mmx(polys);
+  }
+  if((vp = (struct v39 *)malloc(sizeof(struct v39))) == NULL)
+    return NULL;
+  if((vp->decisions = malloc((len+8)*sizeof(decision_t))) == NULL){
+    free(vp);
+    return NULL;
+  }
+  init_viterbi39_mmx(vp,0);
+  return vp;
+}
+
+
+
+/* Viterbi chainback */
+int chainback_viterbi39_mmx(
+      void *p,
+      unsigned char *data, /* Decoded output data */
+      unsigned int nbits, /* Number of data bits */
+      unsigned int endstate){ /* Terminal encoder state */
+  struct v39 *vp = p;
+  decision_t *d;
+  int path_metric;
+
+  if(p == NULL)
+    return -1;
+
+  d = (decision_t *)vp->decisions;
+  
+  endstate %= 256;
+
+  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 += 8; /* Look past tail */
+  while(nbits-- != 0){
+    int k;
+
+    k = d[nbits].c[endstate] & 1;
+    endstate = (k << 7) | (endstate >> 1);
+    data[nbits>>3] = endstate;
+  }
+  return path_metric;
+}
+
+/* Delete instance of a Viterbi decoder */
+void delete_viterbi39_mmx(void *p){
+  struct v39 *vp = p;
+
+  if(vp != NULL){
+    free(vp->decisions);
+    free(vp);
+  }
+}
+
+
+int update_viterbi39_blk_mmx(void *p,unsigned char *syms,int nbits){
+  struct v39 *vp = p;
+  decision_t *d;
+  int path_metric = 0;
+
+  if(p == NULL)
+    return -1;
+
+  d = (decision_t *)vp->dp;
+  
+  while(nbits--){
+    __m64 sym0v,sym1v,sym2v;
+    void *tmp;
+    int i;
+    
+    /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */
+    sym0v = _mm_set1_pi16(syms[0]);
+    sym1v = _mm_set1_pi16(syms[1]);
+    sym2v = _mm_set1_pi16(syms[2]);
+    syms += 3;
+
+    for(i=0;i<32;i++){
+      __m64 decision0,decision1,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 = _mm_add_pi16(_mm_xor_si64(Branchtab39[0].v[i],sym0v),_mm_xor_si64(Branchtab39[1].v[i],sym1v));
+      metric = _mm_add_pi16(_mm_xor_si64(Branchtab39[2].v[i],sym2v),m0);
+      m_metric = _mm_sub_pi16(_mm_set1_pi16(765),metric);
+    
+      /* Add branch metrics to path metrics */
+      m0 = _mm_add_pi16(vp->old_metrics->v[i],metric);
+      m3 = _mm_add_pi16(vp->old_metrics->v[32+i],metric);
+      m1 = _mm_add_pi16(vp->old_metrics->v[32+i],m_metric);
+      m2 = _mm_add_pi16(vp->old_metrics->v[i],m_metric);
+    
+      /* Compare and select
+       * There's no packed min instruction in MMX, so we use modulo arithmetic
+       * to form the decisions and then do the select the hard way
+       */
+      decision0 = _mm_cmpgt_pi16(_mm_sub_pi16(m0,m1),_mm_setzero_si64());
+      decision1 = _mm_cmpgt_pi16(_mm_sub_pi16(m2,m3),_mm_setzero_si64());
+      survivor0 = _mm_or_si64(_mm_and_si64(decision0,m1),_mm_andnot_si64(decision0,m0));
+      survivor1 = _mm_or_si64(_mm_and_si64(decision1,m3),_mm_andnot_si64(decision1,m2));
+ 
+      /* Merge decisions and store as bytes */
+      d->v[i] = _mm_unpacklo_pi8(_mm_packs_pi16(decision0,_mm_setzero_si64()),_mm_packs_pi16(decision1,_mm_setzero_si64()));
+
+      /* Store surviving metrics */
+      vp->new_metrics->v[2*i] = _mm_unpacklo_pi16(survivor0,survivor1);
+      vp->new_metrics->v[2*i+1] = _mm_unpackhi_pi16(survivor0,survivor1);
+    }
+    if(vp->new_metrics->s[0] < vp->old_metrics->s[0])
+      path_metric += 65536; /* Hack: wraparound probably occured */
+    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;
+  _mm_empty();
+  return path_metric;
+}