Extract fec-3.0.1

1 files changed, 168 insertions, 0 deletions

diff --git a/viterbi39_port.c b/viterbi39_port.c
new file mode 100644
index 0000000..5685c90
--- /dev/null
+++ b/viterbi39_port.c
@@ -0,0 +1,168 @@
+/* K=9 r=1/3 Viterbi decoder in portable C
+ * Copyright Aug 2006, 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 "fec.h"
+
+typedef union { unsigned int w[256]; } metric_t;
+typedef union { unsigned long w[8];} decision_t;
+
+static union { unsigned char c[128]; } 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 */
+  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_viterbi39_port(void *p,int starting_state){
+  struct v39 *vp = p;
+  int i;
+
+  if(p == NULL)
+    return -1;
+  for(i=0;i<256;i++)
+    vp->metrics1.w[i] = 63;
+
+  vp->old_metrics = &vp->metrics1;
+  vp->new_metrics = &vp->metrics2;
+  vp->dp = vp->decisions;
+  vp->old_metrics->w[starting_state & 255] = 0; /* Bias known start state */
+  return 0;
+}
+
+void set_viterbi39_polynomial_port(int polys[3]){
+  int state;
+
+  for(state=0;state < 128;state++){
+    Branchtab39[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
+    Branchtab39[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
+    Branchtab39[2].c[state] = (polys[2] < 0) ^ parity((2*state) & abs(polys[2])) ? 255 : 0;
+  }
+  Init++;
+}
+
+/* Create a new instance of a Viterbi decoder */
+void *create_viterbi39_port(int len){
+  struct v39 *vp;
+
+  if(!Init){
+    int polys[3] = {V39POLYA,V39POLYB,V39POLYC};
+    set_viterbi39_polynomial_port(polys);
+  }
+  if((vp = (struct v39 *)malloc(sizeof(struct v39))) == NULL)
+    return NULL;
+
+  if((vp->decisions = (decision_t *)malloc((len+8)*sizeof(decision_t))) == NULL){
+    free(vp);
+    return NULL;
+  }
+  init_viterbi39_port(vp,0);
+
+  return vp;
+}
+
+
+/* Viterbi chainback */
+int chainback_viterbi39_port(
+      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;
+
+  if(p == NULL)
+    return -1;
+
+  d = 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].w[(endstate)/32] >> (endstate%32)) & 1;
+    data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
+  }
+  return 0;
+}
+
+
+/* Delete instance of a Viterbi decoder */
+void delete_viterbi39_port(void *p){
+  struct v39 *vp = p;
+
+  if(vp != NULL){
+    free(vp->decisions);
+    free(vp);
+  }
+}
+
+/* C-language butterfly */
+#define BFLY(i) {\
+unsigned int metric,m0,m1,decision;\
+    metric = (Branchtab39[0].c[i] ^ sym0) + (Branchtab39[1].c[i] ^ sym1) + \
+     (Branchtab39[2].c[i] ^ sym2);\
+    m0 = vp->old_metrics->w[i] + metric;\
+    m1 = vp->old_metrics->w[i+128] + (765 - metric);\
+    decision = (signed int)(m0-m1) > 0;\
+    vp->new_metrics->w[2*i] = decision ? m1 : m0;\
+    d->w[i/16] |= decision << ((2*i)&31);\
+    m0 -= (metric+metric-765);\
+    m1 += (metric+metric-765);\
+    decision = (signed int)(m0-m1) > 0;\
+    vp->new_metrics->w[2*i+1] = decision ? m1 : m0;\
+    d->w[i/16] |= decision << ((2*i+1)&31);\
+}
+
+/* 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_viterbi39_blk_port(void *p,unsigned char *syms,int nbits){
+  struct v39 *vp = p;
+  decision_t *d;
+
+  if(p == NULL)
+    return -1;
+  
+  d = (decision_t *)vp->dp;
+  while(nbits--){
+    void *tmp;
+    unsigned char sym0,sym1,sym2;
+    int i;
+
+    for(i=0;i<8;i++)
+      d->w[i] = 0;
+    sym0 = *syms++;
+    sym1 = *syms++;
+    sym2 = *syms++;
+
+    for(i=0;i<128;i++)
+      BFLY(i);
+
+    d++;
+    tmp = vp->old_metrics;
+    vp->old_metrics = vp->new_metrics;
+    vp->new_metrics = tmp;
+  }  
+  vp->dp = d;
+  return 0;
+}