init commit

2026-08-25 17:27:34 +00:00 · 2026-06-22 11:39:50 +03:00
commit ba6f1bde22
128 changed files with 17716 additions and 0 deletions
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+/* K=24 r=1/2 Viterbi decoder in portable C
+ * Copyright Mar 2014, 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 <stdint.h>
+#include "fec.h"
+#include "code.h"
+
+// Portable version of 32-bit parity
+static inline int parity(int x){
+  x ^= x >> 16;
+  x ^= x >> 8;
+  x ^= x >> 4;
+  x ^= x >> 2;
+  return (x ^ (x >> 1)) & 1;
+}
+
+
+
+typedef union { uint32_t w[1<<(K-6)]; uint8_t c[1<<(K-4)];} decision_t;
+typedef union { uint32_t w[1<<(K-1)]; } metric_t;
+
+static union branchtab224 { uint32_t w[1<<(K-2)]; } Branchtab224[2] __attribute__ ((aligned(16)));
+
+/* State info for instance of Viterbi decoder */
+struct v224 {
+  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_viterbi224(void *p,int starting_state){
+  struct v224 *vp = p;
+  int i;
+
+  if(p == NULL)
+    return -1;
+  for(i=0;i<(1<<(K-1));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 & ((1<<(K-1))-1)] = 0; /* Bias known start state */
+  return 0;
+}
+
+/* Create a new instance of a Viterbi decoder */
+void *create_viterbi224(int len){
+  struct v224 *vp;
+  int state;
+
+  if((vp = (struct v224 *)malloc(sizeof(struct v224))) == NULL)
+    return NULL;
+  if((vp->decisions = malloc(len*sizeof(decision_t))) == NULL){
+    free(vp);
+    return NULL;
+  }
+  for(state=0;state < (1<<(K-2));state++){
+    Branchtab224[0].w[state] = G1FLIP ^ parity((2*state) & POLY1) ? 255 : 0;
+    Branchtab224[1].w[state] = G2FLIP ^ parity((2*state) & POLY2) ? 255 : 0;
+  }
+  init_viterbi224(vp,0);
+  return vp;
+}
+
+
+/* Viterbi chainback */
+int chainback_viterbi224(
+      void *p,
+      unsigned char *data, /* Decoded output data */
+      unsigned int nbits, /* Number of data bits */
+      unsigned int endstate){ /* Terminal encoder state */
+  struct v224 *vp = p;
+  decision_t *d;
+
+  if(p == NULL)
+    return -1;
+  d = (decision_t *)vp->decisions;  
+  endstate &= (1<<(K-1))-1;
+
+  unsigned char dbyte = 0;
+  while(nbits-- != 0){
+    int bit;
+
+    // Accumulate decoded data bits as they fall off the right end of endstate
+    dbyte = ((endstate & 1) << 7) | (dbyte >> 1);
+    if((nbits & 7) == 0)
+      data[nbits>>3] = dbyte;
+
+    // Shift new bit into left end of endstate
+    bit = (d[nbits].c[endstate >> 3] >> (endstate & 7)) & 1;
+    endstate = (bit << (K-2)) | (endstate >> 1);
+  }
+  return 0;
+}
+
+/* Delete instance of a Viterbi decoder */
+void delete_viterbi224(void *p){
+  struct v224 *vp = p;
+
+  if(vp != NULL){
+    free(vp->decisions);
+    free(vp);
+  }
+}
+
+/* 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_viterbi224_blk(void *p,const unsigned char *syms,int nbits){
+  struct v224 *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<(1<<(K-2));i++){
+      unsigned long metric,m0,m1,m2,m3,decision0,decision1;
+
+      metric = ((Branchtab224[0].w[i] ^ syms[0]) + (Branchtab224[1].w[i] ^ syms[1]));
+      m0 = vp->old_metrics->w[i] + metric;
+      m1 = vp->old_metrics->w[i+(1<<(K-2))] + (510 - metric);
+      m2 = vp->old_metrics->w[i] + (510-metric);
+      m3 = vp->old_metrics->w[i+(1<<(K-2))] + 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));
+    }
+    syms += 2;
+    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;
+}
+