1/* K=15 r=1/6 Viterbi decoder in portable C
2 * Copyright Mar 2004, Phil Karn, KA9Q
3 * May be used under the terms of the GNU Lesser General Public License (LGPL)
4 */
5#include <stdio.h>
6#include <stdlib.h>
7#include <memory.h>
8#include <limits.h>
9#include "fec.h"
10
11typedef union { unsigned long w[512]; unsigned char c[2048];} decision_t;
12typedef union { unsigned long w[16384]; } metric_t;
13
14static union branchtab615 { unsigned long w[8192]; } Branchtab615[6] __attribute__ ((aligned(16)));
15static int Init = 0;
16
17/* State info for instance of Viterbi decoder */
18struct v615 {
19  metric_t metrics1; /* path metric buffer 1 */
20  metric_t metrics2; /* path metric buffer 2 */
21  decision_t *dp;          /* Pointer to current decision */
22  metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */
23  decision_t *decisions;   /* Beginning of decisions for block */
24};
25
26/* Create a new instance of a Viterbi decoder */
27void *create_viterbi615_port(int len){
28  struct v615 *vp;
29
30  if(!Init){
31    int polys[6] = { V615POLYA,V615POLYB,V615POLYC,V615POLYD,V615POLYE,V615POLYF };
32    set_viterbi615_polynomial_port(polys);
33  }
34  if((vp = (struct v615 *)malloc(sizeof(struct v615))) == NULL)
35    return NULL;
36  if((vp->decisions = malloc((len+14)*sizeof(decision_t))) == NULL){
37    free(vp);
38    return NULL;
39  }
40  init_viterbi615(vp,0);
41  return vp;
42}
43
44void set_viterbi615_polynomial_port(int polys[6]){
45  int state;
46  int i;
47
48  for(state=0;state < 8192;state++){
49    for(i=0;i<6;i++)
50      Branchtab615[i].w[state] = (polys[i] < 0) ^ parity((2*state) & abs(polys[i])) ? 255 : 0;
51  }
52  Init++;
53}
54
55/* Initialize Viterbi decoder for start of new frame */
56int init_viterbi615_port(void *p,int starting_state){
57  struct v615 *vp = p;
58  int i;
59
60  if(p == NULL)
61    return -1;
62  for(i=0;i<16384;i++)
63    vp->metrics1.w[i] = 1000;
64
65  vp->old_metrics = &vp->metrics1;
66  vp->new_metrics = &vp->metrics2;
67  vp->dp = vp->decisions;
68  vp->old_metrics->w[starting_state & 16383] = 0; /* Bias known start state */
69  return 0;
70}
71
72/* Viterbi chainback */
73int chainback_viterbi615_port(
74      void *p,
75      unsigned char *data, /* Decoded output data */
76      unsigned int nbits, /* Number of data bits */
77      unsigned int endstate){ /* Terminal encoder state */
78  struct v615 *vp = p;
79  decision_t *d;
80
81  if(p == NULL)
82    return -1;
83  d = (decision_t *)vp->decisions;
84  endstate %= 16384;
85
86  /* The store into data[] only needs to be done every 8 bits.
87   * But this avoids a conditional branch, and the writes will
88   * combine in the cache anyway
89   */
90  d += 14; /* Look past tail */
91  while(nbits-- != 0){
92    int k;
93
94    k = (d[nbits].c[endstate/8] >> (endstate%8)) & 1;
95    endstate = (k << 13) | (endstate >> 1);
96    data[nbits>>3] = endstate >> 6;
97  }
98  return 0;
99}
100
101/* Delete instance of a Viterbi decoder */
102void delete_viterbi615_port(void *p){
103  struct v615 *vp = p;
104
105  if(vp != NULL){
106    free(vp->decisions);
107    free(vp);
108  }
109}
110
111/* C-language butterfly */
112#define BFLY(i) {\
113unsigned long metric,m0,m1,m2,m3,decision0,decision1;\
114    metric = ((Branchtab615[0].w[i] ^ syms[0]) + (Branchtab615[1].w[i] ^ syms[1])\
115	      +(Branchtab615[2].w[i] ^ syms[2]) + (Branchtab615[3].w[i] ^ syms[3])\
116	      +(Branchtab615[4].w[i] ^ syms[4]) + (Branchtab615[5].w[i] ^ syms[5]));\
117    m0 = vp->old_metrics->w[i] + metric;\
118    m1 = vp->old_metrics->w[i+8192] + (1530 - metric);\
119    m2 = vp->old_metrics->w[i] + (1530-metric);\
120    m3 = vp->old_metrics->w[i+8192] + metric;\
121    decision0 = (signed long)(m0-m1) >= 0;\
122    decision1 = (signed long)(m2-m3) >= 0;\
123    vp->new_metrics->w[2*i] = decision0 ? m1 : m0;\
124    vp->new_metrics->w[2*i+1] = decision1 ? m3 : m2;\
125    d->c[i/4] |= ((decision0|(decision1<<1)) << ((2*i)&7));\
126}
127/* Update decoder with a block of demodulated symbols
128 * Note that nbits is the number of decoded data bits, not the number
129 * of symbols!
130 */
131
132int update_viterbi615_blk_port(void *p,unsigned char *syms,int nbits){
133  struct v615 *vp = p;
134  void *tmp;
135  decision_t *d;
136  int i;
137
138  if(p == NULL)
139    return -1;
140  d = (decision_t *)vp->dp;
141  while(nbits--){
142    memset(d,0,sizeof(decision_t));
143    for(i=0;i<8192;i++)
144      BFLY(i);
145
146    syms += 6;
147    d++;
148    /* Swap pointers to old and new metrics */
149    tmp = vp->old_metrics;
150    vp->old_metrics = vp->new_metrics;
151    vp->new_metrics = tmp;
152  }
153  vp->dp = d;
154  return 0;
155}
156
157