1/* K=7 r=1/2 Viterbi decoder in portable C
2 * Copyright Feb 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
11
12typedef union { unsigned int w[64]; } metric_t;
13typedef union { unsigned long w[2];} decision_t;
14static union branchtab27 { unsigned char c[32]; } Branchtab27[2] __attribute__ ((aligned(16)));
15static int Init = 0;
16
17/* State info for instance of Viterbi decoder
18 * Don't change this without also changing references in [mmx|sse|sse2]bfly29.s!
19 */
20struct v27 {
21  metric_t metrics1; /* path metric buffer 1 */
22  metric_t metrics2; /* path metric buffer 2 */
23  decision_t *dp;          /* Pointer to current decision */
24  metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */
25  decision_t *decisions;   /* Beginning of decisions for block */
26};
27
28/* Initialize Viterbi decoder for start of new frame */
29int init_viterbi27_port(void *p,int starting_state){
30  struct v27 *vp = p;
31  int i;
32
33  if(p == NULL)
34    return -1;
35  for(i=0;i<64;i++)
36    vp->metrics1.w[i] = 63;
37
38  vp->old_metrics = &vp->metrics1;
39  vp->new_metrics = &vp->metrics2;
40  vp->dp = vp->decisions;
41  vp->old_metrics->w[starting_state & 63] = 0; /* Bias known start state */
42  return 0;
43}
44
45void set_viterbi27_polynomial_port(int polys[2]){
46  int state;
47
48  for(state=0;state < 32;state++){
49    Branchtab27[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
50    Branchtab27[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
51  }
52  Init++;
53}
54
55/* Create a new instance of a Viterbi decoder */
56void *create_viterbi27_port(int len){
57  struct v27 *vp;
58
59  if(!Init){
60    int polys[2] = { V27POLYA, V27POLYB };
61    set_viterbi27_polynomial_port(polys);
62  }
63  if((vp = malloc(sizeof(struct v27))) == NULL)
64     return NULL;
65  if((vp->decisions = malloc((len+6)*sizeof(decision_t))) == NULL){
66    free(vp);
67    return NULL;
68  }
69  init_viterbi27_port(vp,0);
70
71  return vp;
72}
73
74/* Viterbi chainback */
75int chainback_viterbi27_port(
76      void *p,
77      unsigned char *data, /* Decoded output data */
78      unsigned int nbits, /* Number of data bits */
79      unsigned int endstate){ /* Terminal encoder state */
80  struct v27 *vp = p;
81  decision_t *d;
82
83  if(p == NULL)
84    return -1;
85  d = vp->decisions;
86  /* Make room beyond the end of the encoder register so we can
87   * accumulate a full byte of decoded data
88   */
89  endstate %= 64;
90  endstate <<= 2;
91
92  /* The store into data[] only needs to be done every 8 bits.
93   * But this avoids a conditional branch, and the writes will
94   * combine in the cache anyway
95   */
96  d += 6; /* Look past tail */
97  while(nbits-- != 0){
98    int k;
99
100    k = (d[nbits].w[(endstate>>2)/32] >> ((endstate>>2)%32)) & 1;
101    data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
102  }
103  return 0;
104}
105
106/* Delete instance of a Viterbi decoder */
107void delete_viterbi27_port(void *p){
108  struct v27 *vp = p;
109
110  if(vp != NULL){
111    free(vp->decisions);
112    free(vp);
113  }
114}
115
116/* C-language butterfly */
117#define BFLY(i) {\
118unsigned int metric,m0,m1,decision;\
119    metric = (Branchtab27[0].c[i] ^ sym0) + (Branchtab27[1].c[i] ^ sym1);\
120    m0 = vp->old_metrics->w[i] + metric;\
121    m1 = vp->old_metrics->w[i+32] + (510 - metric);\
122    decision = (signed int)(m0-m1) > 0;\
123    vp->new_metrics->w[2*i] = decision ? m1 : m0;\
124    d->w[i/16] |= decision << ((2*i)&31);\
125    m0 -= (metric+metric-510);\
126    m1 += (metric+metric-510);\
127    decision = (signed int)(m0-m1) > 0;\
128    vp->new_metrics->w[2*i+1] = decision ? m1 : m0;\
129    d->w[i/16] |= decision << ((2*i+1)&31);\
130}
131
132/* Update decoder with a block of demodulated symbols
133 * Note that nbits is the number of decoded data bits, not the number
134 * of symbols!
135 */
136int update_viterbi27_blk_port(void *p,unsigned char *syms,int nbits){
137  struct v27 *vp = p;
138  void *tmp;
139  decision_t *d;
140
141  if(p == NULL)
142    return -1;
143  d = (decision_t *)vp->dp;
144  while(nbits--){
145    unsigned char sym0,sym1;
146
147    d->w[0] = d->w[1] = 0;
148    sym0 = *syms++;
149    sym1 = *syms++;
150
151    BFLY(0);
152    BFLY(1);
153    BFLY(2);
154    BFLY(3);
155    BFLY(4);
156    BFLY(5);
157    BFLY(6);
158    BFLY(7);
159    BFLY(8);
160    BFLY(9);
161    BFLY(10);
162    BFLY(11);
163    BFLY(12);
164    BFLY(13);
165    BFLY(14);
166    BFLY(15);
167    BFLY(16);
168    BFLY(17);
169    BFLY(18);
170    BFLY(19);
171    BFLY(20);
172    BFLY(21);
173    BFLY(22);
174    BFLY(23);
175    BFLY(24);
176    BFLY(25);
177    BFLY(26);
178    BFLY(27);
179    BFLY(28);
180    BFLY(29);
181    BFLY(30);
182    BFLY(31);
183    d++;
184    /* Swap pointers to old and new metrics */
185    tmp = vp->old_metrics;
186    vp->old_metrics = vp->new_metrics;
187    vp->new_metrics = tmp;
188  }
189  vp->dp = d;
190  return 0;
191}
192