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
12 typedef union { unsigned int w[64]; } metric_t;
13 typedef union { unsigned long w[2];} decision_t;
14 static union branchtab27 { unsigned char c[32]; } Branchtab27[2] __attribute__ ((aligned(16)));
15 static 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 */
20 struct 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 */
init_viterbi27_port(void * p,int starting_state)29 int 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
set_viterbi27_polynomial_port(int polys[2])45 void 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 */
create_viterbi27_port(int len)56 void *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 */
chainback_viterbi27_port(void * p,unsigned char * data,unsigned int nbits,unsigned int endstate)75 int 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 */
delete_viterbi27_port(void * p)107 void 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) {\
118 unsigned 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 */
update_viterbi27_blk_port(void * p,unsigned char * syms,int nbits)136 int 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