1 /* K=7 r=1/2 Viterbi decoder for MMX
2 * Copyright Feb 2004, Phil Karn, KA9Q
3 */
4 #include <stdio.h>
5 #include <stdlib.h>
6 #include <memory.h>
7 #include <mmintrin.h>
8 #include "fec.h"
9
10 typedef union { char c[64]; __m64 v[8];} decision_t;
11 typedef union { unsigned char c[64]; __m64 v[8];} metric_t;
12
13 unsigned char Mettab27_1[256][32] __attribute__ ((aligned(16)));
14 unsigned char Mettab27_2[256][32] __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 mmxbfly27.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_mmx(void * p,int starting_state)29 int init_viterbi27_mmx(void *p,int starting_state){
30 struct v27 *vp = (struct v27 *)p;
31 int i;
32
33 if(p == NULL)
34 return -1;
35 for(i=0;i<64;i++)
36 vp->metrics1.c[i] = 63;
37
38 vp->old_metrics = &vp->metrics1;
39 vp->new_metrics = &vp->metrics2;
40 vp->dp = vp->decisions;
41 vp->old_metrics->c[starting_state & 63] = 0; /* Bias known start state */
42 return 0;
43 }
44
set_viterbi27_polynomial_mmx(int polys[2])45 void set_viterbi27_polynomial_mmx(int polys[2]){
46 int state;
47
48 for(state=0;state < 32;state++){
49 int symbol;
50 for(symbol = 0;symbol < 256;symbol++){
51 int sym;
52
53 sym = parity((2*state) & abs(polys[0])) ^ (polys[0] < 0);
54 Mettab27_1[symbol][state] = (sym ? (255-symbol):symbol) / 16;
55
56 sym = parity((2*state) & abs(polys[1])) ^ (polys[1] < 0);
57 Mettab27_2[symbol][state] = (sym ? (255-symbol):symbol) / 16;
58 }
59 }
60 Init++;
61 }
62
63
64 /* Create a new instance of a Viterbi decoder */
create_viterbi27_mmx(int len)65 void *create_viterbi27_mmx(int len){
66 struct v27 *vp;
67 int polys[2] = { V27POLYA, V27POLYB };
68
69 if(Init == 0){
70 set_viterbi27_polynomial_mmx(polys);
71 }
72 if((vp = (struct v27 *)malloc(sizeof(struct v27))) == NULL)
73 return NULL;
74
75 if((vp->decisions = (decision_t *)malloc((len+6)*sizeof(decision_t))) == NULL){
76 free(vp);
77 return NULL;
78 }
79 init_viterbi27_mmx(vp,0);
80 return vp;
81 }
82
83 /* Viterbi chainback */
chainback_viterbi27_mmx(void * p,unsigned char * data,unsigned int nbits,unsigned int endstate)84 int chainback_viterbi27_mmx(
85 void *p,
86 unsigned char *data, /* Decoded output data */
87 unsigned int nbits, /* Number of data bits */
88 unsigned int endstate){ /* Terminal encoder state */
89
90 struct v27 *vp = (struct v27 *)p;
91 decision_t *d;
92
93 if(p == NULL)
94 return -1;
95 d = (decision_t *)vp->decisions;
96 endstate &= 63;
97 d += 6; /* Look past tail */
98 while(nbits-- != 0){
99 int k;
100
101 k = d[nbits].c[endstate>>2] & 1;
102 data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
103 }
104 return 0;
105 }
106
107 /* Delete instance of a Viterbi decoder */
delete_viterbi27_mmx(void * p)108 void delete_viterbi27_mmx(void *p){
109 struct v27 *vp = p;
110
111 if(vp != NULL){
112 free(vp->decisions);
113 free(vp);
114 }
115 }
116