1 /* K=7 r=1/2 Viterbi decoder for SSE
2 * Feb 2004, Phil Karn, KA9Q
3 */
4 #include <stdio.h>
5 #include <stdlib.h>
6 #include <memory.h>
7 #include <xmmintrin.h>
8 #include "fec.h"
9
10 typedef union { unsigned char c[64]; } metric_t;
11 typedef union { unsigned long w[2]; unsigned char c[8]; __m64 v[1];} decision_t;
12 union branchtab27 { unsigned char c[32]; __m64 v[4];} Branchtab27_sse[2];
13 static int Init = 0;
14
15 /* State info for instance of Viterbi decoder
16 * Don't change this without also changing references in ssebfly27.s!
17 */
18 struct v27 {
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 */
create_viterbi27_sse(int len)27 void *create_viterbi27_sse(int len){
28 struct v27 *vp;
29
30 if(!Init){
31 int polys[2] = { V27POLYA, V27POLYB };
32
33 set_viterbi27_polynomial_sse(polys);
34 }
35 if((vp = malloc(sizeof(struct v27))) == NULL)
36 return NULL;
37 if((vp->decisions = malloc((len+6)*sizeof(decision_t))) == NULL){
38 free(vp);
39 return NULL;
40 }
41 init_viterbi27(vp,0);
42 return vp;
43 }
44
set_viterbi27_polynomial_sse(int polys[2])45 void set_viterbi27_polynomial_sse(int polys[2]){
46 int state;
47
48 for(state=0;state < 32;state++){
49 Branchtab27_sse[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
50 Branchtab27_sse[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
51 }
52 Init++;
53 }
54
55 /* Initialize Viterbi decoder for start of new frame */
init_viterbi27_sse(void * p,int starting_state)56 int init_viterbi27_sse(void *p,int starting_state){
57 struct v27 *vp = p;
58 int i;
59
60 if(p == NULL)
61 return -1;
62 for(i=0;i<64;i++)
63 vp->metrics1.c[i] = 63;
64
65 vp->old_metrics = &vp->metrics1;
66 vp->new_metrics = &vp->metrics2;
67 vp->dp = vp->decisions;
68 vp->old_metrics->c[starting_state & 63] = 0; /* Bias known start state */
69 return 0;
70 }
71
72 /* Viterbi chainback */
chainback_viterbi27_sse(void * p,unsigned char * data,unsigned int nbits,unsigned int endstate)73 int chainback_viterbi27_sse(
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 v27 *vp = p;
79 decision_t *d;
80
81 if(p == NULL)
82 return -1;
83
84 d = vp->decisions;
85 /* Make room beyond the end of the encoder register so we can
86 * accumulate a full byte of decoded data
87 */
88 endstate %= 64;
89 endstate <<= 2;
90
91 /* The store into data[] only needs to be done every 8 bits.
92 * But this avoids a conditional branch, and the writes will
93 * combine in the cache anyway
94 */
95 d += 6; /* Look past tail */
96 while(nbits-- != 0){
97 int k;
98
99 k = (d[nbits].c[(endstate>>2)/8] >> ((endstate>>2)%8)) & 1;
100 data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
101 }
102 return 0;
103 }
104
105 /* Delete instance of a Viterbi decoder */
delete_viterbi27_sse(void * p)106 void delete_viterbi27_sse(void *p){
107 struct v27 *vp = p;
108
109 if(vp != NULL){
110 free(vp->decisions);
111 free(vp);
112 }
113 }
114