1 /* K=9 r=1/2 Viterbi decoder for SSE2
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 <emmintrin.h>
9 #include "fec.h"
10
11 typedef union { unsigned char c[256]; __m128i v[16];} metric_t;
12 typedef union { unsigned long w[8]; unsigned char c[32];} decision_t;
13
14 union branchtab29 { unsigned char c[128]; } Branchtab29_sse2[2];
15 static int Init = 0;
16
17 /* State info for instance of Viterbi decoder
18 * Don't change this without also changing references in sse2bfly29.s!
19 */
20 struct v29 {
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_viterbi29_sse2(void * p,int starting_state)29 int init_viterbi29_sse2(void *p,int starting_state){
30 struct v29 *vp = p;
31 int i;
32
33 for(i=0;i<256;i++)
34 vp->metrics1.c[i] = 63;
35
36 vp->old_metrics = &vp->metrics1;
37 vp->new_metrics = &vp->metrics2;
38 vp->dp = vp->decisions;
39 vp->old_metrics->c[starting_state & 255] = 0; /* Bias known start state */
40 return 0;
41 }
42
set_viterbi29_polynomial_sse2(int polys[2])43 void set_viterbi29_polynomial_sse2(int polys[2]){
44 int state;
45
46 for(state=0;state < 128;state++){
47 Branchtab29_sse2[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
48 Branchtab29_sse2[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
49 }
50 Init++;
51 }
52
53
54 /* Create a new instance of a Viterbi decoder */
create_viterbi29_sse2(int len)55 void *create_viterbi29_sse2(int len){
56 void *p;
57 struct v29 *vp;
58
59 if(!Init){
60 int polys[2] = {V29POLYA,V29POLYB};
61
62 set_viterbi29_polynomial(polys);
63 }
64 /* Ordinary malloc() only returns 8-byte alignment, we need 16 */
65 if(posix_memalign(&p, sizeof(__m128i),sizeof(struct v29)))
66 return NULL;
67 vp = (struct v29 *)p;
68 if((p = malloc((len+8)*sizeof(decision_t))) == NULL){
69 free(vp);
70 return NULL;
71 }
72 vp->decisions = (decision_t *)p;
73 init_viterbi29_sse2(vp,0);
74 return vp;
75 }
76
77
78 /* Viterbi chainback */
chainback_viterbi29_sse2(void * p,unsigned char * data,unsigned int nbits,unsigned int endstate)79 int chainback_viterbi29_sse2(
80 void *p,
81 unsigned char *data, /* Decoded output data */
82 unsigned int nbits, /* Number of data bits */
83 unsigned int endstate){ /* Terminal encoder state */
84 struct v29 *vp = p;
85 decision_t *d;
86
87 if(p == NULL)
88 return -1;
89 d = vp->decisions;
90
91 /* Make room beyond the end of the encoder register so we can
92 * accumulate a full byte of decoded data
93 */
94 endstate %= 256;
95
96 /* The store into data[] only needs to be done every 8 bits.
97 * But this avoids a conditional branch, and the writes will
98 * combine in the cache anyway
99 */
100 d += 8; /* Look past tail */
101 while(nbits-- != 0){
102 int k;
103
104 k = (d[nbits].c[endstate/8] >> (endstate%8)) & 1;
105 data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
106 }
107 return 0;
108 }
109
110
111 /* Delete instance of a Viterbi decoder */
delete_viterbi29_sse2(void * p)112 void delete_viterbi29_sse2(void *p){
113 struct v29 *vp = p;
114
115 if(vp != NULL){
116 free(vp->decisions);
117 free(vp);
118 }
119 }
120