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1 /* K=9 r=1/2 Viterbi decoder for SSE
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 <xmmintrin.h>
9 #include "fec.h"
10 
11 typedef union { unsigned char w[256]; __m64 v[32];} metric_t;
12 typedef union { unsigned long w[8]; unsigned char c[32]; __m64 v[4];} decision_t;
13 
14 union branchtab29 { unsigned char c[128]; } Branchtab29_sse[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 [mmx|sse|sse2]bfly29.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 /* Create a new instance of a Viterbi decoder */
create_viterbi29_sse(int len)29 void *create_viterbi29_sse(int len){
30   struct v29 *vp;
31 
32   if(!Init){
33     int polys[2] = { V29POLYA,V29POLYB };
34 
35     set_viterbi29_polynomial_sse(polys);
36   }
37   if((vp = (struct v29 *)malloc(sizeof(struct v29))) == NULL)
38     return NULL;
39   if((vp->decisions = (decision_t *)malloc((len+8)*sizeof(decision_t))) == NULL){
40     free(vp);
41     return NULL;
42   }
43   init_viterbi29(vp,0);
44   return vp;
45 }
46 
set_viterbi29_polynomial_sse(int polys[2])47 void set_viterbi29_polynomial_sse(int polys[2]){
48   int state;
49 
50   for(state=0;state < 128;state++){
51     Branchtab29_sse[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
52     Branchtab29_sse[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
53   }
54   Init++;
55 }
56 
57 /* Initialize Viterbi decoder for start of new frame */
init_viterbi29_sse(void * p,int starting_state)58 int init_viterbi29_sse(void *p,int starting_state){
59   struct v29 *vp = p;
60   int i;
61 
62   if(p == NULL)
63     return -1;
64   for(i=0;i<256;i++)
65     vp->metrics1.w[i] = 200;
66 
67   vp->old_metrics = &vp->metrics1;
68   vp->new_metrics = &vp->metrics2;
69   vp->dp = vp->decisions;
70   vp->old_metrics->w[starting_state & 255] = 0; /* Bias known start state */
71   return 0;
72 }
73 
74 /* Viterbi chainback */
chainback_viterbi29_sse(void * p,unsigned char * data,unsigned int nbits,unsigned int endstate)75 int chainback_viterbi29_sse(
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 v29 *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 %= 256;
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 += 8; /* Look past tail */
96   while(nbits-- != 0){
97     int k;
98 
99     k = (d[nbits].c[endstate/8] >> (endstate%8)) & 1;
100     data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
101   }
102   return 0;
103 }
104 
105 
106 /* Delete instance of a Viterbi decoder */
delete_viterbi29_sse(void * p)107 void delete_viterbi29_sse(void *p){
108   struct v29 *vp = p;
109 
110   if(vp != NULL){
111     free(vp->decisions);
112     free(vp);
113   }
114 }
115