1 /* K=9 r=1/3 Viterbi decoder for x86 SSE
2 * Copyright Aug 2006, Phil Karn, KA9Q
3 * May be used under the terms of the GNU Lesser General Public License (LGPL)
4 */
5 #include <xmmintrin.h>
6 #include <stdio.h>
7 #include <stdlib.h>
8 #include <memory.h>
9 #include <limits.h>
10 #include "fec.h"
11
12 typedef union { unsigned long w[8]; unsigned char c[32];} decision_t;
13 typedef union { signed short s[256]; __m64 v[64];} metric_t;
14
15 static union branchtab39 { unsigned short s[128]; __m64 v[32];} Branchtab39[3];
16 static int Init = 0;
17
18 /* State info for instance of Viterbi decoder */
19 struct v39 {
20 metric_t metrics1; /* path metric buffer 1 */
21 metric_t metrics2; /* path metric buffer 2 */
22 void *dp; /* Pointer to current decision */
23 metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */
24 void *decisions; /* Beginning of decisions for block */
25 };
26
27 /* Initialize Viterbi decoder for start of new frame */
init_viterbi39_sse(void * p,int starting_state)28 int init_viterbi39_sse(void *p,int starting_state){
29 struct v39 *vp = p;
30 int i;
31
32 if(p == NULL)
33 return -1;
34 for(i=0;i<256;i++)
35 vp->metrics1.s[i] = (SHRT_MIN+1000);
36
37 vp->old_metrics = &vp->metrics1;
38 vp->new_metrics = &vp->metrics2;
39 vp->dp = vp->decisions;
40 vp->old_metrics->s[starting_state & 255] = SHRT_MIN; /* Bias known start state */
41 return 0;
42 }
43
44 /* Create a new instance of a Viterbi decoder */
create_viterbi39_sse(int len)45 void *create_viterbi39_sse(int len){
46 struct v39 *vp;
47
48 if(!Init){
49 int polys[3] = { V39POLYA, V39POLYB, V39POLYC };
50
51 set_viterbi39_polynomial_sse(polys);
52 }
53 if((vp = (struct v39 *)malloc(sizeof(struct v39))) == NULL){
54 return NULL;
55 }
56 if((vp->decisions = malloc((len+8)*sizeof(decision_t))) == NULL){
57 free(vp);
58 return NULL;
59 }
60 init_viterbi39_sse(vp,0);
61 return vp;
62 }
63
set_viterbi39_polynomial_sse(int polys[3])64 void set_viterbi39_polynomial_sse(int polys[3]){
65 int state;
66
67 for(state=0;state < 128;state++){
68 Branchtab39[0].s[state] = (polys[0] < 0) ^ parity((2*state) & polys[0]) ? 255:0;
69 Branchtab39[1].s[state] = (polys[1] < 0) ^ parity((2*state) & polys[1]) ? 255:0;
70 Branchtab39[2].s[state] = (polys[2] < 0) ^ parity((2*state) & polys[2]) ? 255:0;
71 }
72 Init++;
73 }
74
75 /* Viterbi chainback */
chainback_viterbi39_sse(void * p,unsigned char * data,unsigned int nbits,unsigned int endstate)76 int chainback_viterbi39_sse(
77 void *p,
78 unsigned char *data, /* Decoded output data */
79 unsigned int nbits, /* Number of data bits */
80 unsigned int endstate){ /* Terminal encoder state */
81 struct v39 *vp = p;
82 decision_t *d;
83 int path_metric;
84
85 if(p == NULL)
86 return -1;
87 d = (decision_t *)vp->decisions;
88 endstate %= 256;
89
90 path_metric = vp->old_metrics->s[endstate];
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 += 8; /* Look past tail */
97 while(nbits-- != 0){
98 int k;
99
100 /* k = (d[nbits].w[endstate/32] >> (endstate%32)) & 1;*/
101 k = (d[nbits].c[endstate/8] >> (endstate%8)) & 1;
102 endstate = (k << 7) | (endstate >> 1);
103 data[nbits>>3] = endstate;
104 }
105 return path_metric - SHRT_MIN;
106 }
107
108 /* Delete instance of a Viterbi decoder */
delete_viterbi39_sse(void * p)109 void delete_viterbi39_sse(void *p){
110 struct v39 *vp = p;
111
112 if(vp != NULL){
113 free(vp->decisions);
114 free(vp);
115 }
116 }
117
118
update_viterbi39_blk_sse(void * p,unsigned char * syms,int nbits)119 int update_viterbi39_blk_sse(void *p,unsigned char *syms,int nbits){
120 struct v39 *vp = p;
121 decision_t *d;
122 int path_metric = 0;
123
124 if(p == NULL)
125 return -1;
126 d = (decision_t *)vp->dp;
127 while(nbits--){
128 __m64 sym0v,sym1v,sym2v;
129 void *tmp;
130 int i;
131
132 /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */
133 sym0v = _mm_set1_pi16(syms[0]);
134 sym1v = _mm_set1_pi16(syms[1]);
135 sym2v = _mm_set1_pi16(syms[2]);
136 syms += 3;
137
138 for(i=0;i<32;i++){
139 __m64 decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
140
141 /* Form branch metrics
142 * Because Branchtab takes on values 0 and 255, and the values of sym?v are offset binary in the range 0-255,
143 * the XOR operations constitute conditional negation.
144 * metric and m_metric (-metric) are in the range 0-765
145 */
146 m0 = _mm_add_pi16(_mm_xor_si64(Branchtab39[0].v[i],sym0v),_mm_xor_si64(Branchtab39[1].v[i],sym1v));
147 metric = _mm_add_pi16(_mm_xor_si64(Branchtab39[2].v[i],sym2v),m0);
148 m_metric = _mm_sub_pi16(_mm_set1_pi16(765),metric);
149
150 /* Add branch metrics to path metrics */
151 m0 = _mm_adds_pi16(vp->old_metrics->v[i],metric);
152 m3 = _mm_adds_pi16(vp->old_metrics->v[32+i],metric);
153 m1 = _mm_adds_pi16(vp->old_metrics->v[32+i],m_metric);
154 m2 = _mm_adds_pi16(vp->old_metrics->v[i],m_metric);
155
156 /* Compare and select */
157 survivor0 = _mm_min_pi16(m0,m1);
158 survivor1 = _mm_min_pi16(m2,m3);
159 decision0 = _mm_cmpeq_pi16(survivor0,m1);
160 decision1 = _mm_cmpeq_pi16(survivor1,m3);
161
162 /* Pack decisions into 8 bits and store */
163 d->c[i] = _mm_movemask_pi8(_mm_unpacklo_pi8(_mm_packs_pi16(decision0,_mm_setzero_si64()),_mm_packs_pi16(decision1,_mm_setzero_si64())));
164
165 /* Store surviving metrics */
166 vp->new_metrics->v[2*i] = _mm_unpacklo_pi16(survivor0,survivor1);
167 vp->new_metrics->v[2*i+1] = _mm_unpackhi_pi16(survivor0,survivor1);
168 }
169 /* See if we need to renormalize
170 * Max metric spread for this code with 0-255 branch metrics is 12750
171 */
172 if(vp->new_metrics->s[0] >= SHRT_MAX-5000){
173 int i,adjust;
174 __m64 adjustv;
175 union { __m64 v; signed short w[4]; } t;
176
177 /* Find smallest metric and set adjustv to bring it down to SHRT_MIN */
178 adjustv = vp->new_metrics->v[0];
179 for(i=1;i<64;i++)
180 adjustv = _mm_min_pi16(adjustv,vp->new_metrics->v[i]);
181
182 adjustv = _mm_min_pi16(adjustv,_mm_srli_si64(adjustv,32));
183 adjustv = _mm_min_pi16(adjustv,_mm_srli_si64(adjustv,16));
184 t.v = adjustv;
185 adjust = t.w[0] - SHRT_MIN;
186 path_metric += adjust;
187 adjustv = _mm_set1_pi16(adjust);
188
189 for(i=0;i<64;i++)
190 vp->new_metrics->v[i] = _mm_sub_pi16(vp->new_metrics->v[i],adjustv);
191 }
192 d++;
193 /* Swap pointers to old and new metrics */
194 tmp = vp->old_metrics;
195 vp->old_metrics = vp->new_metrics;
196 vp->new_metrics = tmp;
197 }
198 vp->dp = d;
199 _mm_empty();
200 return path_metric;
201 }
202