1 /* K=15 r=1/6 Viterbi decoder for x86 SSE
2 * Copyright Mar 2004, 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[512]; unsigned char c[2048];} decision_t;
13 typedef union { signed short s[16384]; __m64 v[4096];} metric_t;
14
15 static union branchtab615 { unsigned short s[8192]; __m64 v[2048];} Branchtab615[6];
16 static int Init = 0;
17
18 /* State info for instance of Viterbi decoder */
19 struct v615 {
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_viterbi615_sse(void * p,int starting_state)28 int init_viterbi615_sse(void *p,int starting_state){
29 struct v615 *vp = p;
30 int i;
31
32 if(p == NULL)
33 return -1;
34 for(i=0;i<16384;i++)
35 vp->metrics1.s[i] = (SHRT_MIN+5000);
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 & 16383] = SHRT_MIN; /* Bias known start state */
41 return 0;
42 }
43
44 /* Create a new instance of a Viterbi decoder */
create_viterbi615_sse(int len)45 void *create_viterbi615_sse(int len){
46 struct v615 *vp;
47
48 if(!Init){
49 int polys[6] = { V615POLYA,V615POLYB,V615POLYC,V615POLYD,V615POLYE,V615POLYF };
50 set_viterbi615_polynomial_sse(polys);
51 }
52
53 if((vp = (struct v615 *)malloc(sizeof(struct v615))) == NULL){
54 return NULL;
55 }
56 if((vp->decisions = malloc((len+14)*sizeof(decision_t))) == NULL){
57 free(vp);
58 return NULL;
59 }
60 init_viterbi615_sse(vp,0);
61 return vp;
62 }
63
set_viterbi615_polynomial_sse(int polys[6])64 void set_viterbi615_polynomial_sse(int polys[6]){
65 int state;
66 int i;
67
68 for(state=0;state < 8192;state++){
69 for(i=0;i<6;i++)
70 Branchtab615[i].s[state] = (polys[i] < 0) ^ parity((2*state) & abs(polys[i])) ? 255 : 0;
71 }
72 Init++;
73 }
74
75 /* Viterbi chainback */
chainback_viterbi615_sse(void * p,unsigned char * data,unsigned int nbits,unsigned int endstate)76 int chainback_viterbi615_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 v615 *vp = p;
82 decision_t *d;
83
84 if(p == NULL)
85 return -1;
86 d = (decision_t *)vp->decisions;
87 endstate %= 16384;
88
89 /* The store into data[] only needs to be done every 8 bits.
90 * But this avoids a conditional branch, and the writes will
91 * combine in the cache anyway
92 */
93 d += 14; /* Look past tail */
94 while(nbits-- != 0){
95 int k;
96
97 /* k = (d[nbits].w[endstate/32] >> (endstate%32)) & 1;*/
98 k = (d[nbits].c[endstate/8] >> (endstate%8)) & 1;
99 endstate = (k << 13) | (endstate >> 1);
100 data[nbits>>3] = endstate >> 6;
101 }
102 return 0;
103 }
104
105 /* Delete instance of a Viterbi decoder */
delete_viterbi615_sse(void * p)106 void delete_viterbi615_sse(void *p){
107 struct v615 *vp = p;
108
109 if(vp != NULL){
110 free(vp->decisions);
111 free(vp);
112 }
113 }
114
115
update_viterbi615_blk_sse(void * p,unsigned char * syms,int nbits)116 int update_viterbi615_blk_sse(void *p,unsigned char *syms,int nbits){
117 struct v615 *vp = p;
118 decision_t *d;
119
120 if(p == NULL)
121 return -1;
122 d = (decision_t *)vp->dp;
123 while(nbits--){
124 __m64 sym0v,sym1v,sym2v,sym3v,sym4v,sym5v;
125 void *tmp;
126 int i;
127
128 /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */
129 sym0v = _mm_set1_pi16(syms[0]);
130 sym1v = _mm_set1_pi16(syms[1]);
131 sym2v = _mm_set1_pi16(syms[2]);
132 sym3v = _mm_set1_pi16(syms[3]);
133 sym4v = _mm_set1_pi16(syms[4]);
134 sym5v = _mm_set1_pi16(syms[5]);
135 syms += 6;
136
137 for(i=0;i<2048;i++){
138 __m64 decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
139
140 /* Form branch metrics
141 * Because Branchtab takes on values 0 and 255, and the values of sym?v are offset binary in the range 0-255,
142 * the XOR operations constitute conditional negation.
143 * metric and m_metric (-metric) are in the range 0-1530
144 */
145 m0 = _mm_add_pi16(_mm_xor_si64(Branchtab615[0].v[i],sym0v),_mm_xor_si64(Branchtab615[1].v[i],sym1v));
146 m1 = _mm_add_pi16(_mm_xor_si64(Branchtab615[2].v[i],sym2v),_mm_xor_si64(Branchtab615[3].v[i],sym3v));
147 m2 = _mm_add_pi16(_mm_xor_si64(Branchtab615[4].v[i],sym4v),_mm_xor_si64(Branchtab615[5].v[i],sym5v));
148 metric = _mm_add_pi16(m0,_mm_add_pi16(m1,m2));
149 m_metric = _mm_sub_pi16(_mm_set1_pi16(1530),metric);
150
151 /* Add branch metrics to path metrics */
152 m0 = _mm_adds_pi16(vp->old_metrics->v[i],metric);
153 m3 = _mm_adds_pi16(vp->old_metrics->v[2048+i],metric);
154 m1 = _mm_adds_pi16(vp->old_metrics->v[2048+i],m_metric);
155 m2 = _mm_adds_pi16(vp->old_metrics->v[i],m_metric);
156
157 /* Compare and select */
158 survivor0 = _mm_min_pi16(m0,m1);
159 survivor1 = _mm_min_pi16(m2,m3);
160 decision0 = _mm_cmpeq_pi16(survivor0,m1);
161 decision1 = _mm_cmpeq_pi16(survivor1,m3);
162
163 /* Pack decisions into 8 bits and store */
164 d->c[i] = _mm_movemask_pi8(_mm_unpacklo_pi8(_mm_packs_pi16(decision0,_mm_setzero_si64()),_mm_packs_pi16(decision1,_mm_setzero_si64())));
165
166 /* Store surviving metrics */
167 vp->new_metrics->v[2*i] = _mm_unpacklo_pi16(survivor0,survivor1);
168 vp->new_metrics->v[2*i+1] = _mm_unpackhi_pi16(survivor0,survivor1);
169 }
170 /* See if we need to renormalize
171 * Max metric spread for this code with 0-255 branch metrics is 12750
172 */
173 if(vp->new_metrics->s[0] >= SHRT_MAX-12750){
174 int i,adjust;
175 __m64 adjustv;
176 union { __m64 v; signed short w[4]; } t;
177
178 /* Find smallest metric and set adjustv to bring it down to SHRT_MIN */
179 adjustv = vp->new_metrics->v[0];
180 for(i=1;i<4096;i++)
181 adjustv = _mm_min_pi16(adjustv,vp->new_metrics->v[i]);
182
183 adjustv = _mm_min_pi16(adjustv,_mm_srli_si64(adjustv,32));
184 adjustv = _mm_min_pi16(adjustv,_mm_srli_si64(adjustv,16));
185 t.v = adjustv;
186 adjust = t.w[0] - SHRT_MIN;
187 adjustv = _mm_set1_pi16(adjust);
188
189 for(i=0;i<4096;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 0;
201 }
202