1 /* K=7 r=1/2 Viterbi decoder for PowerPC G4/G5 Altivec instructions
2 * Feb 2004, Phil Karn, KA9Q
3 */
4 #include <stdio.h>
5 #include <memory.h>
6 #include <stdlib.h>
7 #include "fec.h"
8
9 typedef union { long long p; unsigned char c[64]; vector bool char v[4]; } decision_t;
10 typedef union { long long p; unsigned char c[64]; vector unsigned char v[4]; } metric_t;
11
12 static union branchtab27 { unsigned char c[32]; vector unsigned char v[2];} Branchtab27[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 [mmx|sse|sse2]bfly29.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 /* Initialize Viterbi decoder for start of new frame */
init_viterbi27_av(void * p,int starting_state)27 int init_viterbi27_av(void *p,int starting_state){
28 struct v27 *vp = p;
29 int i;
30
31 if(p == NULL)
32 return -1;
33 for(i=0;i<4;i++)
34 vp->metrics1.v[i] = (vector unsigned char)(63);
35 vp->old_metrics = &vp->metrics1;
36 vp->new_metrics = &vp->metrics2;
37 vp->dp = vp->decisions;
38 vp->old_metrics->c[starting_state & 63] = 0; /* Bias known start state */
39 return 0;
40 }
41
set_viterbi27_polynomial_av(int polys[2])42 void set_viterbi27_polynomial_av(int polys[2]){
43 int state;
44
45 for(state=0;state < 32;state++){
46 Branchtab27[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
47 Branchtab27[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
48 }
49 Init++;
50 }
51
52 /* Create a new instance of a Viterbi decoder */
create_viterbi27_av(int len)53 void *create_viterbi27_av(int len){
54 struct v27 *vp;
55
56 if(!Init){
57 int polys[2] = { V27POLYA,V27POLYB };
58 set_viterbi27_polynomial_av(polys);
59 }
60 if((vp = (struct v27 *)malloc(sizeof(struct v27))) == NULL)
61 return NULL;
62 if((vp->decisions = (decision_t *)malloc((len+6)*sizeof(decision_t))) == NULL){
63 free(vp);
64 return NULL;
65 }
66 init_viterbi27_av(vp,0);
67 return vp;
68 }
69
70 /* Viterbi chainback */
chainback_viterbi27_av(void * p,unsigned char * data,unsigned int nbits,unsigned int endstate)71 int chainback_viterbi27_av(
72 void *p,
73 unsigned char *data, /* Decoded output data */
74 unsigned int nbits, /* Number of data bits */
75 unsigned int endstate){ /* Terminal encoder state */
76 struct v27 *vp = p;
77 decision_t *d = (decision_t *)vp->decisions;
78
79 if(p == NULL)
80 return -1;
81
82 /* Make room beyond the end of the encoder register so we can
83 * accumulate a full byte of decoded data
84 */
85 endstate %= 64;
86 endstate <<= 2;
87
88 /* The store into data[] only needs to be done every 8 bits.
89 * But this avoids a conditional branch, and the writes will
90 * combine in the cache anyway
91 */
92 d += 6; /* Look past tail */
93 while(nbits-- != 0){
94 int k;
95
96 k = d[nbits].c[endstate>>2] & 1;
97 data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
98 }
99 return 0;
100 }
101
102 /* Delete instance of a Viterbi decoder */
delete_viterbi27_av(void * p)103 void delete_viterbi27_av(void *p){
104 struct v27 *vp = p;
105
106 if(vp != NULL){
107 free(vp->decisions);
108 free(vp);
109 }
110 }
111
112 /* Process received symbols */
update_viterbi27_blk_av(void * p,unsigned char * syms,int nbits)113 int update_viterbi27_blk_av(void *p,unsigned char *syms,int nbits){
114 struct v27 *vp = p;
115 decision_t *d;
116
117 if(p == NULL)
118 return -1;
119 d = (decision_t *)vp->dp;
120 while(nbits--){
121 vector unsigned char survivor0,survivor1,sym0v,sym1v;
122 vector bool char decision0,decision1;
123 vector unsigned char metric,m_metric,m0,m1,m2,m3;
124 void *tmp;
125
126 /* sym0v.0 = syms[0]; sym0v.1 = syms[1] */
127 sym0v = vec_perm(vec_ld(0,syms),vec_ld(1,syms),vec_lvsl(0,syms));
128
129 sym1v = vec_splat(sym0v,1); /* Splat syms[1] across sym1v */
130 sym0v = vec_splat(sym0v,0); /* Splat syms[0] across sym0v */
131 syms += 2;
132
133 /* Do the 32 butterflies as two interleaved groups of 16 each to keep the pipes full */
134
135 /* Form first set of 16 branch metrics */
136 metric = vec_avg(vec_xor(Branchtab27[0].v[0],sym0v),vec_xor(Branchtab27[1].v[0],sym1v));
137 metric = vec_sr(metric,(vector unsigned char)(3));
138 m_metric = vec_sub((vector unsigned char)(31),metric);
139
140 /* Form first set of path metrics */
141 m0 = vec_adds(vp->old_metrics->v[0],metric);
142 m3 = vec_adds(vp->old_metrics->v[2],metric);
143 m1 = vec_adds(vp->old_metrics->v[2],m_metric);
144 m2 = vec_adds(vp->old_metrics->v[0],m_metric);
145
146 /* Form second set of 16 branch metrics */
147 metric = vec_avg(vec_xor(Branchtab27[0].v[1],sym0v),vec_xor(Branchtab27[1].v[1],sym1v));
148 metric = vec_sr(metric,(vector unsigned char)(3));
149 m_metric = vec_sub((vector unsigned char)(31),metric);
150
151 /* Compare and select first set */
152 decision0 = vec_cmpgt(m0,m1);
153 decision1 = vec_cmpgt(m2,m3);
154 survivor0 = vec_min(m0,m1);
155 survivor1 = vec_min(m2,m3);
156
157 /* Compute second set of path metrics */
158 m0 = vec_adds(vp->old_metrics->v[1],metric);
159 m3 = vec_adds(vp->old_metrics->v[3],metric);
160 m1 = vec_adds(vp->old_metrics->v[3],m_metric);
161 m2 = vec_adds(vp->old_metrics->v[1],m_metric);
162
163 /* Interleave and store first decisions and survivors */
164 d->v[0] = vec_mergeh(decision0,decision1);
165 d->v[1] = vec_mergel(decision0,decision1);
166 vp->new_metrics->v[0] = vec_mergeh(survivor0,survivor1);
167 vp->new_metrics->v[1] = vec_mergel(survivor0,survivor1);
168
169 /* Compare and select second set */
170 decision0 = vec_cmpgt(m0,m1);
171 decision1 = vec_cmpgt(m2,m3);
172 survivor0 = vec_min(m0,m1);
173 survivor1 = vec_min(m2,m3);
174
175 /* Interleave and store second set of decisions and survivors */
176 d->v[2] = vec_mergeh(decision0,decision1);
177 d->v[3] = vec_mergel(decision0,decision1);
178 vp->new_metrics->v[2] = vec_mergeh(survivor0,survivor1);
179 vp->new_metrics->v[3] = vec_mergel(survivor0,survivor1);
180
181 /* renormalize if necessary */
182 if(vp->new_metrics->c[0] >= 105){
183 vector unsigned char scale0,scale1;
184
185 /* Find smallest metric and splat */
186 scale0 = vec_min(vp->new_metrics->v[0],vp->new_metrics->v[1]);
187 scale1 = vec_min(vp->new_metrics->v[2],vp->new_metrics->v[3]);
188 scale0 = vec_min(scale0,scale1);
189 scale0 = vec_min(scale0,vec_sld(scale0,scale0,8));
190 scale0 = vec_min(scale0,vec_sld(scale0,scale0,4));
191 scale0 = vec_min(scale0,vec_sld(scale0,scale0,2));
192 scale0 = vec_min(scale0,vec_sld(scale0,scale0,1));
193
194 /* Now subtract from all metrics */
195 vp->new_metrics->v[0] = vec_subs(vp->new_metrics->v[0],scale0);
196 vp->new_metrics->v[1] = vec_subs(vp->new_metrics->v[1],scale0);
197 vp->new_metrics->v[2] = vec_subs(vp->new_metrics->v[2],scale0);
198 vp->new_metrics->v[3] = vec_subs(vp->new_metrics->v[3],scale0);
199 }
200 d++;
201 /* Swap pointers to old and new metrics */
202 tmp = vp->old_metrics;
203 vp->old_metrics = vp->new_metrics;
204 vp->new_metrics = tmp;
205 }
206 vp->dp = d;
207
208 return 0;
209 }
210
211