1 /* K=9 r=1/2 Viterbi decoder for PowerPC G4/G5 Altivec
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 <altivec.h>
6 #include <stdio.h>
7 #include <stdlib.h>
8 #include <memory.h>
9 #include <sys/types.h>
10 #include <sys/sysctl.h>
11 #include "fec.h"
12
13 typedef union { unsigned char c[256]; vector bool char v[16]; } decision_t;
14 typedef union { unsigned char c[256]; vector unsigned char v[16]; } metric_t;
15
16 static union branchtab29 { unsigned char c[128]; vector unsigned char v[8]; } Branchtab29[2];
17 static int Init = 0;
18
19 /* State info for instance of Viterbi decoder */
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_av(void * p,int starting_state)29 int init_viterbi29_av(void *p,int starting_state){
30 struct v29 *vp = p;
31 int i;
32
33 if(p == NULL)
34 return -1;
35 for(i=0;i<16;i++)
36 vp->metrics1.v[i] = (vector unsigned char){63};
37
38 vp->old_metrics = &vp->metrics1;
39 vp->new_metrics = &vp->metrics2;
40 vp->dp = vp->decisions;
41 vp->old_metrics->c[starting_state & 255] = 0; /* Bias known start state */
42 return 0;
43 }
44
set_viterbi29_polynomial_av(int polys[2])45 void set_viterbi29_polynomial_av(int polys[2]){
46 int state;
47
48 for(state=0;state < 128;state++){
49 Branchtab29[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
50 Branchtab29[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
51 }
52 Init++;
53 }
54
55 /* Create a new instance of a Viterbi decoder */
create_viterbi29_av(int len)56 void *create_viterbi29_av(int len){
57 struct v29 *vp;
58
59 if(!Init){
60 int polys[2] = { V29POLYA,V29POLYB };
61 set_viterbi29_polynomial_av(polys);
62 }
63 if((vp = (struct v29 *)malloc(sizeof(struct v29))) == NULL)
64 return NULL;
65 if((vp->decisions = (decision_t *)malloc((len+8)*sizeof(decision_t))) == NULL){
66 free(vp);
67 return NULL;
68 }
69 init_viterbi29_av(vp,0);
70 return vp;
71 }
72
73 /* Viterbi chainback */
chainback_viterbi29_av(void * p,unsigned char * data,unsigned int nbits,unsigned int endstate)74 int chainback_viterbi29_av(
75 void *p,
76 unsigned char *data, /* Decoded output data */
77 unsigned int nbits, /* Number of data bits */
78 unsigned int endstate){ /* Terminal encoder state */
79 struct v29 *vp = p;
80 decision_t *d;
81
82 if(p == NULL)
83 return -1;
84 d = (decision_t *)vp->decisions;
85 /* Make room beyond the end of the encoder register so we can
86 * accumulate a full byte of decoded data
87 */
88 endstate %= 256;
89
90 /* The store into data[] only needs to be done every 8 bits.
91 * But this avoids a conditional branch, and the writes will
92 * combine in the cache anyway
93 */
94 d += 8; /* Look past tail */
95 while(nbits-- != 0){
96 int k;
97
98 k = d[nbits].c[endstate] & 1;
99 data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
100 }
101 return 0;
102 }
103
104
105 /* Delete instance of a Viterbi decoder */
delete_viterbi29_av(void * p)106 void delete_viterbi29_av(void *p){
107 struct v29 *vp = p;
108
109 if(vp != NULL){
110 free(vp->decisions);
111 free(vp);
112 }
113 }
114
115
update_viterbi29_blk_av(void * p,unsigned char * syms,int nbits)116 int update_viterbi29_blk_av(void *p,unsigned char *syms,int nbits){
117 struct v29 *vp = p;
118 decision_t *d;
119 int i;
120
121 if(p == NULL)
122 return -1;
123 d = (decision_t *)vp->dp;
124
125 while(nbits--){
126 vector unsigned char sym1v,sym2v;
127 void *tmp;
128
129 /* All this seems necessary just to load a byte into all elements of a vector! */
130 sym1v = vec_perm(vec_ld(0,syms),vec_ld(1,syms),vec_lvsl(0,syms)); /* sym1v.0 = syms[0]; sym1v.1 = syms[1] */
131 sym2v = vec_splat(sym1v,1); /* Splat syms[1] across sym2v */
132 sym1v = vec_splat(sym1v,0); /* Splat syms[0] across sym1v */
133 syms += 2;
134
135 for(i=0;i<8;i++){
136 vector bool char decision0,decision1;
137 vector unsigned char metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
138
139 /* Form branch metrics */
140 metric = vec_avg(vec_xor(Branchtab29[0].v[i],sym1v),vec_xor(Branchtab29[1].v[i],sym2v));
141 metric = vec_sr(metric,(vector unsigned char){3});
142 m_metric = (vector unsigned char){31} - metric;
143
144 /* Add branch metrics to path metrics */
145 m0 = vec_adds(vp->old_metrics->v[i],metric);
146 m3 = vec_adds(vp->old_metrics->v[8+i],metric);
147 m1 = vec_adds(vp->old_metrics->v[8+i],m_metric);
148 m2 = vec_adds(vp->old_metrics->v[i],m_metric);
149
150 /* Compare and select first set */
151 decision0 = vec_cmpgt(m0,m1);
152 decision1 = vec_cmpgt(m2,m3);
153 survivor0 = vec_min(m0,m1);
154 survivor1 = vec_min(m2,m3);
155
156 /* Interleave and store decisions and survivors */
157 d->v[2*i] = vec_mergeh(decision0,decision1);
158 d->v[2*i+1] = vec_mergel(decision0,decision1);
159 vp->new_metrics->v[2*i] = vec_mergeh(survivor0,survivor1);
160 vp->new_metrics->v[2*i+1] = vec_mergel(survivor0,survivor1);
161 }
162 d++;
163 /* renormalize if necessary */
164 if(vp->new_metrics->c[0] >= 50){
165 int i;
166 vector unsigned char scale0,scale1;
167
168 /* Find smallest metric and splat */
169 scale0 = vp->new_metrics->v[0];
170 scale1 = vp->new_metrics->v[1];
171 for(i=2;i<16;i+=2){
172 scale0 = vec_min(scale0,vp->new_metrics->v[i]);
173 scale1 = vec_min(scale1,vp->new_metrics->v[i+1]);
174 }
175 scale0 = vec_min(scale0,scale1);
176 scale0 = vec_min(scale0,vec_sld(scale0,scale0,8));
177 scale0 = vec_min(scale0,vec_sld(scale0,scale0,4));
178 scale0 = vec_min(scale0,vec_sld(scale0,scale0,2));
179 scale0 = vec_min(scale0,vec_sld(scale0,scale0,1));
180
181 /* Now subtract from all metrics */
182 for(i=0;i<16;i++)
183 vp->new_metrics->v[i] = vec_subs(vp->new_metrics->v[i],scale0);
184 }
185 /* Swap pointers to old and new metrics */
186 tmp = vp->old_metrics;
187 vp->old_metrics = vp->new_metrics;
188 vp->new_metrics = tmp;
189 }
190 vp->dp = d;
191 return 0;
192 }
193