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