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 <stdio.h>
6#include <stdlib.h>
7#include <memory.h>
8#include <sys/sysctl.h>
9#include "fec.h"
10
11typedef union { unsigned char c[256]; vector bool char v[16]; } decision_t;
12typedef union { unsigned char c[256]; vector unsigned char v[16]; } metric_t;
13
14static union branchtab29 { unsigned char c[128]; vector unsigned char v[8]; } Branchtab29[2];
15static int Init = 0;
16
17/* State info for instance of Viterbi decoder */
18struct v29 {
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 */
27int init_viterbi29_av(void *p,int starting_state){
28  struct v29 *vp = p;
29  int i;
30
31  if(p == NULL)
32    return -1;
33  for(i=0;i<16;i++)
34    vp->metrics1.v[i] = (vector unsigned char)(63);
35
36  vp->old_metrics = &vp->metrics1;
37  vp->new_metrics = &vp->metrics2;
38  vp->dp = vp->decisions;
39  vp->old_metrics->c[starting_state & 255] = 0; /* Bias known start state */
40  return 0;
41}
42
43void set_viterbi29_polynomial_av(int polys[2]){
44  int state;
45
46  for(state=0;state < 128;state++){
47    Branchtab29[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
48    Branchtab29[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
49  }
50  Init++;
51}
52
53/* Create a new instance of a Viterbi decoder */
54void *create_viterbi29_av(int len){
55  struct v29 *vp;
56
57  if(!Init){
58    int polys[2] = { V29POLYA,V29POLYB };
59    set_viterbi29_polynomial_av(polys);
60  }
61  if((vp = (struct v29 *)malloc(sizeof(struct v29))) == NULL)
62    return NULL;
63  if((vp->decisions = (decision_t *)malloc((len+8)*sizeof(decision_t))) == NULL){
64    free(vp);
65    return NULL;
66  }
67  init_viterbi29_av(vp,0);
68  return vp;
69}
70
71/* Viterbi chainback */
72int chainback_viterbi29_av(
73      void *p,
74      unsigned char *data, /* Decoded output data */
75      unsigned int nbits, /* Number of data bits */
76      unsigned int endstate){ /* Terminal encoder state */
77  struct v29 *vp = p;
78  decision_t *d;
79
80  if(p == NULL)
81    return -1;
82  d = (decision_t *)vp->decisions;
83  /* Make room beyond the end of the encoder register so we can
84   * accumulate a full byte of decoded data
85   */
86  endstate %= 256;
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 += 8; /* Look past tail */
93  while(nbits-- != 0){
94    int k;
95
96    k = d[nbits].c[endstate] & 1;
97    data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
98  }
99  return 0;
100}
101
102
103/* Delete instance of a Viterbi decoder */
104void delete_viterbi29_av(void *p){
105  struct v29 *vp = p;
106
107  if(vp != NULL){
108    free(vp->decisions);
109    free(vp);
110  }
111}
112
113
114int update_viterbi29_blk_av(void *p,unsigned char *syms,int nbits){
115  struct v29 *vp = p;
116  decision_t *d;
117  int i;
118
119  if(p == NULL)
120    return -1;
121  d = (decision_t *)vp->dp;
122
123  while(nbits--){
124    vector unsigned char sym1v,sym2v;
125    void *tmp;
126
127    /* All this seems necessary just to load a byte into all elements of a vector! */
128    sym1v = vec_perm(vec_ld(0,syms),vec_ld(1,syms),vec_lvsl(0,syms)); /* sym1v.0 = syms[0]; sym1v.1 = syms[1] */
129    sym2v = vec_splat(sym1v,1); /* Splat syms[1] across sym2v */
130    sym1v = vec_splat(sym1v,0); /* Splat syms[0] across sym1v */
131    syms += 2;
132
133    for(i=0;i<8;i++){
134      vector bool char decision0,decision1;
135      vector unsigned char metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
136
137      /* Form branch metrics */
138      metric = vec_avg(vec_xor(Branchtab29[0].v[i],sym1v),vec_xor(Branchtab29[1].v[i],sym2v));
139      metric = vec_sr(metric,(vector unsigned char)(3));
140      m_metric = (vector unsigned char)(31) - metric;
141
142      /* Add branch metrics to path metrics */
143      m0 = vec_adds(vp->old_metrics->v[i],metric);
144      m3 = vec_adds(vp->old_metrics->v[8+i],metric);
145      m1 = vec_adds(vp->old_metrics->v[8+i],m_metric);
146      m2 = vec_adds(vp->old_metrics->v[i],m_metric);
147
148      /* Compare and select first set */
149      decision0 = vec_cmpgt(m0,m1);
150      decision1 = vec_cmpgt(m2,m3);
151      survivor0 = vec_min(m0,m1);
152      survivor1 = vec_min(m2,m3);
153
154      /* Interleave and store decisions and survivors */
155      d->v[2*i] = vec_mergeh(decision0,decision1);
156      d->v[2*i+1] = vec_mergel(decision0,decision1);
157      vp->new_metrics->v[2*i] = vec_mergeh(survivor0,survivor1);
158      vp->new_metrics->v[2*i+1] = vec_mergel(survivor0,survivor1);
159    }
160    d++;
161    /* renormalize if necessary */
162    if(vp->new_metrics->c[0] >= 50){
163      int i;
164      vector unsigned char scale0,scale1;
165
166      /* Find smallest metric and splat */
167      scale0 = vp->new_metrics->v[0];
168      scale1 = vp->new_metrics->v[1];
169      for(i=2;i<16;i+=2){
170	scale0 = vec_min(scale0,vp->new_metrics->v[i]);
171	scale1 = vec_min(scale1,vp->new_metrics->v[i+1]);
172      }
173      scale0 = vec_min(scale0,scale1);
174      scale0 = vec_min(scale0,vec_sld(scale0,scale0,8));
175      scale0 = vec_min(scale0,vec_sld(scale0,scale0,4));
176      scale0 = vec_min(scale0,vec_sld(scale0,scale0,2));
177      scale0 = vec_min(scale0,vec_sld(scale0,scale0,1));
178
179      /* Now subtract from all metrics */
180      for(i=0;i<16;i++)
181	vp->new_metrics->v[i] = vec_subs(vp->new_metrics->v[i],scale0);
182    }
183    /* Swap pointers to old and new metrics */
184    tmp = vp->old_metrics;
185    vp->old_metrics = vp->new_metrics;
186    vp->new_metrics = tmp;
187  }
188  vp->dp = d;
189  return 0;
190}
191