Bill Yi | 4e213d5 | 2015-06-23 13:53:11 -0700 | [diff] [blame] | 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 | |
| 11 | typedef union { unsigned char c[256]; vector bool char v[16]; } decision_t; |
| 12 | typedef union { unsigned char c[256]; vector unsigned char v[16]; } metric_t; |
| 13 | |
| 14 | static union branchtab29 { unsigned char c[128]; vector unsigned char v[8]; } Branchtab29[2]; |
| 15 | static int Init = 0; |
| 16 | |
| 17 | /* State info for instance of Viterbi decoder */ |
| 18 | struct 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 */ |
| 27 | int 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 | |
| 43 | void 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 */ |
| 54 | void *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 */ |
| 72 | int 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 */ |
| 104 | void 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 | |
| 114 | int 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 | } |