Bill Yi | 4e213d5 | 2015-06-23 13:53:11 -0700 | [diff] [blame] | 1 | /* K=9 r=1/3 Viterbi decoder in portable C |
| 2 | * Copyright Aug 2006, 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 "fec.h" |
| 9 | |
| 10 | typedef union { unsigned int w[256]; } metric_t; |
| 11 | typedef union { unsigned long w[8];} decision_t; |
| 12 | |
| 13 | static union { unsigned char c[128]; } Branchtab39[3]; |
| 14 | static int Init = 0; |
| 15 | |
| 16 | /* State info for instance of Viterbi decoder */ |
| 17 | struct v39 { |
| 18 | metric_t metrics1; /* path metric buffer 1 */ |
| 19 | metric_t metrics2; /* path metric buffer 2 */ |
| 20 | decision_t *dp; /* Pointer to current decision */ |
| 21 | metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */ |
| 22 | decision_t *decisions; /* Beginning of decisions for block */ |
| 23 | }; |
| 24 | |
| 25 | /* Initialize Viterbi decoder for start of new frame */ |
| 26 | int init_viterbi39_port(void *p,int starting_state){ |
| 27 | struct v39 *vp = p; |
| 28 | int i; |
| 29 | |
| 30 | if(p == NULL) |
| 31 | return -1; |
| 32 | for(i=0;i<256;i++) |
| 33 | vp->metrics1.w[i] = 63; |
| 34 | |
| 35 | vp->old_metrics = &vp->metrics1; |
| 36 | vp->new_metrics = &vp->metrics2; |
| 37 | vp->dp = vp->decisions; |
| 38 | vp->old_metrics->w[starting_state & 255] = 0; /* Bias known start state */ |
| 39 | return 0; |
| 40 | } |
| 41 | |
| 42 | void set_viterbi39_polynomial_port(int polys[3]){ |
| 43 | int state; |
| 44 | |
| 45 | for(state=0;state < 128;state++){ |
| 46 | Branchtab39[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0; |
| 47 | Branchtab39[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0; |
| 48 | Branchtab39[2].c[state] = (polys[2] < 0) ^ parity((2*state) & abs(polys[2])) ? 255 : 0; |
| 49 | } |
| 50 | Init++; |
| 51 | } |
| 52 | |
| 53 | /* Create a new instance of a Viterbi decoder */ |
| 54 | void *create_viterbi39_port(int len){ |
| 55 | struct v39 *vp; |
| 56 | |
| 57 | if(!Init){ |
| 58 | int polys[3] = {V39POLYA,V39POLYB,V39POLYC}; |
| 59 | set_viterbi39_polynomial_port(polys); |
| 60 | } |
| 61 | if((vp = (struct v39 *)malloc(sizeof(struct v39))) == NULL) |
| 62 | return NULL; |
| 63 | |
| 64 | if((vp->decisions = (decision_t *)malloc((len+8)*sizeof(decision_t))) == NULL){ |
| 65 | free(vp); |
| 66 | return NULL; |
| 67 | } |
| 68 | init_viterbi39_port(vp,0); |
| 69 | |
| 70 | return vp; |
| 71 | } |
| 72 | |
| 73 | |
| 74 | /* Viterbi chainback */ |
| 75 | int chainback_viterbi39_port( |
| 76 | void *p, |
| 77 | unsigned char *data, /* Decoded output data */ |
| 78 | unsigned int nbits, /* Number of data bits */ |
| 79 | unsigned int endstate){ /* Terminal encoder state */ |
| 80 | struct v39 *vp = p; |
| 81 | decision_t *d; |
| 82 | |
| 83 | if(p == NULL) |
| 84 | return -1; |
| 85 | |
| 86 | d = vp->decisions; |
| 87 | /* Make room beyond the end of the encoder register so we can |
| 88 | * accumulate a full byte of decoded data |
| 89 | */ |
| 90 | endstate %= 256; |
| 91 | |
| 92 | /* The store into data[] only needs to be done every 8 bits. |
| 93 | * But this avoids a conditional branch, and the writes will |
| 94 | * combine in the cache anyway |
| 95 | */ |
| 96 | d += 8; /* Look past tail */ |
| 97 | while(nbits-- != 0){ |
| 98 | int k; |
| 99 | |
| 100 | k = (d[nbits].w[(endstate)/32] >> (endstate%32)) & 1; |
| 101 | data[nbits>>3] = endstate = (endstate >> 1) | (k << 7); |
| 102 | } |
| 103 | return 0; |
| 104 | } |
| 105 | |
| 106 | |
| 107 | /* Delete instance of a Viterbi decoder */ |
| 108 | void delete_viterbi39_port(void *p){ |
| 109 | struct v39 *vp = p; |
| 110 | |
| 111 | if(vp != NULL){ |
| 112 | free(vp->decisions); |
| 113 | free(vp); |
| 114 | } |
| 115 | } |
| 116 | |
| 117 | /* C-language butterfly */ |
| 118 | #define BFLY(i) {\ |
| 119 | unsigned int metric,m0,m1,decision;\ |
| 120 | metric = (Branchtab39[0].c[i] ^ sym0) + (Branchtab39[1].c[i] ^ sym1) + \ |
| 121 | (Branchtab39[2].c[i] ^ sym2);\ |
| 122 | m0 = vp->old_metrics->w[i] + metric;\ |
| 123 | m1 = vp->old_metrics->w[i+128] + (765 - metric);\ |
| 124 | decision = (signed int)(m0-m1) > 0;\ |
| 125 | vp->new_metrics->w[2*i] = decision ? m1 : m0;\ |
| 126 | d->w[i/16] |= decision << ((2*i)&31);\ |
| 127 | m0 -= (metric+metric-765);\ |
| 128 | m1 += (metric+metric-765);\ |
| 129 | decision = (signed int)(m0-m1) > 0;\ |
| 130 | vp->new_metrics->w[2*i+1] = decision ? m1 : m0;\ |
| 131 | d->w[i/16] |= decision << ((2*i+1)&31);\ |
| 132 | } |
| 133 | |
| 134 | /* Update decoder with a block of demodulated symbols |
| 135 | * Note that nbits is the number of decoded data bits, not the number |
| 136 | * of symbols! |
| 137 | */ |
| 138 | |
| 139 | int update_viterbi39_blk_port(void *p,unsigned char *syms,int nbits){ |
| 140 | struct v39 *vp = p; |
| 141 | decision_t *d; |
| 142 | |
| 143 | if(p == NULL) |
| 144 | return -1; |
| 145 | |
| 146 | d = (decision_t *)vp->dp; |
| 147 | while(nbits--){ |
| 148 | void *tmp; |
| 149 | unsigned char sym0,sym1,sym2; |
| 150 | int i; |
| 151 | |
| 152 | for(i=0;i<8;i++) |
| 153 | d->w[i] = 0; |
| 154 | sym0 = *syms++; |
| 155 | sym1 = *syms++; |
| 156 | sym2 = *syms++; |
| 157 | |
| 158 | for(i=0;i<128;i++) |
| 159 | BFLY(i); |
| 160 | |
| 161 | d++; |
| 162 | tmp = vp->old_metrics; |
| 163 | vp->old_metrics = vp->new_metrics; |
| 164 | vp->new_metrics = tmp; |
| 165 | } |
| 166 | vp->dp = d; |
| 167 | return 0; |
| 168 | } |