Bill Yi | 4e213d5 | 2015-06-23 13:53:11 -0700 | [diff] [blame] | 1 | /* K=15 r=1/6 Viterbi decoder in portable C |
| 2 | * Copyright Mar 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 <limits.h> |
| 9 | #include "fec.h" |
| 10 | |
| 11 | typedef union { unsigned long w[512]; unsigned char c[2048];} decision_t; |
| 12 | typedef union { unsigned long w[16384]; } metric_t; |
| 13 | |
| 14 | static union branchtab615 { unsigned long w[8192]; } Branchtab615[6] __attribute__ ((aligned(16))); |
| 15 | static int Init = 0; |
| 16 | |
| 17 | /* State info for instance of Viterbi decoder */ |
| 18 | struct v615 { |
| 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 | /* Create a new instance of a Viterbi decoder */ |
| 27 | void *create_viterbi615_port(int len){ |
| 28 | struct v615 *vp; |
| 29 | |
| 30 | if(!Init){ |
| 31 | int polys[6] = { V615POLYA,V615POLYB,V615POLYC,V615POLYD,V615POLYE,V615POLYF }; |
| 32 | set_viterbi615_polynomial_port(polys); |
| 33 | } |
| 34 | if((vp = (struct v615 *)malloc(sizeof(struct v615))) == NULL) |
| 35 | return NULL; |
| 36 | if((vp->decisions = malloc((len+14)*sizeof(decision_t))) == NULL){ |
| 37 | free(vp); |
| 38 | return NULL; |
| 39 | } |
| 40 | init_viterbi615(vp,0); |
| 41 | return vp; |
| 42 | } |
| 43 | |
| 44 | void set_viterbi615_polynomial_port(int polys[6]){ |
| 45 | int state; |
| 46 | int i; |
| 47 | |
| 48 | for(state=0;state < 8192;state++){ |
| 49 | for(i=0;i<6;i++) |
| 50 | Branchtab615[i].w[state] = (polys[i] < 0) ^ parity((2*state) & abs(polys[i])) ? 255 : 0; |
| 51 | } |
| 52 | Init++; |
| 53 | } |
| 54 | |
| 55 | /* Initialize Viterbi decoder for start of new frame */ |
| 56 | int init_viterbi615_port(void *p,int starting_state){ |
| 57 | struct v615 *vp = p; |
| 58 | int i; |
| 59 | |
| 60 | if(p == NULL) |
| 61 | return -1; |
| 62 | for(i=0;i<16384;i++) |
| 63 | vp->metrics1.w[i] = 1000; |
| 64 | |
| 65 | vp->old_metrics = &vp->metrics1; |
| 66 | vp->new_metrics = &vp->metrics2; |
| 67 | vp->dp = vp->decisions; |
| 68 | vp->old_metrics->w[starting_state & 16383] = 0; /* Bias known start state */ |
| 69 | return 0; |
| 70 | } |
| 71 | |
| 72 | /* Viterbi chainback */ |
| 73 | int chainback_viterbi615_port( |
| 74 | void *p, |
| 75 | unsigned char *data, /* Decoded output data */ |
| 76 | unsigned int nbits, /* Number of data bits */ |
| 77 | unsigned int endstate){ /* Terminal encoder state */ |
| 78 | struct v615 *vp = p; |
| 79 | decision_t *d; |
| 80 | |
| 81 | if(p == NULL) |
| 82 | return -1; |
| 83 | d = (decision_t *)vp->decisions; |
| 84 | endstate %= 16384; |
| 85 | |
| 86 | /* The store into data[] only needs to be done every 8 bits. |
| 87 | * But this avoids a conditional branch, and the writes will |
| 88 | * combine in the cache anyway |
| 89 | */ |
| 90 | d += 14; /* Look past tail */ |
| 91 | while(nbits-- != 0){ |
| 92 | int k; |
| 93 | |
| 94 | k = (d[nbits].c[endstate/8] >> (endstate%8)) & 1; |
| 95 | endstate = (k << 13) | (endstate >> 1); |
| 96 | data[nbits>>3] = endstate >> 6; |
| 97 | } |
| 98 | return 0; |
| 99 | } |
| 100 | |
| 101 | /* Delete instance of a Viterbi decoder */ |
| 102 | void delete_viterbi615_port(void *p){ |
| 103 | struct v615 *vp = p; |
| 104 | |
| 105 | if(vp != NULL){ |
| 106 | free(vp->decisions); |
| 107 | free(vp); |
| 108 | } |
| 109 | } |
| 110 | |
| 111 | /* C-language butterfly */ |
| 112 | #define BFLY(i) {\ |
| 113 | unsigned long metric,m0,m1,m2,m3,decision0,decision1;\ |
| 114 | metric = ((Branchtab615[0].w[i] ^ syms[0]) + (Branchtab615[1].w[i] ^ syms[1])\ |
| 115 | +(Branchtab615[2].w[i] ^ syms[2]) + (Branchtab615[3].w[i] ^ syms[3])\ |
| 116 | +(Branchtab615[4].w[i] ^ syms[4]) + (Branchtab615[5].w[i] ^ syms[5]));\ |
| 117 | m0 = vp->old_metrics->w[i] + metric;\ |
| 118 | m1 = vp->old_metrics->w[i+8192] + (1530 - metric);\ |
| 119 | m2 = vp->old_metrics->w[i] + (1530-metric);\ |
| 120 | m3 = vp->old_metrics->w[i+8192] + metric;\ |
| 121 | decision0 = (signed long)(m0-m1) >= 0;\ |
| 122 | decision1 = (signed long)(m2-m3) >= 0;\ |
| 123 | vp->new_metrics->w[2*i] = decision0 ? m1 : m0;\ |
| 124 | vp->new_metrics->w[2*i+1] = decision1 ? m3 : m2;\ |
| 125 | d->c[i/4] |= ((decision0|(decision1<<1)) << ((2*i)&7));\ |
| 126 | } |
| 127 | /* Update decoder with a block of demodulated symbols |
| 128 | * Note that nbits is the number of decoded data bits, not the number |
| 129 | * of symbols! |
| 130 | */ |
| 131 | |
| 132 | int update_viterbi615_blk_port(void *p,unsigned char *syms,int nbits){ |
| 133 | struct v615 *vp = p; |
| 134 | void *tmp; |
| 135 | decision_t *d; |
| 136 | int i; |
| 137 | |
| 138 | if(p == NULL) |
| 139 | return -1; |
| 140 | d = (decision_t *)vp->dp; |
| 141 | while(nbits--){ |
| 142 | memset(d,0,sizeof(decision_t)); |
| 143 | for(i=0;i<8192;i++) |
| 144 | BFLY(i); |
| 145 | |
| 146 | syms += 6; |
| 147 | d++; |
| 148 | /* Swap pointers to old and new metrics */ |
| 149 | tmp = vp->old_metrics; |
| 150 | vp->old_metrics = vp->new_metrics; |
| 151 | vp->new_metrics = tmp; |
| 152 | } |
| 153 | vp->dp = d; |
| 154 | return 0; |
| 155 | } |
| 156 | |