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/* K=15 r=1/6 Viterbi decoder in portable C
* Copyright Mar 2004, Phil Karn, KA9Q
* May be used under the terms of the GNU Lesser General Public License (LGPL)
*/
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <limits.h>
#include "fec.h"
typedef union { unsigned long w[512]; unsigned char c[2048];} decision_t;
typedef union { unsigned long w[16384]; } metric_t;
static union branchtab615 { unsigned long w[8192]; } Branchtab615[6] __attribute__ ((aligned(16)));
static int Init = 0;
/* State info for instance of Viterbi decoder */
struct v615 {
metric_t metrics1; /* path metric buffer 1 */
metric_t metrics2; /* path metric buffer 2 */
decision_t *dp; /* Pointer to current decision */
metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */
decision_t *decisions; /* Beginning of decisions for block */
};
/* Create a new instance of a Viterbi decoder */
void *create_viterbi615_port(int len){
struct v615 *vp;
if(!Init){
int polys[6] = { V615POLYA,V615POLYB,V615POLYC,V615POLYD,V615POLYE,V615POLYF };
set_viterbi615_polynomial_port(polys);
}
if((vp = (struct v615 *)malloc(sizeof(struct v615))) == NULL)
return NULL;
if((vp->decisions = malloc((len+14)*sizeof(decision_t))) == NULL){
free(vp);
return NULL;
}
init_viterbi615(vp,0);
return vp;
}
void set_viterbi615_polynomial_port(int polys[6]){
int state;
int i;
for(state=0;state < 8192;state++){
for(i=0;i<6;i++)
Branchtab615[i].w[state] = (polys[i] < 0) ^ parity((2*state) & abs(polys[i])) ? 255 : 0;
}
Init++;
}
/* Initialize Viterbi decoder for start of new frame */
int init_viterbi615_port(void *p,int starting_state){
struct v615 *vp = p;
int i;
if(p == NULL)
return -1;
for(i=0;i<16384;i++)
vp->metrics1.w[i] = 1000;
vp->old_metrics = &vp->metrics1;
vp->new_metrics = &vp->metrics2;
vp->dp = vp->decisions;
vp->old_metrics->w[starting_state & 16383] = 0; /* Bias known start state */
return 0;
}
/* Viterbi chainback */
int chainback_viterbi615_port(
void *p,
unsigned char *data, /* Decoded output data */
unsigned int nbits, /* Number of data bits */
unsigned int endstate){ /* Terminal encoder state */
struct v615 *vp = p;
decision_t *d;
if(p == NULL)
return -1;
d = (decision_t *)vp->decisions;
endstate %= 16384;
/* The store into data[] only needs to be done every 8 bits.
* But this avoids a conditional branch, and the writes will
* combine in the cache anyway
*/
d += 14; /* Look past tail */
while(nbits-- != 0){
int k;
k = (d[nbits].c[endstate/8] >> (endstate%8)) & 1;
endstate = (k << 13) | (endstate >> 1);
data[nbits>>3] = endstate >> 6;
}
return 0;
}
/* Delete instance of a Viterbi decoder */
void delete_viterbi615_port(void *p){
struct v615 *vp = p;
if(vp != NULL){
free(vp->decisions);
free(vp);
}
}
/* C-language butterfly */
#define BFLY(i) {\
unsigned long metric,m0,m1,m2,m3,decision0,decision1;\
metric = ((Branchtab615[0].w[i] ^ syms[0]) + (Branchtab615[1].w[i] ^ syms[1])\
+(Branchtab615[2].w[i] ^ syms[2]) + (Branchtab615[3].w[i] ^ syms[3])\
+(Branchtab615[4].w[i] ^ syms[4]) + (Branchtab615[5].w[i] ^ syms[5]));\
m0 = vp->old_metrics->w[i] + metric;\
m1 = vp->old_metrics->w[i+8192] + (1530 - metric);\
m2 = vp->old_metrics->w[i] + (1530-metric);\
m3 = vp->old_metrics->w[i+8192] + metric;\
decision0 = (signed long)(m0-m1) >= 0;\
decision1 = (signed long)(m2-m3) >= 0;\
vp->new_metrics->w[2*i] = decision0 ? m1 : m0;\
vp->new_metrics->w[2*i+1] = decision1 ? m3 : m2;\
d->c[i/4] |= ((decision0|(decision1<<1)) << ((2*i)&7));\
}
/* Update decoder with a block of demodulated symbols
* Note that nbits is the number of decoded data bits, not the number
* of symbols!
*/
int update_viterbi615_blk_port(void *p,unsigned char *syms,int nbits){
struct v615 *vp = p;
void *tmp;
decision_t *d;
int i;
if(p == NULL)
return -1;
d = (decision_t *)vp->dp;
while(nbits--){
memset(d,0,sizeof(decision_t));
for(i=0;i<8192;i++)
BFLY(i);
syms += 6;
d++;
/* Swap pointers to old and new metrics */
tmp = vp->old_metrics;
vp->old_metrics = vp->new_metrics;
vp->new_metrics = tmp;
}
vp->dp = d;
return 0;
}
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