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/* K=9 r=1/2 Viterbi decoder in portable C
* Copyright Feb 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 "fec.h"
typedef union { unsigned int w[256]; } metric_t;
typedef union { unsigned long w[8];} decision_t;
static union { unsigned char c[128]; } Branchtab29[2];
static int Init = 0;
/* State info for instance of Viterbi decoder */
struct v29 {
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 */
};
/* Initialize Viterbi decoder for start of new frame */
int init_viterbi29_port(void *p,int starting_state){
struct v29 *vp = p;
int i;
if(p == NULL)
return -1;
for(i=0;i<256;i++)
vp->metrics1.w[i] = 63;
vp->old_metrics = &vp->metrics1;
vp->new_metrics = &vp->metrics2;
vp->dp = vp->decisions;
vp->old_metrics->w[starting_state & 255] = 0; /* Bias known start state */
return 0;
}
void set_viterbi29_polynomial_port(int polys[2]){
int state;
for(state=0;state < 128;state++){
Branchtab29[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
Branchtab29[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
}
Init++;
}
/* Create a new instance of a Viterbi decoder */
void *create_viterbi29_port(int len){
struct v29 *vp;
if(!Init){
int polys[2] = {V29POLYA,V29POLYB};
set_viterbi29_polynomial_port(polys);
}
if((vp = (struct v29 *)malloc(sizeof(struct v29))) == NULL)
return NULL;
if((vp->decisions = (decision_t *)malloc((len+8)*sizeof(decision_t))) == NULL){
free(vp);
return NULL;
}
init_viterbi29_port(vp,0);
return vp;
}
/* Viterbi chainback */
int chainback_viterbi29_port(
void *p,
unsigned char *data, /* Decoded output data */
unsigned int nbits, /* Number of data bits */
unsigned int endstate){ /* Terminal encoder state */
struct v29 *vp = p;
decision_t *d;
if(p == NULL)
return -1;
d = vp->decisions;
/* Make room beyond the end of the encoder register so we can
* accumulate a full byte of decoded data
*/
endstate %= 256;
/* 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 += 8; /* Look past tail */
while(nbits-- != 0){
int k;
k = (d[nbits].w[(endstate)/32] >> (endstate%32)) & 1;
data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
}
return 0;
}
/* Delete instance of a Viterbi decoder */
void delete_viterbi29_port(void *p){
struct v29 *vp = p;
if(vp != NULL){
free(vp->decisions);
free(vp);
}
}
/* C-language butterfly */
#define BFLY(i) {\
unsigned int metric,m0,m1,decision;\
metric = (Branchtab29[0].c[i] ^ sym0) + (Branchtab29[1].c[i] ^ sym1);\
m0 = vp->old_metrics->w[i] + metric;\
m1 = vp->old_metrics->w[i+128] + (510 - metric);\
decision = (signed int)(m0-m1) > 0;\
vp->new_metrics->w[2*i] = decision ? m1 : m0;\
d->w[i/16] |= decision << ((2*i)&31);\
m0 -= (metric+metric-510);\
m1 += (metric+metric-510);\
decision = (signed int)(m0-m1) > 0;\
vp->new_metrics->w[2*i+1] = decision ? m1 : m0;\
d->w[i/16] |= decision << ((2*i+1)&31);\
}
/* 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_viterbi29_blk_port(void *p,unsigned char *syms,int nbits){
struct v29 *vp = p;
decision_t *d;
if(p == NULL)
return -1;
d = (decision_t *)vp->dp;
while(nbits--){
void *tmp;
unsigned char sym0,sym1;
int i;
for(i=0;i<8;i++)
d->w[i] = 0;
sym0 = *syms++;
sym1 = *syms++;
for(i=0;i<128;i++)
BFLY(i);
d++;
tmp = vp->old_metrics;
vp->old_metrics = vp->new_metrics;
vp->new_metrics = tmp;
}
vp->dp = d;
return 0;
}
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