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/* K=7 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 <limits.h>
#include "fec.h"
typedef union { unsigned int w[64]; } metric_t;
typedef union { unsigned long w[2];} decision_t;
static union branchtab27 { unsigned char c[32]; } Branchtab27[2] __attribute__ ((aligned(16)));
static int Init = 0;
/* State info for instance of Viterbi decoder
* Don't change this without also changing references in [mmx|sse|sse2]bfly29.s!
*/
struct v27 {
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_viterbi27_port(void *p,int starting_state){
struct v27 *vp = p;
int i;
if(p == NULL)
return -1;
for(i=0;i<64;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 & 63] = 0; /* Bias known start state */
return 0;
}
void set_viterbi27_polynomial_port(int polys[2]){
int state;
for(state=0;state < 32;state++){
Branchtab27[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
Branchtab27[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_viterbi27_port(int len){
struct v27 *vp;
if(!Init){
int polys[2] = { V27POLYA, V27POLYB };
set_viterbi27_polynomial_port(polys);
}
if((vp = malloc(sizeof(struct v27))) == NULL)
return NULL;
if((vp->decisions = malloc((len+6)*sizeof(decision_t))) == NULL){
free(vp);
return NULL;
}
init_viterbi27_port(vp,0);
return vp;
}
/* Viterbi chainback */
int chainback_viterbi27_port(
void *p,
unsigned char *data, /* Decoded output data */
unsigned int nbits, /* Number of data bits */
unsigned int endstate){ /* Terminal encoder state */
struct v27 *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 %= 64;
endstate <<= 2;
/* 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 += 6; /* Look past tail */
while(nbits-- != 0){
int k;
k = (d[nbits].w[(endstate>>2)/32] >> ((endstate>>2)%32)) & 1;
data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
}
return 0;
}
/* Delete instance of a Viterbi decoder */
void delete_viterbi27_port(void *p){
struct v27 *vp = p;
if(vp != NULL){
free(vp->decisions);
free(vp);
}
}
/* C-language butterfly */
#define BFLY(i) {\
unsigned int metric,m0,m1,decision;\
metric = (Branchtab27[0].c[i] ^ sym0) + (Branchtab27[1].c[i] ^ sym1);\
m0 = vp->old_metrics->w[i] + metric;\
m1 = vp->old_metrics->w[i+32] + (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_viterbi27_blk_port(void *p,unsigned char *syms,int nbits){
struct v27 *vp = p;
void *tmp;
decision_t *d;
if(p == NULL)
return -1;
d = (decision_t *)vp->dp;
while(nbits--){
unsigned char sym0,sym1;
d->w[0] = d->w[1] = 0;
sym0 = *syms++;
sym1 = *syms++;
BFLY(0);
BFLY(1);
BFLY(2);
BFLY(3);
BFLY(4);
BFLY(5);
BFLY(6);
BFLY(7);
BFLY(8);
BFLY(9);
BFLY(10);
BFLY(11);
BFLY(12);
BFLY(13);
BFLY(14);
BFLY(15);
BFLY(16);
BFLY(17);
BFLY(18);
BFLY(19);
BFLY(20);
BFLY(21);
BFLY(22);
BFLY(23);
BFLY(24);
BFLY(25);
BFLY(26);
BFLY(27);
BFLY(28);
BFLY(29);
BFLY(30);
BFLY(31);
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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