/* Viterbi decoder for arbitrary convolutional code
 * viterbi27 and viterbi37 for the r=1/2 and r=1/3 K=7 codes are faster
 * Copyright 1999 Phil Karn, KA9Q
 * May be used under the terms of the GNU Public License
 */

#include "itf_types.h"

#define MAX_BITS 1024

/** Modified by Ismael.
 * K, N and Polys are received as parametrs
 */


#include <memory.h>
#define NULL ((void *)0)

extern unsigned char Partab[];	/* Parity lookup table */


int VDInit;

inline int
parity(int x)
{
  x ^= (x >> 16);
  x ^= (x >> 8);
  return Partab[x & 0xff];
}
#define MAX_D  (1 << (MAX_K-6))

int mets[1 << MAX_RATE];
unsigned long paths[(MAX_BITS+MAX_K-1)*MAX_D];
long cmetric[1 << (MAX_K-1)],nmetric[1 << (MAX_K-1)];
int Syms[1 << MAX_K];

/* Viterbi decoder */
int
viterbi(
unsigned long *metric,	/* Final path metric (returned value) */
unsigned char *data,	/* Decoded output data */
unsigned char *symbols,	/* Raw deinterleaved input symbols */
unsigned int nbits,	/* Number of output bits */
int mettab[2][256],	/* Metric table, [sent sym][rx symbol] */
unsigned int startstate,         /* Encoder starting state */
unsigned int endstate,            /* Encoder ending state */

/** added by Ismael */
int N, int K, unsigned int *Polys)
{
  int bitcnt = -(K-1);
  long m0,m1;
  int i,j,sym;
  int D;
  int Rate = N;
  unsigned long *pp,mask;
  
  memset(paths,0,sizeof(paths));

  if (K>=6) {
      D	= (1 << (K-6));
  } else {
      D = 1;
  }

  if(!VDInit){
    for(i=0;i<(1<<K);i++){
      sym = 0;
      for(j=0;j<N;j++)
	sym = (sym << 1) + parity(i & Polys[j]);
      Syms[i] = sym;
    }
    VDInit++;
  }

  startstate &= ~((1<<(K-1)) - 1);
  endstate &= ~((1<<(K-1)) - 1);

  /* Initialize starting metrics */
  for(i=0;i< 1<<(K-1);i++)
    cmetric[i] = -999999;
  cmetric[startstate] = 0;

  pp = paths;
  for(;;){ /* For each data bit */
    /* Read input symbols and compute branch metrics */
    for(i=0;i< 1<<N;i++){
      mets[i] = 0;
      for(j=0;j<N;j++){
	mets[i] += mettab[(i >> (N-j-1)) & 1][symbols[j]];
      }
    }
    symbols += N;
    /* Run the add-compare-select operations */
    mask = 1;
    for(i=0;i< 1 << (K-1);i+=2){
      int b1,b2;

      b1 = mets[Syms[i]];
      nmetric[i] = m0 = cmetric[i/2] + b1;
      b2 = mets[Syms[i+1]];
      b1 -= b2;
      m1 = cmetric[(i/2) + (1<<(K-2))] + b2;
      if(m1 > m0){
	nmetric[i] = m1;
	*pp |= mask;
      }
      m0 -= b1;
      nmetric[i+1] = m0;
      m1 += b1;
      if(m1 > m0){
	nmetric[i+1] = m1;
	*pp |= mask << 1;
      }
      mask <<= 2;
      if(mask == 0){
	mask = 1;
	pp++;
      }
    }
    if(mask != 1){
      pp++;
    }
    if(++bitcnt == nbits){
      *metric = nmetric[endstate];
      break;
    }
    memcpy(cmetric,nmetric,sizeof(cmetric));
  }

  /* Chain back from terminal state to produce decoded data */
  if(data == NULL)
    return 0;/* Discard output */
  memset(data,0,(nbits+7)/8); /* round up in case nbits % 8 != 0 */

  for(i=nbits-1;i >= 0;i--){
    pp -= D;
    if(pp[endstate >> 5] & (1 << (endstate & 31))){
      endstate |= (1 << (K-1));
      data[i>>3] |= 0x80 >> (i&7);
    }
    endstate >>= 1;
  }
  return 0;
}