mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-11-17 17:42:02 -05:00
345 lines
11 KiB
C
345 lines
11 KiB
C
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/*
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sfrsd.c
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A soft-decision decoder for the JT65 (63,12) Reed-Solomon code.
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This decoding scheme is built around Phil Karn's Berlekamp-Massey
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errors and erasures decoder. The approach is inspired by a number of
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publications, including the stochastic Chase decoder described
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in "Stochastic Chase Decoding of Reed-Solomon Codes", by Leroux et al.,
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IEEE Communications Letters, Vol. 14, No. 9, September 2010 and
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"Soft-Decision Decoding of Reed-Solomon Codes Using Successive Error-
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and-Erasure Decoding," by Soo-Woong Lee and B. V. K. Vijaya Kumar.
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Steve Franke K9AN, Urbana IL, September 2015
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <time.h>
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#include <string.h>
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#include "rs.h"
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static void *rs;
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//***************************************************************************
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void usage(void)
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{
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printf("Usage: sfrsd [options...] <path to kvasd.dat>\n");
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printf(" input file should be in kvasd format\n");
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printf("\n");
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printf("Options:\n");
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printf(" -n number of random erasure vectors to try\n");
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printf(" -v verbose\n");
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}
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int main(int argc, char *argv[]){
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extern char *optarg;
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extern int optind;
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int rxdat[63], rxprob[63], rxdat2[63], rxprob2[63];
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int workdat[63], correct[63];
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int era_pos[51];
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int c, i, numera, nerr, nn=63, kk=12;
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char *infile;
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FILE *datfile, *logfile;
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int nsec, maxe, nads;
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float xlambda;
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int mrsym[63],mrprob[63],mr2sym[63],mr2prob[63];
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int nsec2,ncount,dat4[12],bestdat[12];
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int ntrials=10000;
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int verbose=0;
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int nhard=0,nhard_min=32768,nsoft=0,nsoft_min=32768, ncandidates;
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while ( (c = getopt(argc, argv, "n:qv")) !=-1 ) {
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switch (c) {
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case 'n':
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ntrials=(int)strtof(optarg,NULL);
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printf("ntrials set to %d\n",ntrials);
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break;
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case 'v':
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verbose=1;
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break;
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case 'q': //accept (and ignore) -q option for WSJT10 compatibility
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break;
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case '?':
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usage();
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exit(1);
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}
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}
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if( optind+1 > argc) {
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// usage();
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// exit(1);
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infile="kvasd.dat";
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} else {
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infile=argv[optind];
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}
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logfile=fopen("/tmp/sfrsd.log","a");
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if( !logfile ) {
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printf("Unable to open sfrsd.log\n");
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exit(1);
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}
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datfile=fopen(infile,"rb");
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if( !datfile ) {
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printf("Unable to open kvasd.dat\n");
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exit(1);
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} else {
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fread(&nsec,sizeof(int),1,datfile);
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fread(&xlambda,sizeof(float),1,datfile);
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fread(&maxe,sizeof(int),1,datfile);
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fread(&nads,sizeof(int),1,datfile);
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fread(&mrsym,sizeof(int),63,datfile);
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fread(&mrprob,sizeof(int),63,datfile);
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fread(&mr2sym,sizeof(int),63,datfile);
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fread(&mr2prob,sizeof(int),63,datfile);
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fread(&nsec2,sizeof(int),1,datfile);
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fread(&ncount,sizeof(int),1,datfile);
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// printf("ncount %d\n",ncount);
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fread(&dat4,sizeof(int),12,datfile);
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fclose(datfile);
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}
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// initialize the ka9q reed solomon encoder/decoder
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unsigned int symsize=6, gfpoly=0x43, fcr=3, prim=1, nroots=51;
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rs=init_rs_int(symsize, gfpoly, fcr, prim, nroots, 0);
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/* // debug
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int revdat[12], parity[51], correct[63];
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for (i=0; i<12; i++) {
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revdat[i]=dat4[11-i];
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printf("%d ",revdat[i]);
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}
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printf("\n");
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encode_rs_int(rs,revdat,parity);
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for (i=0; i<63; i++) {
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if( i<12 ) {
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correct[i]=revdat[i];
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printf("%d ",parity[i]);
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} else {
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correct[i]=parity[i-12];
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}
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}
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printf("\n");
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*/
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// reverse the received symbol vector for bm decoder
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for (i=0; i<63; i++) {
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rxdat[i]=mrsym[62-i];
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rxprob[i]=mrprob[62-i];
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rxdat2[i]=mr2sym[62-i];
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rxprob2[i]=mr2prob[62-i];
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}
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// sort the mrsym probabilities to find the least reliable symbols
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int k, pass, tmp, nsym=63;
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int probs[63], indexes[63];
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for (i=0; i<63; i++) {
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indexes[i]=i;
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probs[i]=rxprob[i]; // must un-comment sfrsd metrics in demod64a
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}
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for (pass = 1; pass <= nsym-1; pass++) {
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for (k = 0; k < nsym - pass; k++) {
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if( probs[k] < probs[k+1] ) {
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tmp = probs[k];
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probs[k] = probs[k+1];
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probs[k+1] = tmp;
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tmp = indexes[k];
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indexes[k] = indexes[k+1];
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indexes[k+1] = tmp;
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}
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}
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}
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// see if we can decode using BM HDD (and calculate the syndrome vector)
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memset(era_pos,0,51*sizeof(int));
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numera=0;
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memcpy(workdat,rxdat,sizeof(rxdat));
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nerr=decode_rs_int(rs,workdat,era_pos,numera,1);
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if( nerr >= 0 ) {
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fprintf(logfile," BM decode nerrors= %3d : ",nerr);
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for(i=0; i<12; i++) printf("%2d ",workdat[11-i]);
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fprintf(logfile,"\n");
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fclose(logfile);
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exit(0);
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}
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// generate random erasure-locator vectors and see if any of them
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// decode. This will generate a list of potential codewords. The
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// "soft" distance between each codeword and the received word is
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// used to decide which codeword is "best".
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//
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// srandom(time(NULL));
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#ifdef WIN32
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srand(0xdeadbeef);
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#else
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srandom(0xdeadbeef);
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#endif
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float p_erase;
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int thresh, nsum;
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ncandidates=0;
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for( k=0; k<ntrials; k++) {
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memset(era_pos,0,51*sizeof(int));
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memcpy(workdat,rxdat,sizeof(rxdat));
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// mark a subset of the symbols as erasures
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numera=0;
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for (i=0; i<nn; i++) {
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p_erase=0.0;
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if( probs[62-i] >= 255 ) {
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p_erase = 0.5;
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} else if ( probs[62-i] >= 196 ) {
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p_erase = 0.6;
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} else if ( probs[62-i] >= 128 ) {
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p_erase = 0.6;
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} else if ( probs[62-i] >= 32 ) {
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p_erase = 0.6;
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} else {
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p_erase = 0.8;
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}
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thresh = p_erase*100;
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long int ir;
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#ifdef WIN32
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ir=rand();
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#else
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ir=random();
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#endif
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if( ((ir % 100) < thresh ) && numera < 51 ) {
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era_pos[numera]=indexes[62-i];
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numera=numera+1;
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}
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}
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nerr=decode_rs_int(rs,workdat,era_pos,numera,0);
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if( nerr >= 0 ) {
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ncandidates=ncandidates+1;
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for(i=0; i<12; i++) dat4[i]=workdat[11-i];
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// fprintf(logfile,"loop1 decode nerr= %3d : ",nerr);
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// for(i=0; i<12; i++) fprintf(logfile, "%2d ",dat4[i]);
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// fprintf(logfile,"\n");
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nhard=0;
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nsoft=0;
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nsum=0;
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for (i=0; i<63; i++) {
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nsum=nsum+rxprob[i];
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if( workdat[i] != rxdat[i] ) {
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nhard=nhard+1;
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nsoft=nsoft+rxprob[i];
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}
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}
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if( nsum != 0 ) {
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nsoft=63*nsoft/nsum;
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if( (nsoft < nsoft_min) ) {
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nsoft_min=nsoft;
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nhard_min=nhard;
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memcpy(bestdat,dat4,12*sizeof(int));
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memcpy(correct,workdat,63*sizeof(int));
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}
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} else {
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fprintf(logfile,"error - nsum %d nsoft %d nhard %d\n",nsum,nsoft,nhard);
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}
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// if( ncandidates >= 5000 ) {
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if( ncandidates >= ntrials/2 ) {
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break;
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}
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}
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}
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fprintf(logfile,"%d candidates after stochastic loop\n",ncandidates);
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// do Forney Generalized Minimum Distance pattern
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for (k=0; k<25; k++) {
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memset(era_pos,0,51*sizeof(int));
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numera=2*k;
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for (i=0; i<numera; i++) {
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era_pos[i]=indexes[62-i];
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}
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memcpy(workdat,rxdat,sizeof(rxdat));
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nerr=decode_rs_int(rs,workdat,era_pos,numera,0);
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if( nerr >= 0 ) {
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ncandidates=ncandidates+1;
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for(i=0; i<12; i++) dat4[i]=workdat[11-i];
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// fprintf(logfile,"GMD decode nerr= %3d : ",nerr);
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// for(i=0; i<12; i++) fprintf(logfile, "%2d ",dat4[i]);
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// fprintf(logfile,"\n");
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nhard=0;
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nsoft=0;
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nsum=0;
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for (i=0; i<63; i++) {
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nsum=nsum+rxprob[i];
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if( workdat[i] != rxdat[i] ) {
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nhard=nhard+1;
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nsoft=nsoft+rxprob[i];
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}
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}
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if( nsum != 0 ) {
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nsoft=63*nsoft/nsum;
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if( (nsoft < nsoft_min) ) {
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nsoft_min=nsoft;
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nhard_min=nhard;
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memcpy(bestdat,dat4,12*sizeof(int));
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memcpy(correct,workdat,63*sizeof(int));
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}
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} else {
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fprintf(logfile,"error - nsum %d nsoft %d nhard %d\n",nsum,nsoft,nhard);
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}
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// if( ncandidates >=5000 ) {
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if( ncandidates >= ntrials/2 ) {
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break;
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}
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}
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}
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fprintf(logfile,"%d candidates after GMD\n",ncandidates);
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if( (ncandidates >= 0) && (nsoft_min < 36) && (nhard_min < 44) ) {
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for (i=0; i<63; i++) {
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fprintf(logfile,"%3d %3d %3d %3d %3d %3d\n",i,correct[i],rxdat[i],rxprob[i],rxdat2[i],rxprob2[i]);
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// fprintf(logfile,"%3d %3d %3d %3d %3d\n",i,workdat[i],rxdat[i],rxprob[i],rxdat2[i],rxprob2[i]);
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}
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fprintf(logfile,"**** ncandidates %d nhard %d nsoft %d nsum %d\n",ncandidates,nhard_min,nsoft_min,nsum);
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} else {
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nhard_min=-1;
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memset(bestdat,0,12*sizeof(int));
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}
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datfile=fopen(infile,"wb");
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if( !datfile ) {
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printf("Unable to open kvasd.dat\n");
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return 1;
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} else {
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fwrite(&nsec,sizeof(int),1,datfile);
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fwrite(&xlambda,sizeof(float),1,datfile);
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fwrite(&maxe,sizeof(int),1,datfile);
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fwrite(&nads,sizeof(int),1,datfile);
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fwrite(&mrsym,sizeof(int),63,datfile);
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fwrite(&mrprob,sizeof(int),63,datfile);
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fwrite(&mr2sym,sizeof(int),63,datfile);
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fwrite(&mr2prob,sizeof(int),63,datfile);
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fwrite(&nsec2,sizeof(int),1,datfile);
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fwrite(&nhard_min,sizeof(int),1,datfile);
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fwrite(&bestdat,sizeof(int),12,datfile);
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fclose(datfile);
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}
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fprintf(logfile,"exiting sfrsd\n");
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fflush(logfile);
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fclose(logfile);
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exit(0);
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}
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