/* TRANSMIT.C - Simulate transmission of bits through a channel. *//* Copyright (c) 2000, 2001 by Radford M. Neal  * * Permission is granted for anyone to copy, use, or modify this program  * for purposes of research or education, provided this copyright notice  * is retained, and note is made of any changes that have been made.  * * This program is distributed without any warranty, express or implied. * As this program was written for research purposes only, it has not been * tested to the degree that would be advisable in any important application. * All use of this program is entirely at the user's own risk. */#include <stdio.h>#include <stdlib.h>#include <string.h>#include <math.h>#include "channel.h"#include "open.h"#include "rand.h"void usage(void);/* MAIN PROGRAM. */int main( int argc,  char **argv){  char *tfile, *rfile;  FILE *tf, *rf;  int block_size, n_bits;  char junk;  int seed;  int cnt;  int n, b;  /* Look at arguments.  The arguments specifying the channel are looked     at by channel_parse in channel.c */  if (!(tfile = argv[1])   || !(rfile = argv[2])   || !argv[3] || sscanf(argv[3],"%d%c",&seed,&junk)!=1)  { usage();  }  n = channel_parse(argv+4,argc-4);  if (n<=0 || argc-4-n!=0)   { usage();  }  /* See if the source is all zeros or a file. */  if (sscanf(tfile,"%d%c",&n_bits,&junk)==1 && n_bits>0)  { block_size = 1;    tf = NULL;  }  else if (sscanf(tfile,"%dx%d%c",&block_size,&n_bits,&junk)==2             && block_size>0 && n_bits>0)  { n_bits *= block_size;    tf = NULL;  }  else  { tf = open_file_std(tfile,"r");    if (tf==NULL)    { fprintf(stderr,"Can't open encoded file to transmit: %s\n",tfile);      exit(1);    }  }  /* Open output file. */  rf = open_file_std(rfile,"w");  if (rf==NULL)  { fprintf(stderr,"Can't create file for received data: %s\n",rfile);    exit(1);  }  /* Set random seed to avoid duplications with other programs. */  rand_seed(10*seed+3);  /* Transmit bits. */  for (cnt = 0; ; cnt++)  {     /* Get next bit to transmit. */    if (tf) /* Data comes from a file */    {       for (;;)      { b = getc(tf);        if (b!=' ' && b!='\t' && b!='\n' && b!='\r')        { break;        }        putc(b,rf);      }      if (b==EOF) break;      if (b!='0' && b!='1')      { fprintf(stderr,"Bad character (code %d) file being transmitted\n",b);        exit(1);      }    }    else /* Data is all zeros */    {       if (cnt>0 && cnt%block_size==0)       { putc('\n',rf);      }      if (cnt==n_bits) break;      b = '0';    }    b = b=='1';    /* Produce the channel output for this transmitted bit. */        switch (channel)    { case BSC:      { int bsc_noise;        bsc_noise = rand_uniform() < error_prob;        fprintf (rf, "%d", b^bsc_noise);        break;      }      case AWGN:      { double awgn_noise;        awgn_noise = std_dev * rand_gaussian();        fprintf (rf, " %+5.2f", b ? 1+awgn_noise : -1+awgn_noise);        break;      }      case AWLN:      { double awln_noise;        awln_noise = lwidth * rand_logistic();        fprintf (rf, " %+5.2f", b ? 1+awln_noise : -1+awln_noise);        break;      }      default:      { abort();      }    }  }  fprintf(stderr,"Transmitted %d bits\n",cnt);  if (ferror(rf) || fclose(rf)!=0)  { fprintf(stderr,"Error writing received bits to %s\n",rfile);    exit(1);  }  return 0;}/* PRINT USAGE MESSAGE AND EXIT. */void usage(void){ fprintf(stderr,    "Usage:   transmit encoded-file|n-zeros received-file seed channel\n");  channel_usage();  exit(1);}