/* CHANNEL.C - Procedures and variables regarding channels. *//* Copyright (c) 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"/* GLOBAL VARIABLES.  Declared in channel.h. */channel_type channel;	/* Type of channel */double error_prob;	/* Error probability for BSC */double std_dev;		/* Noise standard deviation for AWGN */double lwidth;		/* Width of noise distributoin for AWLN *//* PARSE A COMMAND-LINE SPECIFICATION OF A CHANNEL.  Takes a pointer to an   argument list and an argument count; returns the number of arguments that    make up a channel specification at this point in the command line.  Returns   zero if the argument list does not start with a channel specification.   Returns -1 if there seems to be a channel specification here, but it's    invalid.   Sets the variables declared in channel.h to the type and parameters of   the channel. */int channel_parse( char **argv,		/* Pointer to argument list */  int argc		/* Number of arguments in list */){   char junk;  if (argc==0) return 0;  if (strcmp(argv[0],"bsc")==0  || strcmp(argv[0],"BSC")==0)  {     channel = BSC;    if (argc<2 || sscanf(argv[1],"%lf%c",&error_prob,&junk)!=1      || error_prob<=0 || error_prob>=1)    { return -1;    }    else    { return 2;    }  }  else if (strcmp(argv[0],"awgn")==0 || strcmp(argv[0],"AWGN")==0)  {     channel = AWGN;    if (argc<2 || sscanf(argv[1],"%lf%c",&std_dev,&junk)!=1      || std_dev<=0)    { return -1;    }    else    { return 2;    }  }  else if (strcmp(argv[0],"awln")==0 || strcmp(argv[0],"AWLN")==0)  {    channel = AWLN;    if (argc<2 || sscanf(argv[1],"%lf%c",&lwidth,&junk)!=1      || lwidth<=0)    { return -1;    }    else    { return 2;    }  }  else  {     return 0;  }}/* PRINT USAGE MESSAGE REGARDING CHANNEL SPECIFICATIONS. */void channel_usage(void){  fprintf(stderr,    "Channel: bsc error-probability | awgn standard-deviation | awln width\n");}