/* CHANNEL.C - Procedures and variables regarding channels. */

/* Copyright (c) 2001 by Radford M. Neal 
 *
 * Permission is granted for anyone to copy, use, modify, or distribute this
 * program and accompanying programs and documents for any purpose, provided 
 * this copyright notice is retained and prominently displayed, along with
 * a note saying that the original programs are available from Radford Neal's
 * web page, and note is made of any changes made to the programs.  The
 * programs and documents are distributed without any warranty, express or
 * implied.  As the programs were written for research purposes only, they have
 * not been tested to the degree that would be advisable in any important
 * application.  All use of these programs 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 distribution 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");
}