/*

==========================================================================

unifavr.c - a simple program to compute Unif[0,1] averages.
            (Designed for use in conjunction with jpar.c)

Copyright (c) 1999 by Jeffrey S. Rosenthal (jeff@math.toronto.edu).

Licensed for general copying, distribution and modification according to
the GNU General Public License (http://www.gnu.org/copyleft/gpl.html).

----------------------------------------------------

Compile with "cc unifavr.c -o unifavr".

----------------------------------------------------

USAGE:  unifavr [runningtime [seed]]

SYNOPSIS:  

unifavr will run for <runningtime> seconds (or 3 seconds if
no runningtime is given), using the drand48() pseudo-random number
generator with intial seed <seed> (or the current time in microseconds
if no seed is given).

During this time, it will continually average Unif[0,1] pseudo-random
values.

When done, it will discard any simulation in progress, and then output
two quantities: the average of the pseudo-random values considered,
and the number of such values averaged.

==========================================================================

*/

#define DEFNUMSECS 3   /* Default number of seconds to run; may be modified. */

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>

main(int argc, char *argv[])
{
    int i, N, runningsecs, tmpseed;
    float tot = 0.0;
    double tmpval;
    long presenttime();
    long starttime, runningtime;

    /* Determine running time. */
    if ( (argc >= 2) && ( (runningsecs=atoi(argv[1])) > 0 ) )
	;
    else
	runningsecs = DEFNUMSECS;
    runningtime = runningsecs * 1000000;

    /* Seed the pseudo-random number generator. */
    if ( (argc >= 3) && ( (tmpseed=atoi(argv[2])) > 0 ) )
	srand48(tmpseed);
    else
        seedrand();

    /* Prepare to begin. */
    starttime = presenttime();
    N = 0;

    /* Loop, adding up Unif[0,1] random variables. */
    while (1) {
	tmpval = drand48();
	/* Discard simulation in progress if time up. */
	if ( (N>0) && (presenttime() > starttime + runningtime) )
	    break;
	tot = tot + tmpval;
	N = N + 1;
    }
    printf("%f      %d\n", tot/N, N);

}


seedrand()
{
    struct timeval tmptv;
    int seed;

    gettimeofday (&tmptv, (struct timezone *)NULL);
    seed = (int) (tmptv.tv_usec - 1000000 * (int) 
	( ( (double) tmptv.tv_usec ) / ( (double) 1000000.0 ) ) );
    srand48(seed);
    return(0);
}


long presenttime()  /* Return present time in microseconds.  */
{
    struct timeval tmp;
    gettimeofday (&tmp, (struct timezone *)NULL);
    return (tmp.tv_usec + 1000000 * tmp.tv_sec);
}