/*
 * randbitrun - check rand bit run lengths of the subtractive 100 shuffle generator
 *
 * Copyright (C) 1999,2023  Landon Curt Noll
 *
 * Calc is open software; you can redistribute it and/or modify it under
 * the terms of the version 2.1 of the GNU Lesser General Public License
 * as published by the Free Software Foundation.
 *
 * Calc is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
 * Public License for more details.
 *
 * A copy of version 2.1 of the GNU Lesser General Public License is
 * distributed with calc under the filename COPYING-LGPL.  You should have
 * received a copy with calc; if not, write to Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 * Under source code control:	1995/02/13 03:43:11
 * File existed as early as:	1995
 *
 * chongo <was here> /\oo/\	http://www.isthe.com/chongo/
 * Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
 */

/*
 * We will use randbit(1) to generate a stream if single bits.
 * The odds that we will have n bits the same in a row is 1/2^n.
 */


define randbitrun(run_cnt)
{
    local i;			/* index */
    local max_run;		/* longest run */
    local long_run_cnt;		/* number of runs longer than MAX_RUN */
    local run;			/* current run length */
    local tally_sum;		/* sum of all tally values */
    local last;			/* last random number */
    local current;		/* current random number */
    local MAX_RUN = 18;		/* max run we will keep track of */
    local mat tally[1:MAX_RUN]; /* tally of length of a rise run of 'x' */
    local mat prob[1:MAX_RUN];	/* prob[x] = probability of 'x' length run */

    /*
     * parse args
     */
    if (param(0) == 0) {
	run_cnt = 65536;
    }

    /*
     * run setup
     */
    max_run = 0;		/* no runs yet */
    long_run_cnt = 0;		/* no long runs set */
    current = randbit(1);	/* our first number */
    run = 1;

    /*
     * compute the run length probabilities
     *
     * A bit run length of 'r' occurs with a probability of:
     *
     *			1/2^n;
     */
    for (i=1; i <= MAX_RUN; ++i) {
	prob[i] = 1.0/(1<<i);
    }

    /*
     * look at a number of random number trials
     */
    for (i=0; i < run_cnt; ++i) {

	/* get our current number */
	last = current;
	current = randbit(1);

	/* look for a run break */
	if (current != last) {

	    /*	record the stats */
	    if (run > max_run) {
		max_run = run;
	    }
	    if (run > MAX_RUN) {
		++long_run_cnt;
	    } else {
		++tally[run];
	    }

	    /* start a new run */
	    current = randbit(1);
	    run = 1;

	/* note the continuing run */
	} else {
	    ++run;
	}
    }
    /* determine the number of runs found */
    tally_sum = matsum(tally) + long_run_cnt;

    /*
     * print the stats
     */
    printf("rand runbit test used %d values to produce %d runs\n",
      run_cnt, tally_sum);
    for (i=1; i <= MAX_RUN; ++i) {
	printf("length=%d\tprob=%9.7f\texpect=%d \tcount=%d \terr=%9.7f\n",
	  i, prob[i], round(tally_sum*prob[i]), tally[i],
	  (tally[i] - round(tally_sum*prob[i]))/tally_sum);
    }
    printf("length>%d\t\t\t\t\tcount=%d\n", MAX_RUN, long_run_cnt);
    printf("max length=%d\n", max_run);
}
