/*
 * 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);
}
