citylimits/core/random.cpp

/* random.cpp
 *
 * Micropolis, Unix Version.  This game was released for the Unix platform
 * in or about 1990 and has been modified for inclusion in the One Laptop
 * Per Child program.  Copyright (C) 1989 - 2007 Electronic Arts Inc.  If
 * you need assistance with this program, you may contact:
 *   http://wiki.laptop.org/go/Micropolis  or email  micropolis@laptop.org.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or (at
 * your option) any later version.
 *
 * This program 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
 * General Public License for more details.  You should have received a
 * copy of the GNU General Public License along with this program.  If
 * not, see <http://www.gnu.org/licenses/>.
 *
 *             ADDITIONAL TERMS per GNU GPL Section 7
 *
 * No trademark or publicity rights are granted.  This license does NOT
 * give you any right, title or interest in the trademark SimCity or any
 * other Electronic Arts trademark.  You may not distribute any
 * modification of this program using the trademark SimCity or claim any
 * affliation or association with Electronic Arts Inc. or its employees.
 *
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 * versions of the program must be marked as such and not identified as
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 * NOT APPLY TO YOU.
 */

/**
 * @file random.cpp
 * @brief Contains functions for generating random numbers in
 * Micropolis.
 *
 * This file includes functions for generating random numbers used in
 * various aspects of the Micropolis game. It provides functions for
 * generating random numbers within specific ranges, signed and
 * unsigned random numbers, and a method to initialize the random
 * number generator with a random seed.
 *
 * @bug Code seems to assume that \c sizeof(short)==2 and \c
 * sizeof(int)==4 However, this depends on the compiler. We should
 * introduce typedefs for them, and check correctness of our
 * assumptions w.r.t. size of them (eg in
 * Micropolis::randomlySeedRandom() or in Micropolis::Micropolis()).
 *
 * @bug Code stores unsigned 16 bit numbers in \c short which is a
 * signed type.
 */

////////////////////////////////////////////////////////////////////////


#include "micropolis.h"


////////////////////////////////////////////////////////////////////////


/**
 * Draw a random number (internal function).
 * @todo Use Wolfram's fast cellular automata pseudo random number generator.
 * @return Unsigned 16 bit random number.
 */
int Micropolis::simRandom()
{
    nextRandom = nextRandom * 1103515245 + 12345;
    return (nextRandom & 0xffff00) >> 8;
}


/**
 * Draw a random number in a given range.
 * @param range Upper bound of the range (inclusive).
 * @return Random number between \c 0 and \a range (inclusive).
 */
short Micropolis::getRandom(short range)
{
    int maxMultiple, rnum;

    range++; /// @bug Increment may cause range overflow.
    maxMultiple = 0xffff / range;
    maxMultiple *= range;

    do {
        rnum = getRandom16();
    } while (rnum >= maxMultiple);

    return (rnum % range);
}


/**
 * Get random 16 bit number.
 * @return Unsigned 16 bit random number.
 */
int Micropolis::getRandom16()
{
    return simRandom() & 0x0000ffff;
}


/** Get signed 16 bit random number. */
int Micropolis::getRandom16Signed()
{
    int i = getRandom16();

    if (i > 0x7fff) {
      i = 0x7fff - i;
    }

    return i;
}


/**
 * Get a random number within a given range, with a preference to smaller
 * values.
 * @param limit Upper bound of the range (inclusive).
 * @return Random number between \c 0 and \a limit (inclusive).
 */
short Micropolis::getERandom(short limit)
{
    short z = getRandom(limit);
    short x = getRandom(limit);

    return min(z, x);
}


/** Initialize the random number generator with a 'random' seed. */
void Micropolis::randomlySeedRandom()
{
    struct timeval time;
    gettimeofday(&time, NULL);
    seedRandom(time.tv_usec ^ time.tv_sec);
}


/**
 * Set seed of the random number generator.
 * @param seed New seed.
 */
void Micropolis::seedRandom(int seed)
{
    nextRandom = seed;
}


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