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/*

FUNCTION

<<rand>>, <<srand>>---pseudo-random numbers

INDEX

        rand

INDEX

        srand

INDEX

        rand_r

ANSI_SYNOPSIS

        #include <stdlib.h>

        int rand(void);

        void srand(unsigned int <[seed]>);

        int rand_r(unsigned int *<[seed]>);

TRAD_SYNOPSIS

        #include <stdlib.h>

        int rand();

        void srand(<[seed]>)

        unsigned int <[seed]>;

        void rand_r(<[seed]>)

        unsigned int *<[seed]>;

DESCRIPTION

<<rand>> returns a different integer each time it is called; each

integer is chosen by an algorithm designed to be unpredictable, so

that you can use <<rand>> when you require a random number.

The algorithm depends on a static variable called the ``random seed'';

starting with a given value of the random seed always produces the

same sequence of numbers in successive calls to <<rand>>.

You can set the random seed using <<srand>>; it does nothing beyond

storing its argument in the static variable used by <<rand>>.  You can

exploit this to make the pseudo-random sequence less predictable, if

you wish, by using some other unpredictable value (often the least

significant parts of a time-varying value) as the random seed before

beginning a sequence of calls to <<rand>>; or, if you wish to ensure

(for example, while debugging) that successive runs of your program

use the same ``random'' numbers, you can use <<srand>> to set the same

random seed at the outset.

RETURNS

<<rand>> returns the next pseudo-random integer in sequence; it is a

number between <<0>> and <<RAND_MAX>> (inclusive).

<<srand>> does not return a result.

NOTES

<<rand>> and <<srand>> are unsafe for multi-threaded applications.

<<rand_r>> is thread-safe and should be used instead.

PORTABILITY

<<rand>> is required by ANSI, but the algorithm for pseudo-random

number generation is not specified; therefore, even if you use

the same random seed, you cannot expect the same sequence of results

on two different systems.

<<rand>> requires no supporting OS subroutines.

*/

#ifndef _REENT_ONLY

#include <stdlib.h>

#include <reent.h>

void

_DEFUN (srand, (seed), unsigned int seed)

{

  _REENT_CHECK_RAND48(_REENT);

  _REENT_RAND_NEXT(_REENT) = seed;

}

int

_DEFUN_VOID (rand)

{

  /* This multiplier was obtained from Knuth, D.E., "The Art of

     Computer Programming," Vol 2, Seminumerical Algorithms, Third

     Edition, Addison-Wesley, 1998, p. 106 (line 26) & p. 108 */

  _REENT_CHECK_RAND48(_REENT);

  _REENT_RAND_NEXT(_REENT) =

     _REENT_RAND_NEXT(_REENT) * __extension__ 6364136223846793005LL + 1;

  return (int)((_REENT_RAND_NEXT(_REENT) >> 32) & RAND_MAX);

}

#endif /* _REENT_ONLY */