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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)
{
struct _reent *reent = _REENT;
_REENT_CHECK_RAND48(reent);
_REENT_RAND_NEXT(reent) = seed;
}
int
_DEFUN_VOID (rand)
{
struct _reent *reent = _REENT;
/* 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 */
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