mirror of
https://github.com/autc04/Retro68.git
synced 2024-11-28 05:51:04 +00:00
92 lines
2.5 KiB
C
92 lines
2.5 KiB
C
/*
|
|
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 */
|