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[/] [openrisc/] [trunk/] [gnu-src/] [newlib-1.17.0/] [newlib/] [libc/] [stdlib/] [rand.c] - Rev 262
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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 */
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