| 0,0 → 1,91 |
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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 */ |