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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 4349 | Serge | 1 | /* |
| 2 | FUNCTION |
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| 3 | < |
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| 4 | |||
| 5 | INDEX |
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| 6 | rand |
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| 7 | INDEX |
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| 8 | srand |
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| 9 | INDEX |
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| 10 | rand_r |
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| 11 | |||
| 12 | ANSI_SYNOPSIS |
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| 13 | #include |
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| 14 | int rand(void); |
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| 15 | void srand(unsigned int <[seed]>); |
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| 16 | int rand_r(unsigned int *<[seed]>); |
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| 17 | |||
| 18 | TRAD_SYNOPSIS |
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| 19 | #include |
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| 20 | int rand(); |
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| 21 | |||
| 22 | void srand(<[seed]>) |
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| 23 | unsigned int <[seed]>; |
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| 24 | |||
| 25 | void rand_r(<[seed]>) |
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| 26 | unsigned int *<[seed]>; |
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| 27 | |||
| 28 | |||
| 29 | DESCRIPTION |
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| 30 | < |
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| 31 | integer is chosen by an algorithm designed to be unpredictable, so |
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| 32 | that you can use < |
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| 33 | The algorithm depends on a static variable called the ``random seed''; |
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| 34 | starting with a given value of the random seed always produces the |
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| 35 | same sequence of numbers in successive calls to < |
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| 36 | |||
| 37 | You can set the random seed using < |
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| 38 | storing its argument in the static variable used by < |
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| 39 | exploit this to make the pseudo-random sequence less predictable, if |
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| 40 | you wish, by using some other unpredictable value (often the least |
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| 41 | significant parts of a time-varying value) as the random seed before |
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| 42 | beginning a sequence of calls to < |
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| 43 | (for example, while debugging) that successive runs of your program |
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| 44 | use the same ``random'' numbers, you can use < |
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| 45 | random seed at the outset. |
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| 46 | |||
| 47 | RETURNS |
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| 48 | < |
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| 49 | number between <<0>> and < |
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| 50 | |||
| 51 | < |
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| 52 | |||
| 53 | NOTES |
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| 54 | < |
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| 55 | < |
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| 56 | |||
| 57 | |||
| 58 | PORTABILITY |
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| 59 | < |
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| 60 | number generation is not specified; therefore, even if you use |
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| 61 | the same random seed, you cannot expect the same sequence of results |
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| 62 | on two different systems. |
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| 63 | |||
| 64 | < |
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| 65 | */ |
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| 66 | |||
| 67 | #ifndef _REENT_ONLY |
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| 68 | |||
| 69 | #include |
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| 70 | #include |
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| 71 | |||
| 72 | void |
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| 73 | _DEFUN (srand, (seed), unsigned int seed) |
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| 74 | { |
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| 4921 | Serge | 75 | struct _reent *reent = _REENT; |
| 76 | |||
| 77 | _REENT_CHECK_RAND48(reent); |
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| 78 | _REENT_RAND_NEXT(reent) = seed; |
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| 4349 | Serge | 79 | } |
| 80 | |||
| 81 | int |
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| 82 | _DEFUN_VOID (rand) |
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| 83 | { |
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| 4921 | Serge | 84 | struct _reent *reent = _REENT; |
| 85 | |||
| 4349 | Serge | 86 | /* This multiplier was obtained from Knuth, D.E., "The Art of |
| 87 | Computer Programming," Vol 2, Seminumerical Algorithms, Third |
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| 88 | Edition, Addison-Wesley, 1998, p. 106 (line 26) & p. 108 */ |
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| 4921 | Serge | 89 | _REENT_CHECK_RAND48(reent); |
| 90 | _REENT_RAND_NEXT(reent) = |
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| 91 | _REENT_RAND_NEXT(reent) * __extension__ 6364136223846793005LL + 1; |
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| 92 | return (int)((_REENT_RAND_NEXT(reent) >> 32) & RAND_MAX); |
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| 4349 | Serge | 93 | } |
| 94 | |||
| 95 | #endif /* _REENT_ONLY */ |