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[/] [openrisc/] [trunk/] [gnu-src/] [newlib-1.17.0/] [newlib/] [libc/] [stdlib/] [rand_r.c] - Blame information for rev 158

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1 148 jeremybenn
#include <stdlib.h>
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/* Pseudo-random generator based on Minimal Standard by
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   Lewis, Goodman, and Miller in 1969.
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   I[j+1] = a*I[j] (mod m)
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   where a = 16807
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         m = 2147483647
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   Using Schrage's algorithm, a*I[j] (mod m) can be rewritten as:
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     a*(I[j] mod q) - r*{I[j]/q}      if >= 0
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     a*(I[j] mod q) - r*{I[j]/q} + m  otherwise
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   where: {} denotes integer division
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          q = {m/a} = 127773
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          r = m (mod a) = 2836
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   note that the seed value of 0 cannot be used in the calculation as
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   it results in 0 itself
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*/
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int
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_DEFUN (rand_r, (seed), unsigned int *seed)
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{
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        long k;
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        long s = (long)(*seed);
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        if (s == 0)
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          s = 0x12345987;
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        k = s / 127773;
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        s = 16807 * (s - k * 127773) - 2836 * k;
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        if (s < 0)
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          s += 2147483647;
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        (*seed) = (unsigned int)s;
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        return (int)(s & RAND_MAX);
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}

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