54 lines
1.1 KiB
C
54 lines
1.1 KiB
C
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/* lrand(3)
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*
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* Author: Terrence W. Holm Nov. 1988
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*
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*
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* A prime modulus multiplicative linear congruential
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* generator (PMMLCG), or "Lehmer generator".
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* Implementation directly derived from the article:
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*
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* S. K. Park and K. W. Miller
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* Random Number Generators: Good Ones are Hard to Find
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* CACM vol 31, #10. Oct. 1988. pp 1192-1201.
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*
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*
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* Using the following multiplier and modulus, we obtain a
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* generator which:
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*
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* 1) Has a full period: 1 to 2^31 - 2.
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* 2) Is testably "random" (see the article).
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* 3) Has a known implementation by E. L. Schrage.
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*/
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#include <lib.h>
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_PROTOTYPE( long seed, (long lseed));
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_PROTOTYPE( long lrand, (void));
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#define A 16807L /* A "good" multiplier */
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#define M 2147483647L /* Modulus: 2^31 - 1 */
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#define Q 127773L /* M / A */
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#define R 2836L /* M % A */
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PRIVATE long _lseed = 1L;
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long seed(lseed)
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long lseed;
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{
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long previous_seed = _lseed;
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_lseed = lseed;
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return(previous_seed);
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}
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long lrand()
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{
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_lseed = A * (_lseed % Q) - R * (_lseed / Q);
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if (_lseed < 0) _lseed += M;
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return(_lseed);
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}
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