92 lines
2.7 KiB
C
92 lines
2.7 KiB
C
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/* ************************************************************************
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* File: random.c Part of CircleMUD *
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* Usage: pseudo-random number generator *
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************************************************************************ */
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/*
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* I am bothered by the non-portablility of 'rand' and 'random' -- rand
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* is ANSI C, but on some systems such as Suns, rand has seriously tragic
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* spectral properties (the low bit alternates between 0 and 1!). random
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* is better but isn't supported by all systems. So, in my quest for Ultimate
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* CircleMUD Portability, I decided to include this code for a simple but
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* relatively effective random number generator. It's not the best RNG code
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* around, but I like it because it's very short and simple, and for our
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* purposes it's "random enough".
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* --Jeremy Elson 2/23/95
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*
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* Now that we're using GNU's autoconf, I've coded Circle to always use
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* random(), and automatically link in this object file if random() isn't
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* supported on the target system. -JE 2/3/96
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*
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* Well, despite autoconf we're back to using this random all the
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* time. Oh well, there's no harm in changing my mind on this one
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* from release to release... -JE 10/28/97
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*/
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/***************************************************************************/
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/*
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*
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* This program is public domain and was written by William S. England
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* (Oct 1988). It is based on an article by:
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*
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* Stephen K. Park and Keith W. Miller. RANDOM NUMBER GENERATORS:
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* GOOD ONES ARE HARD TO FIND. Communications of the ACM,
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* New York, NY.,October 1988 p.1192
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The following is a portable c program for generating random numbers.
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The modulus and multipilier have been extensively tested and should
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not be changed except by someone who is a professional Lehmer generator
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writer. THIS GENERATOR REPRESENTS THE MINIMUM STANDARD AGAINST WHICH
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OTHER GENERATORS SHOULD BE JUDGED. ("Quote from the referenced article's
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authors. WSE" )
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*/
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#define m (unsigned long)2147483647
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#define q (unsigned long)127773
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#define a (unsigned int)16807
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#define r (unsigned int)2836
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/*
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** F(z) = (az)%m
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** = az-m(az/m)
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**
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** F(z) = G(z)+mT(z)
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** G(z) = a(z%q)- r(z/q)
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** T(z) = (z/q) - (az/m)
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**
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** F(z) = a(z%q)- rz/q+ m((z/q) - a(z/m))
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** = a(z%q)- rz/q+ m(z/q) - az
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*/
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static unsigned long seed;
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/* local functions */
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void circle_srandom(unsigned long initial_seed);
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unsigned long circle_random(void);
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void circle_srandom(unsigned long initial_seed)
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{
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seed = initial_seed;
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}
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unsigned long circle_random(void)
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{
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int lo, hi, test;
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hi = seed/q;
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lo = seed%q;
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test = a*lo - r*hi;
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if (test > 0)
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seed = test;
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else
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seed = test+ m;
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return (seed);
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}
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