84 lines
1.1 KiB
C
84 lines
1.1 KiB
C
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#include <u.h>
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#include <libc.h>
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/*
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* algorithm by
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* D. P. Mitchell & J. A. Reeds
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*/
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#define LEN 607
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#define TAP 273
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#define MASK 0x7fffffffL
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#define A 48271
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#define M 2147483647
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#define Q 44488
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#define R 3399
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#define NORM (1.0/(1.0+MASK))
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static ulong rng_vec[LEN];
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static ulong* rng_tap = rng_vec;
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static ulong* rng_feed = 0;
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static Lock lk;
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static void
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isrand(long seed)
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{
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long lo, hi, x;
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int i;
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rng_tap = rng_vec;
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rng_feed = rng_vec+LEN-TAP;
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seed = seed%M;
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if(seed < 0)
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seed += M;
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if(seed == 0)
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seed = 89482311;
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x = seed;
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/*
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* Initialize by x[n+1] = 48271 * x[n] mod (2**31 - 1)
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*/
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for(i = -20; i < LEN; i++) {
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hi = x / Q;
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lo = x % Q;
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x = A*lo - R*hi;
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if(x < 0)
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x += M;
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if(i >= 0)
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rng_vec[i] = x;
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}
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}
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void
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srand(long seed)
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{
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lock(&lk);
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isrand(seed);
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unlock(&lk);
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}
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long
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lrand(void)
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{
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ulong x;
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lock(&lk);
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rng_tap--;
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if(rng_tap < rng_vec) {
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if(rng_feed == 0) {
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isrand(1);
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rng_tap--;
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}
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rng_tap += LEN;
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}
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rng_feed--;
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if(rng_feed < rng_vec)
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rng_feed += LEN;
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x = (*rng_feed + *rng_tap) & MASK;
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*rng_feed = x;
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unlock(&lk);
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return x;
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}
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