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108 lines
1.6 KiB
C
108 lines
1.6 KiB
C
/*
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* Copyright (C) 2001 Sistina Software (UK) Limited
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*
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* This file is released under the GPL.
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*/
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#include "random.h"
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#include "log.h"
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int32_t _a[56];
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int32_t *_r;
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static inline int32_t _mod_diff(int32_t x, int32_t y)
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{
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return (x - y) & 0x7fffffff;
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}
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static int32_t _flip_cycle(void)
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{
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int32_t *ii, *jj;
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for (ii = _a + 1, jj = _a + 32; jj <= _a + 55; ii++, jj++)
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*ii = _mod_diff(*ii, *jj);
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for (jj = _a + 1; ii <= _a + 55; ii++, jj++)
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*ii = _mod_diff(*ii, *jj);
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_r = _a + 54;
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return _a[55];
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}
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static void rand_init(int32_t seed)
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{
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int64_t i;
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int64_t prev = seed, next = 1;
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seed = prev = _mod_diff(prev, 0); /* strip the sign */
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_a[55] = prev;
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for (i = 21; i; i = (i + 21) % 55) {
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_a[i] = next;
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next = _mod_diff(prev, next);
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if(seed & 1)
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seed = 0x40000000L + (seed >> 1);
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else
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seed >>= 1;
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next = _mod_diff(next, seed);
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prev = _a[i];
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}
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_flip_cycle();
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_flip_cycle();
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_flip_cycle();
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_flip_cycle();
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_flip_cycle();
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}
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/*
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* FIXME: move this to be an inline in the
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* header.
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*/
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int32_t rand_get(void)
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{
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return (*_r >= 0) ? *_r-- : _flip_cycle();
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}
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/*
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* just used by rand_check
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*/
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#define t31 0x80000000
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static int32_t _uniform(int32_t m)
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{
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uint32_t t = t31 - (t31 % m);
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int32_t r;
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do
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r = next_rand(sc);
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while (t <= (uint32_t) r);
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return r % m;
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}
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/*
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* Checks I've copied the code correctly.
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*/
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int rand_check(void)
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{
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int j;
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rand_init(-314159L);
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if (next_rand(sc) != 119318998) {
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log_err("Random number generator failed check 1");
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return 0;
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}
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for(j = 1; j <= 133; j++)
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rand_get();
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if (_uniform(0x55555555L) != 748103812) {
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log_err("Random number generator failed check 2");
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return 0;
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}
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return 1;
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}
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