64 lines
1.7 KiB
C
64 lines
1.7 KiB
C
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/*
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* File: private/randompatch.h
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* ---------------------------
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* This file patches the implementation of the random number library
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* to avoid some serious bugs in standard implementations of rand,
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* particularly on Mac OS X. It also includes a hack to set the
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* seed from the RANDOM_SEED environment variable, which makes it
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* possible to produce repeatable figures.
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*/
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/*
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* Implementation notes: rand, srand
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* ---------------------------------
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* To ensure that this package works the same way on all platforms,
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* this file completely reimplements the rand and srand methods. The
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* algorithm is a conventional linear congruential generator with the
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* parameters used in GNU's gclib. RAND_MAX for this implementation
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* is 2147483647 (2^31 - 1).
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*/
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#define MULTIPLIER 1103515245
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#define OFFSET 12345
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static int _seed = 1;
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#undef rand
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#define rand() ((_seed = MULTIPLIER * _seed + OFFSET) & 0x7FFFFFFF)
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#undef srand
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#define srand(seed) (_seed = int(seed), _seed = (_seed <= 0) ? 1 : _seed)
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#undef RAND_MAX
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#define RAND_MAX 2147483647
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/*
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* Implementation notes: Windows patch
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* -----------------------------------
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* On some versions of Windows, the time function is too coarse to use
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* as a random seed. On those versions, this definition substitutes the
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* GetTickCount function.
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*/
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#if defined (_MSC_VER) && (_MSC_VER >= 1200)
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# include <windows.h>
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# define time(dummy) (GetTickCount())
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#endif
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#ifdef __APPLE__
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# include <cstdlib>
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static time_t patchedTime(time_t *) {
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char *str = getenv("RANDOM_SEED");
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if (str == NULL) {
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return time(NULL);
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} else {
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return atoi(str);
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}
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}
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# define time(dummy) patchedTime(dummy)
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#endif
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