66 lines
1.7 KiB
C++
66 lines
1.7 KiB
C++
/*
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* Copyright (C) 2021 Robin Gareus <robin@gareus.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include <cassert>
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#include <climits>
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#include <ctime>
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#include "pbd/pcg_rand.h"
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using namespace PBD;
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PCGRand::PCGRand ()
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: _state (0)
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, _foo (0)
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{
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uint64_t initseq = (intptr_t)&_foo;
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_inc = (initseq << 1) | 1;
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rand_u32 ();
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_state += time (NULL) ^ (intptr_t)this;
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rand_u32 ();
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}
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/* uniform integer min <= rand < max */
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int
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PCGRand::rand (int max, int min /* = 0 */)
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{
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assert (min < max);
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assert (min > 0 || max < INT_MAX + min); // max - min overflow
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assert (min < 0 || max > INT_MIN + min); // max - min underflow
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const int range = max - min;
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while (true) {
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uint32_t value = rand_u32 ();
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if (value < 4294967295 - 4294967295 % range) {
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return min + value % range;
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}
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}
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}
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uint32_t
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PCGRand::rand_u32 ()
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{
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uint64_t oldstate = _state;
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_state = oldstate * 6364136223846793005ULL + _inc;
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uint32_t xorshifted = ((oldstate >> 18u) ^ oldstate) >> 27u;
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uint32_t rot = oldstate >> 59u;
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return (xorshifted >> rot) | (xorshifted << ((-rot) & 31));
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}
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