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livetrax/libs/pbd/pcg_rand.cc

66 lines
1.7 KiB
C++

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