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https://github.com/libretro/scummvm.git
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eff98b0c56
The 'time.tm_year * 86400 * 366' line caused the result to overflow what can be stored in an int; and signed int overflow is undefined behaviour. The result goes into an unsigned int anyway, so now all the intermediate computations are also done with unsigned int. It still overflows (not on this line, but on the next one), but that is fine as the standard guarantees that unsigned int overflow wraps around.
82 lines
2.4 KiB
C++
82 lines
2.4 KiB
C++
/* ScummVM - Graphic Adventure Engine
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*
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* ScummVM is the legal property of its developers, whose names
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* are too numerous to list here. Please refer to the COPYRIGHT
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* file distributed with this source distribution.
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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 3 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
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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#include "common/random.h"
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#include "common/system.h"
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#include "gui/EventRecorder.h"
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namespace Common {
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RandomSource::RandomSource(const String &name) {
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// Use system time as RNG seed. Normally not a good idea, if you are using
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// a RNG for security purposes, but good enough for our purposes.
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assert(g_system);
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#ifdef ENABLE_EVENTRECORDER
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setSeed(g_eventRec.getRandomSeed(name));
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#else
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TimeDate time;
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g_system->getTimeAndDate(time);
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uint32 newSeed = time.tm_sec + time.tm_min * 60U + time.tm_hour * 3600U;
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newSeed += time.tm_mday * 86400U + time.tm_mon * 86400U * 31U;
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newSeed += time.tm_year * 86400U * 366U;
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newSeed = newSeed * 1000U + g_system->getMillis();
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setSeed(newSeed);
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#endif
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}
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void RandomSource::setSeed(uint32 seed) {
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if (seed == 0)
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seed++;
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_randSeed = seed;
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}
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uint RandomSource::getRandomNumber(uint max) {
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scrambleSeed();
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if (max == UINT_MAX)
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return (_randSeed * 0xDEADBF03);
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return (_randSeed * 0xDEADBF03) % (max + 1);
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}
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uint RandomSource::getRandomBit() {
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scrambleSeed();
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return _randSeed & 1;
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}
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uint RandomSource::getRandomNumberRng(uint min, uint max) {
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return getRandomNumber(max - min) + min;
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}
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int RandomSource::getRandomNumberRngSigned(int min, int max) {
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return getRandomNumber(max - min) + min;
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}
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inline void RandomSource::scrambleSeed() {
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//marsaglia's paper says that any of 81 triplets are feasible
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//(11,21,13) was chosen, with (cba) and (>>,<<,>>)
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_randSeed ^= _randSeed >> 13;
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_randSeed ^= _randSeed << 21;
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_randSeed ^= _randSeed >> 11;
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}
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} // End of namespace Common
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