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common/random.cpp

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+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * 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 3 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, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "common/random.h"
+#include "common/system.h"
+#include "common/config-manager.h"
+#include "gui/EventRecorder.h"
+
+
+namespace Common {
+
+RandomSource::RandomSource(const String &name) {
+	// Use system time as RNG seed. Normally not a good idea, if you are using
+	// a RNG for security purposes, but good enough for our purposes.
+	assert(g_system);
+
+#ifdef ENABLE_EVENTRECORDER
+	setSeed(g_eventRec.getRandomSeed(name));
+#else
+	setSeed(generateNewSeed());
+#endif
+}
+
+uint32 RandomSource::generateNewSeed() {
+	if (ConfMan.hasKey("random_seed"))
+		return ConfMan.getInt("random_seed");
+
+	TimeDate time;
+	g_system->getTimeAndDate(time);
+	uint32 newSeed = time.tm_sec + time.tm_min * 60U + time.tm_hour * 3600U;
+	newSeed += time.tm_mday * 86400U + time.tm_mon * 86400U * 31U;
+	newSeed += time.tm_year * 86400U * 366U;
+	newSeed = newSeed * 1000U + g_system->getMillis();
+
+	return newSeed;
+}
+
+void RandomSource::setSeed(uint32 seed) {
+	if (seed == 0)
+		seed++;
+	_randSeed = seed;
+}
+
+uint RandomSource::getRandomNumber(uint max) {
+	scrambleSeed();
+	if (max == UINT_MAX)
+		return (_randSeed * 0xDEADBF03);
+	return (_randSeed * 0xDEADBF03) % (max + 1);
+}
+
+uint RandomSource::getRandomBit() {
+	scrambleSeed();
+	return _randSeed & 1;
+}
+
+uint RandomSource::getRandomNumberRng(uint min, uint max) {
+	return getRandomNumber(max - min) + min;
+}
+
+int RandomSource::getRandomNumberRngSigned(int min, int max) {
+	return getRandomNumber(max - min) + min;
+}
+
+inline void RandomSource::scrambleSeed() {
+	//marsaglia's paper says that any of 81 triplets are feasible
+	//(11,21,13) was chosen, with (cba) and (>>,<<,>>)
+	_randSeed ^= _randSeed >> 13;
+	_randSeed ^= _randSeed << 21;
+	_randSeed ^= _randSeed >> 11;
+}
+
+} // End of namespace Common