From b2a056e91ef73892532cc4ea5d694ec226f4db8f Mon Sep 17 00:00:00 2001
From: John Fultz <jfultz@wolfram.com>
Date: Mon, 14 Jan 2019 04:40:55 -0600
Subject: Resolve #75, update RNG to Mersenne-Twister.

---
 bag.cpp         |  2 +-
 datamanager.cpp | 15 +++++++++++----
 datamanager.h   |  6 +++++-
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/bag.cpp b/bag.cpp
index e4ebef9..a0bb102 100644
--- a/bag.cpp
+++ b/bag.cpp
@@ -101,7 +101,7 @@ void Bag::exch(const Move &move, Rack &rack)
 
 Letter Bag::pluck()
 {
-	return erase(DataManager::self()->randomNumber() % m_tiles.size());
+	return erase(DataManager::self()->randomInteger(0, m_tiles.size() - 1));
 }
 
 bool Bag::removeLetters(const LetterString &letters)
diff --git a/datamanager.cpp b/datamanager.cpp
index 445c314..32bc980 100644
--- a/datamanager.cpp
+++ b/datamanager.cpp
@@ -43,7 +43,9 @@ DataManager::DataManager()
 	m_self = this;
 	setAppDataDirectory(".");
 	setUserDataDirectory(".");
-    seedRandomNumbers((int)time(NULL));
+
+	seed_seq session_seed = {(unsigned) random_device{}(), (unsigned) time(nullptr)};
+	seedRandomNumbers(session_seed);
 
 	m_alphabetParameters = new EnglishAlphabetParameters;
 	m_evaluator = new CatchallEvaluator;
@@ -176,10 +178,15 @@ string DataManager::makeDataFilename(const string &subDirectory, const string &f
 
 void DataManager::seedRandomNumbers(unsigned int seed)
 {
-    srand(seed);
+	m_mersenneTwisterRng.seed(seed);
+}
+
+void DataManager::seedRandomNumbers(seed_seq& seed)
+{
+	m_mersenneTwisterRng.seed(seed);
 }
 
-int DataManager::randomNumber()
+int DataManager::randomInteger(int low, int high)
 {
-	return rand();
+	return uniform_int_distribution<>(low, high)(m_mersenneTwisterRng);
 }
diff --git a/datamanager.h b/datamanager.h
index 75bce54..ee896f6 100644
--- a/datamanager.h
+++ b/datamanager.h
@@ -20,6 +20,7 @@
 #define QUACKLE_DATAMANAGER_H
 
 #include <string>
+#include <random>
 
 #include "playerlist.h"
 
@@ -122,7 +123,8 @@ public:
 	string userDataDirectory() { return m_userDataDirectory; }
 
 	void seedRandomNumbers(unsigned int seed);
-	int randomNumber();
+	void seedRandomNumbers(seed_seq& seed);
+	int randomInteger(int low, int high);
 
 private:
 	static DataManager *m_self;
@@ -144,6 +146,8 @@ private:
 	StrategyParameters *m_strategyParameters;
 
 	PlayerList m_computerPlayers;
+
+	mt19937_64 m_mersenneTwisterRng;
 };
 
 inline DataManager *DataManager::self()
-- 
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