From 360d8eade0332f2c1aa5c205ca772cd506c35b26 Mon Sep 17 00:00:00 2001
From: peterbell10 <peterbell10@live.co.uk>
Date: Tue, 13 Jun 2017 20:35:30 +0100
Subject: FastRandom rewrite (#3754)

---
 src/FastRandom.cpp | 119 ++++++++++++++---------------------------------------
 1 file changed, 30 insertions(+), 89 deletions(-)

(limited to 'src/FastRandom.cpp')

diff --git a/src/FastRandom.cpp b/src/FastRandom.cpp
index 718092aee..de33a112c 100644
--- a/src/FastRandom.cpp
+++ b/src/FastRandom.cpp
@@ -1,11 +1,11 @@
 
 // FastRandom.cpp
 
-// Implements the cFastRandom class representing a fast random number generator
 
 #include "Globals.h"
 #include "FastRandom.h"
 
+#include <mutex>
 #include <random>
 
 #if defined (__GNUC__)
@@ -13,109 +13,50 @@
 #elif defined (_MSC_VER)
 	#define ATTRIBUTE_TLS static __declspec(thread)
 #else
-	#error "Unknown thread local storage qualifier"
+	#define ATTRIBUTE_TLS thread_local
 #endif
 
-static unsigned int GetRandomSeed()
-{
-	ATTRIBUTE_TLS bool SeedCounterInitialized = 0;
-	ATTRIBUTE_TLS unsigned int SeedCounter = 0;
-
-	if (!SeedCounterInitialized)
-	{
-		std::random_device rd;
-		std::uniform_int_distribution<unsigned int> dist;
-		SeedCounter = dist(rd);
-		SeedCounterInitialized = true;
-	}
-	return ++SeedCounter;
-}
-
-
-
-
-////////////////////////////////////////////////////////////////////////////////
-// cFastRandom:
-
-
-
-
-
-cFastRandom::cFastRandom(void) :
-	m_LinearRand(GetRandomSeed())
-{
-}
-
-
-
-
-
-int cFastRandom::NextInt(int a_Range)
-{
-	std::uniform_int_distribution<> distribution(0, a_Range - 1);
-	return distribution(m_LinearRand);
-}
-
-
-
-
-
-
-float cFastRandom::NextFloat(float a_Range)
-{
-	std::uniform_real_distribution<float> distribution(0, a_Range);
-	return distribution(m_LinearRand);
-}
-
-
 
 
 
 
-int cFastRandom::GenerateRandomInteger(int a_Begin, int a_End)
+MTRand & GetRandomProvider()
 {
-	std::uniform_int_distribution<> distribution(a_Begin, a_End);
-	return distribution(m_LinearRand);
-}
-
-
-
-
-
-////////////////////////////////////////////////////////////////////////////////
-// MTRand:
-
-MTRand::MTRand() :
-	m_MersenneRand(GetRandomSeed())
-{
-}
-
-
-
+	// Some compilers don't support thread_local for non-POD types, this is purely a work around for that restriction.
+	// There should be minimal overhead for the non-initializing case and all thread's instances are deleted properly.
+	ATTRIBUTE_TLS MTRand * LocalPtr = nullptr;
+	if (LocalPtr == nullptr)
+	{
+		// This list allows deletion of elements as if they had static storage duration
+		static std::mutex CSDeleteList;
+		static std::list<std::unique_ptr<MTRand>> DeleteList;
 
+		cRandomDeviceSeeder seeder;
+		auto NewInstance = cpp14::make_unique<MTRand>(seeder);
+		auto TempPtr = NewInstance.get();
 
-int MTRand::randInt(int a_Range)
-{
-	std::uniform_int_distribution<> distribution(0, a_Range);
-	return distribution(m_MersenneRand);
+		std::lock_guard<std::mutex> Lock(CSDeleteList);
+		DeleteList.push_front(std::move(NewInstance));
+		LocalPtr = TempPtr;  // Set after push_back so LocalPtr won't dangle if it throws
+	}
+	return *LocalPtr;
 }
 
 
 
 
 
-int MTRand::randInt()
+UInt32 Detail::GetRandomSeed()
 {
-	std::uniform_int_distribution<> distribution(0, std::numeric_limits<int>::max());
-	return distribution(m_MersenneRand);
-}
-
-
-
-
+	ATTRIBUTE_TLS bool SeedCounterInitialized = false;
+	ATTRIBUTE_TLS UInt32 SeedCounter = 0;
 
-double MTRand::rand(double a_Range)
-{
-	std::uniform_real_distribution<> distribution(0, a_Range);
-	return distribution(m_MersenneRand);
+	if (!SeedCounterInitialized)
+	{
+		std::random_device rd;
+		std::uniform_int_distribution<UInt32> dist;
+		SeedCounter = dist(rd);
+		SeedCounterInitialized = true;
+	}
+	return ++SeedCounter;
 }
-- 
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