1 files changed, 165 insertions, 35 deletions

diff --git a/src/FastRandom.h b/src/FastRandom.h
index a21da8391..77bafc217 100644
--- a/src/FastRandom.h
+++ b/src/FastRandom.h
@@ -4,17 +4,10 @@
 // Declares the cFastRandom class representing a fast random number generator
 
 /*
-The cFastRandom aims to provide a very fast, although not very cryptographically secure, random generator.
-It is fast to instantiate, fast to query next, and partially multi-thread-safe.
-It is multi-thread-safe in the sense that it can be accessed from multiple threads without crashing, but it may
-yield duplicate numbers in that case.
-
-Internally, this works similar to cNoise's integral noise generation, with some predefined inputs: the seed is
-taken from a global counter and the random is calculated using a counter that is incremented on each use (hence
-the multi-thread duplication). Two alternatives exists for each function, one that takes a range parameter,
-and another that takes an additional "salt" parameter; this salt is used as an additional input to the random,
-in order to avoid multi-thread duplication. If two threads both use the class at the same time with different
-salts, the values they get will be different.
+The cFastRandom alias should be avoided in favor of the result of a call to GetRandomProvider().
+The MTRand generator used is faster, has a better range and provides higher quality randomness.
+Note that MTRand is relatively costly to construct and so instances should be long lived,
+prefer calls to GetRandomProvider over creating new instances.
 */
 
 
@@ -23,58 +16,195 @@ salts, the values they get will be different.
 
 #pragma once
 #include <random>
+#include <type_traits>
+#include <limits>
 
 
 
 
 
-class cFastRandom
+namespace Detail
+{
+	/** Returns a low quality seed. */
+	UInt32 GetRandomSeed();
+
+	/** Aliases true_type if Char is any variant of char ignoring signed-ness. */
+	template <class Char>
+	using IsChar = typename std::is_same<typename std::make_signed<Char>::type, signed char>::type;
+
+	template <class IntType>
+	struct cUniformImpl :
+		public std::conditional<
+			IsChar<IntType>::value,
+			typename std::conditional<  // Match signed-ness of IntType
+				std::is_signed<IntType>::value,
+				std::uniform_int_distribution<short>,
+				std::uniform_int_distribution<unsigned short>
+			>::type,
+			std::uniform_int_distribution<IntType>
+		>
+	{
+	};
+
+	/** uniform_int_distribution<char> is undefined so this aliases a valid type. */
+	template <class IntType>
+	using cUniform = typename cUniformImpl<IntType>::type;
+}
+
+
+
+
+
+/** Class to wrap any random engine to provide a more convenient interface. */
+template <class RandomEngine>
+class cRandomWrapper
 {
 public:
+	/** Initialize with a low quality seed. */
+	cRandomWrapper():
+		m_Engine(Detail::GetRandomSeed())
+	{
+	}
 
-	cFastRandom(void);
 
-	/** Returns a random int in the range [0 .. a_Range - 1]; a_Range must be less than 1M */
-	int NextInt(int a_Range);
+	/** Initialize with a SeedSequence. */
+	template <class SeedSeq>
+	cRandomWrapper(SeedSeq & a_SeedSeq):
+		m_Engine(a_SeedSeq)
+	{
+	}
 
-	/** Returns a random float in the range [0 .. a_Range]; a_Range must be less than 1M */
-	float NextFloat(float a_Range);
 
-	/** Returns a random float between 0 and 1. */
-	float NextFloat(void) { return NextFloat(1); }
 
-	/** Returns a random int in the range [a_Begin .. a_End] */
-	int GenerateRandomInteger(int a_Begin, int a_End);
+	/** Return a random IntType in the range [a_Min, a_Max]. */
+	template <class IntType = int, class ArgType>
+	IntType RandInt(ArgType a_Min, ArgType a_Max)
+	{
+		ASSERT(
+			(a_Max >= a_Min) &&
+			(a_Max <= std::numeric_limits<IntType>::max()) &&
+			(a_Min >= std::numeric_limits<IntType>::min())
+		);
+		Detail::cUniform<IntType> dist(
+			static_cast<IntType>(a_Min),
+			static_cast<IntType>(a_Max)
+		);
+		return static_cast<IntType>(dist(m_Engine));
+	}
 
-private:
 
-	std::minstd_rand m_LinearRand;
-};
 
 
 
+	/** Return a random IntType in the range [0, a_Max]. */
+	template <class IntType = int, class ArgType>
+	IntType RandInt(ArgType a_Max)
+	{
+		ASSERT((a_Max >= 0) && (a_Max <= std::numeric_limits<IntType>::max()));
+		Detail::cUniform<IntType> dist(IntType(0), static_cast<IntType>(a_Max));
+		return static_cast<IntType>(dist(m_Engine));
+	}
+
+
+
+
+
+	/** Return a random IntType in the range [0, std::numeric_limits<IntType>::max()]. */
+	template <class IntType = int>
+	IntType RandInt()
+	{
+		Detail::cUniform<IntType> dist(IntType(0), std::numeric_limits<IntType>::max());
+		return static_cast<IntType>(dist(m_Engine));
+	}
+
+
+
+
+
+	/** Return a random RealType in the range [a_Min, a_Max). */
+	template <class RealType = float, class ArgType>
+	RealType RandReal(ArgType a_Min, ArgType a_Max)
+	{
+		std::uniform_real_distribution<RealType> dist(a_Min, a_Max);
+		return dist(m_Engine);
+	}
 
 
-class MTRand
-{
-public:
 
-	MTRand(void);
 
-	/** Returns a random integer in the range [0 .. a_Range]. */
-	int randInt(int a_Range);
 
-	/** Returns a random integer in the range [0 .. MAX_INT]. */
-	int randInt(void);
+	/** Return a random RealType in the range [0, a_Max). */
+	template <class RealType = float, class ArgType>
+	RealType RandReal(ArgType a_Max)
+	{
+		std::uniform_real_distribution<RealType> dist(RealType(0), a_Max);
+		return dist(m_Engine);
+	}
 
-	/** Returns a random floating point number in the range [0 .. a_Range]. */
-	double rand(double a_Range);
+
+
+
+
+	/** Return a random RealType in the range [0, 1). */
+	template <class RealType = float>
+	RealType RandReal()
+	{
+		std::uniform_real_distribution<RealType> dist;
+		return dist(m_Engine);
+	}
+
+
+
+
+
+	/** Return a random bool with the given probability of being true. */
+	bool RandBool(double a_TrueProbability = 0.5)
+	{
+		std::bernoulli_distribution dist(a_TrueProbability);
+		return dist(m_Engine);
+	}
+
+
+
+
+	/** Returns a reference to the underlying random engine. */
+	RandomEngine & Engine()
+	{
+		return m_Engine;
+	}
 
 private:
 
-	std::mt19937 m_MersenneRand;
+	RandomEngine m_Engine;
 };
 
 
 
 
+
+/** Utility to seed a random engine with maximal entropy from random_device. */
+struct cRandomDeviceSeeder
+{
+	using result_type = std::random_device::result_type;
+
+	template <class Itr>
+	void generate(Itr first, Itr last)
+	{
+		std::random_device rd;
+		std::uniform_int_distribution<result_type> dist;
+		for (; first != last; ++first)
+		{
+			*first = dist(rd);
+		}
+	}
+};
+
+
+
+
+
+using cFastRandom = cRandomWrapper<std::minstd_rand>;
+using MTRand = cRandomWrapper<std::mt19937>;
+
+/** Returns the current thread's random number source. */
+MTRand & GetRandomProvider();