cuberite-2a/src/FastRandom.h

// FastRandom.h

// 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.
*/





#pragma once
#include <random>





class cFastRandom
{
public:

	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);

	/** Returns a random int in the range [0 .. a_Range - 1]; a_Range must be less than 1M; a_Salt is additional source of randomness */
	int NextInt(int a_Range, int a_Salt);
	
	/** 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 in the range [0 .. a_Range]; a_Range must be less than 1M; a_Salt is additional source of randomness */
	float NextFloat(float a_Range, int a_Salt);

	/** 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);

private:

	std::minstd_rand m_LinearRand;
};





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);

	/** Returns a random floating point number in the range [0 .. a_Range]. */
	double rand(double a_Range);

private:

	std::mt19937 m_MersenneRand;
};