PROWAREtech

articles » current » dot-net » mersenne-twister-random-number-generator

.NET: Mersenne Twister Random Number Generation

A popular Mersenne Twister pseudo random number generator example written in C#.

The widely used Mersenne Twister is a pseudorandom number generator for the C# programmer. For a C++ implementation, see this article.


// Mersenne.cs
using System;

namespace PseudoRandom
{
	public class RandomMersenne
	{
		const int MERS_N = 624;
		const int MERS_M = 397;
		const int MERS_U = 11;
		const int MERS_S = 7;
		const int MERS_T = 15;
		const int MERS_L = 18;
		const uint MERS_A = 0x9908B0DF;
		const uint MERS_B = 0x9D2C5680;
		const uint MERS_C = 0xEFC60000;

		uint[] mt = new uint[MERS_N];		   // state vector
		uint mti;							 // index into mt

		private RandomMersenne() { }
		public RandomMersenne(uint seed)
		{		// constructor
			RandomInit(seed);
		}
		public void RandomInit(uint seed)
		{
			mt[0] = seed;
			for (mti = 1; mti < MERS_N; mti++)
				mt[mti] = (1812433253U * (mt[mti - 1] ^ (mt[mti - 1] >> 30)) + mti);
		}
		public void RandomInitByArray(uint[] seeds)
		{
			// seed by more than 32 bits
			uint i, j;
			int k;
			int length = seeds.Length;
			RandomInit(19650218U);
			if (length <= 0) return;
			i = 1; j = 0;
			k = (MERS_N > length ? MERS_N : length);
			for (; k != 0; k--)
			{
				mt[i] = (mt[i] ^ ((mt[i - 1] ^ (mt[i - 1] >> 30)) * 1664525U)) + seeds[j] + j;
				i++; j++;
				if (i >= MERS_N) { mt[0] = mt[MERS_N - 1]; i = 1; }
				if (j >= length) j = 0;
			}
			for (k = MERS_N - 1; k != 0; k--)
			{
				mt[i] = (mt[i] ^ ((mt[i - 1] ^ (mt[i - 1] >> 30)) * 1566083941U)) - i;
				if (++i >= MERS_N) { mt[0] = mt[MERS_N - 1]; i = 1; }
			}
			mt[0] = 0x80000000U; // MSB is 1; assuring non-zero initial array
		}
		public int IRandom(int min, int max)
		{
			// output random integer in the interval min <= x <= max
			int r;
			r = (int)((max - min + 1) * Random()) + min; // multiply interval with random and truncate
			if (r > max)
				r = max;
			if (max < min)
				return -2147483648;
			return r;
		}
		public double Random()
		{
			// output random float number in the interval 0 <= x < 1
			uint r = BRandom(); // get 32 random bits
			if (BitConverter.IsLittleEndian)
			{
				byte[] i0 = BitConverter.GetBytes((r << 20));
				byte[] i1 = BitConverter.GetBytes(((r >> 12) | 0x3FF00000));
				byte[] bytes = { i0[0], i0[1], i0[2], i0[3], i1[0], i1[1], i1[2], i1[3] };
				double f = BitConverter.ToDouble(bytes, 0);
				return f - 1.0;
			}
			return r * (1.0/(0xFFFFFFFF + 1.0));
		}
		public uint BRandom()
		{
			// generate 32 random bits
			uint y;

			if (mti >= MERS_N)
			{
				const uint LOWER_MASK = 2147483647;
				const uint UPPER_MASK = 0x80000000;
				uint[] mag01 = { 0, MERS_A };

				int kk;
				for (kk = 0; kk < MERS_N - MERS_M; kk++)
				{
					y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK);
					mt[kk] = mt[kk + MERS_M] ^ (y >> 1) ^ mag01[y & 1];
				}

				for (; kk < MERS_N - 1; kk++)
				{
					y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK);
					mt[kk] = mt[kk + (MERS_M - MERS_N)] ^ (y >> 1) ^ mag01[y & 1];
				}

				y = (mt[MERS_N - 1] & UPPER_MASK) | (mt[0] & LOWER_MASK);
				mt[MERS_N - 1] = mt[MERS_M - 1] ^ (y >> 1) ^ mag01[y & 1];
				mti = 0;
			}

			y = mt[mti++];

			// Tempering (May be omitted):
			y ^= y >> MERS_U;
			y ^= (y << MERS_S) & MERS_B;
			y ^= (y << MERS_T) & MERS_C;
			y ^= y >> MERS_L;
			return y;
		}
	}
}

Generate the seed using Guid.NewGuid().GetHashCode().


using System;
using PseudoRandom;

namespace ConsoleApp1
{
	class Program
	{
		static void Main(string[] args)
		{
			int seed = Guid.NewGuid().GetHashCode(); // this should always generate a good number for the seed
			RandomMersenne m = new RandomMersenne((uint)seed);
			for(int i = 0; i < 25; i++)
				Console.Write(m.IRandom(0, 100) + " ");
		}
	}
}

Coding Video

https://youtu.be/RwZYHR5Cut4


This site uses cookies. Cookies are simple text files stored on the user's computer. They are used for adding features and security to this site. Read the privacy policy.
CLOSE