Cosmos/source/Playgrounds/Ralf/EsxTest/MTRandom.cs

using System;
using Cosmos.Hardware;
namespace EsxTest
{
    /// <summary>
    /// http://en.wikipedia.org/wiki/Mersenne_Twister
    /// 
    /// implemented by Ralf Kronemeyer
    /// 
    /// The following generates uniformly 32-bit integers in the range [0, 2^32 − 1] with the MT19937 algorithm:
    /// 
    ///        // Create a length 624 array to store the state of the generator
    ///         int[0..623] MT
    ///         int index = 0
    ///         
    ///         // Initialize the generator from a seed
    ///         function initializeGenerator(int seed) {
    ///             MT[0] := seed
    ///             for i from 1 to 623 { // loop over each other element
    ///                 MT[i] := last 32 bits of(1812433253 * (MT[i-1] xor (right shift by 30 bits(MT[i-1]))) + i) // 0x6c078965
    ///             }
    ///         }
    ///         
    ///         // Extract a tempered pseudorandom number based on the index-th value,
    ///         // calling generateNumbers() every 624 numbers
    ///         function extractNumber() {
    ///             if index == 0 {
    ///                 generateNumbers()
    ///             }
    ///             
    ///             int y := MT[index]
    ///             y := y xor (right shift by 11 bits(y))
    ///             y := y xor (left shift by 7 bits(y) and (2636928640)) // 0x9d2c5680
    ///             y := y xor (left shift by 15 bits(y) and (4022730752)) // 0xefc60000
    ///             y := y xor (right shift by 18 bits(y))
    ///             
    ///             index := (index + 1) mod 624
    ///             return y
    ///         }
    ///         
    ///         // Generate an array of 624 untempered numbers
    ///         function generateNumbers() {
    ///             for i from 0 to 623 {
    ///                 int y := 32nd bit of(MT[i]) + last 31 bits of(MT[(i+1) mod 624])
    ///                 MT[i] := MT[(i + 397) mod 624] xor (right shift by 1 bit(y))
    ///                 if (y mod 2) == 1 { // y is odd
    ///                     MT[i] := MT[i] xor (2567483615) // 0x9908b0df
    ///                 }
    ///             }
    ///         }    
    /// 
    /// 
    /// 
    /// 
    /// 
    /// </summary>
    public static class MTRandom
    {
        private static readonly UInt32[] MT = new UInt32[624];
        private static int index;
        private static bool Initialized;

        internal static void Initialize(UInt32 seed)
        {
            MT[0] = seed;
            for (int i = 1; i < 624; i++)
            {
                MT[i] = (UInt32)(1812433253 * (MT[i - 1] ^ (MT[i - 1] >> 30)) + i);
            }
            Initialized = true;
        }

        private static void GenerateNumbers()
        {
            for (int i = 0; i < 624; i++)
            {
                UInt32 y = MT[i] + (MT[(i + 1) % 624]) & 0x7FFFFFFF;
                MT[i] = MT[(i + 397) % 624] ^ (y >> 1);
                if ((y % 2) == 1)
                {
                    MT[i] = (MT[i] ^ 0x9908b0df);
                }
            }
        }

        internal static UInt32 Next()
        {
            if (!Initialized)
            {
                Initialize((UInt32) (RTC.GetHours()*60*60 + RTC.GetMinutes()*60 + RTC.GetSeconds()));
            }
            if (index == 0)
            {
                GenerateNumbers();
            }
            UInt32 y = MT[index];
            y = y ^ (y >> 11);
            y = (y ^ ((y << 7) & 2636928640));
            y = (y ^ ((y << 15) & 0xefc60000));
            y = y ^ (y >> 18);
            index = (index + 1)%624;
            return y;
        }

        internal static UInt32 Next(UInt32 maxValue)
        {
            return Next() % maxValue;
        }
    }
}