﻿ random.cs
 File: system\random.cs Project: ndp\clr\src\bcl\mscorlib.csproj (mscorlib)
 ```// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== /*============================================================ ** ** Class: Random ** ** ** Purpose: A random number generator. ** ** ===========================================================*/ namespace System { using System; using System.Runtime; using System.Runtime.CompilerServices; using System.Globalization; using System.Diagnostics.Contracts; [System.Runtime.InteropServices.ComVisible(true)] [Serializable] public class Random { // // Private Constants // private const int MBIG = Int32.MaxValue; private const int MSEED = 161803398; private const int MZ = 0; // // Member Variables // private int inext; private int inextp; private int[] SeedArray = new int[56]; // // Public Constants // // // Native Declarations // // // Constructors // public Random() : this(Environment.TickCount) { } public Random(int Seed) { int ii; int mj, mk; //Initialize our Seed array. //This algorithm comes from Numerical Recipes in C (2nd Ed.) int subtraction = (Seed == Int32.MinValue) ? Int32.MaxValue : Math.Abs(Seed); mj = MSEED - subtraction; SeedArray[55]=mj; mk=1; for (int i=1; i<55; i++) { //Apparently the range [1..55] is special (Knuth) and so we're wasting the 0'th position. ii = (21*i)%55; SeedArray[ii]=mk; mk = mj - mk; if (mk<0) mk+=MBIG; mj=SeedArray[ii]; } for (int k=1; k<5; k++) { for (int i=1; i<56; i++) { SeedArray[i] -= SeedArray[1+(i+30)%55]; if (SeedArray[i]<0) SeedArray[i]+=MBIG; } } inext=0; inextp = 21; Seed = 1; } // // Package Private Methods // /*====================================Sample==================================== **Action: Return a new random number [0..1) and reSeed the Seed array. **Returns: A double [0..1) **Arguments: None **Exceptions: None ==============================================================================*/ protected virtual double Sample() { //Including this division at the end gives us significantly improved //random number distribution. return (InternalSample()*(1.0/MBIG)); } private int InternalSample() { int retVal; int locINext = inext; int locINextp = inextp; if (++locINext >=56) locINext=1; if (++locINextp>= 56) locINextp = 1; retVal = SeedArray[locINext]-SeedArray[locINextp]; if (retVal == MBIG) retVal--; if (retVal<0) retVal+=MBIG; SeedArray[locINext]=retVal; inext = locINext; inextp = locINextp; return retVal; } // // Public Instance Methods // /*=====================================Next===================================== **Returns: An int [0..Int32.MaxValue) **Arguments: None **Exceptions: None. ==============================================================================*/ public virtual int Next() { return InternalSample(); } private double GetSampleForLargeRange() { // The distribution of double value returned by Sample // is not distributed well enough for a large range. // If we use Sample for a range [Int32.MinValue..Int32.MaxValue) // We will end up getting even numbers only. int result = InternalSample(); // Note we can't use addition here. The distribution will be bad if we do that. bool negative = (InternalSample()%2 == 0) ? true : false; // decide the sign based on second sample if( negative) { result = -result; } double d = result; d += (Int32.MaxValue - 1); // get a number in range [0 .. 2 * Int32MaxValue - 1) d /= 2*(uint)Int32.MaxValue - 1 ; return d; } /*=====================================Next===================================== **Returns: An int [minvalue..maxvalue) **Arguments: minValue -- the least legal value for the Random number. ** maxValue -- One greater than the greatest legal return value. **Exceptions: None. ==============================================================================*/ public virtual int Next(int minValue, int maxValue) { if (minValue>maxValue) { throw new ArgumentOutOfRangeException("minValue",Environment.GetResourceString("Argument_MinMaxValue", "minValue", "maxValue")); } Contract.EndContractBlock(); long range = (long)maxValue-minValue; if( range <= (long)Int32.MaxValue) { return ((int)(Sample() * range) + minValue); } else { return (int)((long)(GetSampleForLargeRange() * range) + minValue); } } /*=====================================Next===================================== **Returns: An int [0..maxValue) **Arguments: maxValue -- One more than the greatest legal return value. **Exceptions: None. ==============================================================================*/ public virtual int Next(int maxValue) { if (maxValue<0) { throw new ArgumentOutOfRangeException("maxValue", Environment.GetResourceString("ArgumentOutOfRange_MustBePositive", "maxValue")); } Contract.EndContractBlock(); return (int)(Sample()*maxValue); } /*=====================================Next===================================== **Returns: A double [0..1) **Arguments: None **Exceptions: None ==============================================================================*/ public virtual double NextDouble() { return Sample(); } /*==================================NextBytes=================================== **Action: Fills the byte array with random bytes [0..0x7f]. The entire array is filled. **Returns:Void **Arugments: buffer -- the array to be filled. **Exceptions: None ==============================================================================*/ public virtual void NextBytes(byte [] buffer){ if (buffer==null) throw new ArgumentNullException("buffer"); Contract.EndContractBlock(); for (int i=0; i