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Diffstat (limited to 'src/mscorlib/src/System/Random.cs')
| -rw-r--r-- | src/mscorlib/src/System/Random.cs | 214 |
1 files changed, 214 insertions, 0 deletions
diff --git a/src/mscorlib/src/System/Random.cs b/src/mscorlib/src/System/Random.cs new file mode 100644 index 0000000000..adede6a101 --- /dev/null +++ b/src/mscorlib/src/System/Random.cs @@ -0,0 +1,214 @@ +// Licensed to the .NET Foundation under one or more agreements. +// The .NET Foundation licenses this file to you under the MIT license. +// See the LICENSE file in the project root for more information. + +/*============================================================ +** +** +** +** 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. + 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<buffer.Length; i++) { + buffer[i]=(byte)(InternalSample()%(Byte.MaxValue+1)); + } + } + } + + + +} |