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- // ==++==
- //
- // 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
- ==============================================================================*/
- #if !FEATURE_CORECLR
- [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
- #endif
- 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.
- ==============================================================================*/
- #if !FEATURE_CORECLR
- [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
- #endif
- 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
- ==============================================================================*/
- #if !FEATURE_CORECLR
- [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
- #endif
- 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));
- }
- }
- }
- }
- // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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