Random.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / clr / src / BCL / System / Random.cs / 1305376 / Random.cs
                        
                        
                            // ==++== 
//
//   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=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
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