Random.cs source code in C# .NET

                        Code:
                         / Dotnetfx_Vista_SP2 / Dotnetfx_Vista_SP2 / 8.0.50727.4016 / DEVDIV / depot / DevDiv / releases / whidbey / NetFxQFE / ndp / clr / src / BCL / System / Random.cs / 1 / Random.cs
                        
                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
/*============================================================
** 
** Class:  Random 
**
** 
** Purpose: A random number generator.
**
**
===========================================================*/ 
namespace System {
 
    using System; 
    using System.Runtime.CompilerServices;
    using System.Globalization; 
[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, 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.)
        mj = MSEED - Math.Abs(Seed);
        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<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",String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Argument_MinMaxValue"), "minValue", "maxValue"));
          }
 
          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", String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("ArgumentOutOfRange_MustBePositive"), "maxValue")); 
          }
          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"); 
        for (int i=0; i=56) locINext=1; 
          if (++locINextp>= 56) locINextp = 1;

          retVal = SeedArray[locINext]-SeedArray[locINextp];
 
          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",String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Argument_MinMaxValue"), "minValue", "maxValue"));
          }
 
          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", String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("ArgumentOutOfRange_MustBePositive"), "maxValue")); 
          }
          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"); 
        for (int i=0; i
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