class/corlib/System/Random.cs

   1 //
   2 // System.Random.cs
   3 //
   4 // Authors:
   5 //   Bob Smith (bob@thestuff.net)
   6 //   Ben Maurer (bmaurer@users.sourceforge.net)
   7 //
   8 // (C) 2001 Bob Smith.  http://www.thestuff.net
   9 // (C) 2003 Ben Maurer
  10 //
  11
  12 //
  13 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
  14 //
  15 // Permission is hereby granted, free of charge, to any person obtaining
  16 // a copy of this software and associated documentation files (the
  17 // "Software"), to deal in the Software without restriction, including
  18 // without limitation the rights to use, copy, modify, merge, publish,
  19 // distribute, sublicense, and/or sell copies of the Software, and to
  20 // permit persons to whom the Software is furnished to do so, subject to
  21 // the following conditions:
  22 //
  23 // The above copyright notice and this permission notice shall be
  24 // included in all copies or substantial portions of the Software.
  25 //
  26 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  27 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  28 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  29 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  30 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  31 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  32 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  33 //
  34 using System.Runtime.InteropServices;
  35
  36 namespace System
  37 {
  38         [Serializable]
  39         [ComVisible (true)]
  40         public class Random
  41         {
  42                 const int MBIG = int.MaxValue;
  43                 const int MSEED = 161803398;
  44
  45                 int inext, inextp;
  46                 int [] SeedArray = new int [56];
  47
  48                 public Random ()
  49                         : this (Environment.TickCount)
  50                 {
  51                 }
  52
  53                 public Random (int Seed)
  54                 {
  55                         int ii;
  56                         int mj, mk;
  57
  58                         // Numerical Recipes in C online @ http://www.library.cornell.edu/nr/bookcpdf/c7-1.pdf
  59                         mj = MSEED - Math.Abs (Seed);
  60                         SeedArray [55] = mj;
  61                         mk = 1;
  62                         for (int i = 1; i < 55; i++) {  //  [1, 55] is special (Knuth)
  63                                 ii = (21 * i) % 55;
  64                                 SeedArray [ii] = mk;
  65                                 mk = mj - mk;
  66                                 if (mk < 0)
  67                                         mk += MBIG;
  68                                 mj = SeedArray [ii];
  69                         }
  70                         for (int k = 1; k < 5; k++) {
  71                                 for (int i = 1; i < 56; i++) {
  72                                         SeedArray [i] -= SeedArray [1 + (i + 30) % 55];
  73                                         if (SeedArray [i] < 0)
  74                                                 SeedArray [i] += MBIG;
  75                                 }
  76                         }
  77                         inext = 0;
  78                         inextp = 31;
  79                 }
  80
  81                 protected virtual double Sample ()
  82                 {
  83                         int retVal;
  84
  85                         if (++inext  >= 56) inext  = 1;
  86                         if (++inextp >= 56) inextp = 1;
  87
  88                         retVal = SeedArray [inext] - SeedArray [inextp];
  89
  90                         if (retVal < 0)
  91                                 retVal += MBIG;
  92
  93                         SeedArray [inext] = retVal;
  94
  95                         return retVal * (1.0 / MBIG);
  96                 }
  97
  98                 public virtual int Next ()
  99                 {
 100                         return (int)(Sample () * int.MaxValue);
 101                 }
 102
 103                 public virtual int Next (int maxValue)
 104                 {
 105                         if (maxValue < 0)
 106                                 throw new ArgumentOutOfRangeException(Locale.GetText (
 107                                         "Max value is less than min value."));
 108
 109                         return (int)(Sample () * maxValue);
 110                 }
 111
 112                 public virtual int Next (int minValue, int maxValue)
 113                 {
 114                         if (minValue > maxValue)
 115                                 throw new ArgumentOutOfRangeException (Locale.GetText (
 116                                         "Min value is greater than max value."));
 117
 118                         // special case: a difference of one (or less) will always return the minimum
 119                         // e.g. -1,-1 or -1,0 will always return -1
 120                         uint diff = (uint) (maxValue - minValue);
 121                         if (diff <= 1)
 122                                 return minValue;
 123
 124                         return (int)((uint)(Sample () * diff) + minValue);
 125                 }
 126
 127                 public virtual void NextBytes (byte [] buffer)
 128                 {
 129                         if (buffer == null)
 130                                 throw new ArgumentNullException ("buffer");
 131
 132                         for (int i = 0; i < buffer.Length; i++) {
 133                                 buffer [i] = (byte)(Sample () * (byte.MaxValue + 1));
 134                         }
 135                 }
 136
 137                 public virtual double NextDouble ()
 138                 {
 139                         return this.Sample ();
 140                 }
 141         }
 142 }