mcs/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
  35 namespace System
  36 {
  37         [Serializable]
  38         public class Random
  39         {
  40                 const int MBIG = int.MaxValue;
  41                 const int MSEED = 161803398;
  42                 const int MZ = 0;
  43
  44                 int inext, inextp;
  45                 int [] SeedArray = new int [56];
  46
  47                 public Random ()
  48                         : this (Environment.TickCount)
  49                 {
  50                 }
  51
  52                 public Random (int Seed)
  53                 {
  54                         int ii;
  55                         int mj, mk;
  56
  57                         // Numerical Recipes in C online @ http://www.library.cornell.edu/nr/bookcpdf/c7-1.pdf
  58                         mj = MSEED - Math.Abs (Seed);
  59                         SeedArray [55] = mj;
  60                         mk = 1;
  61                         for (int i = 1; i < 55; i++) {  //  [1, 55] is special (Knuth)
  62                                 ii = (21 * i) % 55;
  63                                 SeedArray [ii] = mk;
  64                                 mk = mj - mk;
  65                                 if (mk < 0)
  66                                         mk += MBIG;
  67                                 mj = SeedArray [ii];
  68                         }
  69                         for (int k = 1; k < 5; k++) {
  70                                 for (int i = 1; i < 56; i++) {
  71                                         SeedArray [i] -= SeedArray [1 + (i + 30) % 55];
  72                                         if (SeedArray [i] < 0)
  73                                                 SeedArray [i] += MBIG;
  74                                 }
  75                         }
  76                         inext = 0;
  77                         inextp = 31;
  78                 }
  79
  80                 protected virtual double Sample ()
  81                 {
  82                         int retVal;
  83
  84                         if (++inext  >= 56) inext  = 1;
  85                         if (++inextp >= 56) inextp = 1;
  86
  87                         retVal = SeedArray [inext] - SeedArray [inextp];
  88
  89                         if (retVal < 0)
  90                                 retVal += MBIG;
  91
  92                         SeedArray [inext] = retVal;
  93
  94                         return retVal * (1.0 / MBIG);
  95                 }
  96
  97                 public virtual int Next ()
  98                 {
  99                         return (int)(Sample () * int.MaxValue);
 100                 }
 101
 102                 public virtual int Next (int maxValue)
 103                 {
 104                         if (maxValue < 0)
 105                                 throw new ArgumentOutOfRangeException(Locale.GetText (
 106                                         "Max value is less then min value."));
 107
 108                         return (int)(Sample () * maxValue);
 109                 }
 110
 111                 public virtual int Next (int minValue, int maxValue)
 112                 {
 113                         if (minValue > maxValue)
 114                                 throw new ArgumentOutOfRangeException (Locale.GetText (
 115                                         "Min value is greater then max value."));
 116
 117                         uint diff = (uint)(maxValue - minValue);
 118                         if (diff == 0)
 119                                 return minValue;
 120
 121                         int result = (int)(Sample () * diff + minValue);
 122                         return ((result != maxValue) ? result : (result - 1));
 123                 }
 124
 125                 public virtual void NextBytes (byte [] buffer)
 126                 {
 127                         if (buffer == null)
 128                                 throw new ArgumentNullException ("buffer");
 129
 130                         for (int i = 0; i < buffer.Length; i++) {
 131                                 buffer [i] = (byte)(Sample () * (byte.MaxValue + 1));
 132                         }
 133                 }
 134
 135                 public virtual double NextDouble ()
 136                 {
 137                         return this.Sample ();
 138                 }
 139         }
 140 }