Net中随机函数的算法

以前写程序的时候，经常用到随机函数。不过也就事随手拿了一用完成目的而已。不知道今天怎么了特别想看看随机函数的算法是怎么回事。于是结合

http://dotnet.di.unipi.it/Content/sscli/docs/doxygen/fx/bcl/random_8cs-source.html

归纳了一下：

using System;

    class MyRnd
    ...{
        private const int MBIG = Int32.MaxValue;
        private const int MSEED = 161803398;
        private const int MZ = 0;
        private int inext, inextp;
        private int[] SeedArray = new int[56];


        public MyRnd()
            : this(Environment.TickCount)
        //一个 32 位带符号整数，它包含自上次启动计算机以来所经过的时间（以毫秒为单位）。
        ...{
        }
      

        public MyRnd(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;
        }

        //产生0~1的double数
        protected virtual double Sample()
        ...{
            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 * (1.0 / MBIG));
        }

        public virtual double NextDouble()
        ...{
            return Sample();
        }

         public virtual int Next(int minValue, int maxValue) ...{
           if (minValue>maxValue) ...{
               throw new ArgumentOutOfRangeException("Argument_MinMaxValue");
           }

           int range = (maxValue-minValue);
    
           //This is the case where we flipped around (e.g. MaxValue-MinValue);
           if (range<0) ...{
               long longRange = (long)maxValue-(long)minValue;
               return (int)(((long)(Sample()*((double)longRange)))+minValue);
           }
          
           return ((int)(Sample()*(range)))+minValue;
       }
    }

使用方法：

static void Main(string[] args)
        ...{
            MyRnd r = new MyRnd();
            Console.WriteLine(r.NextDouble().ToString());
            Console.Read();
        }