随机long(Random long/NextLong)

 在.net FCL中random没有生成long类型的随机数,不过random可以生成0-1的随机数,这就可以帮助实现random Long.

如下为一简单实现(.net 3.5):

 1     static class Common
 2     {
 3         public static long NextLong(this Random random,long minValue,long maxValue)
 4         {
 5             if (minValue > maxValue)
 6             {
 7                 throw new ArgumentException("minValue is great than maxValue", "minValue");
 8             }
 9             long num = maxValue - minValue;
10             return minValue + (long) (random.NextDouble() * num);
11         }
12     }

 使用如下:

 Random random = new Random();
2 random.NextLong(MinSize, MaxSize);

由于random.NextDouble() 是根据Int32来生成的，其个数为Int32.Max个。如果上述NextLong连续调用maxValue-minValue+1次,在maxValue-minValue+1 > Int32.Max时,未必能生成所有可能近视分布均匀的随机数据。

现 更新如下:

public static long NextLong(this Random random, long min, long max)
        {
            byte[] minArr = BitConverter.GetBytes(min);
            int hMin = BitConverter.ToInt32(minArr, 4);
            int lMin = BitConverter.ToInt32(new byte[] { minArr[0], minArr[1], minArr[2], minArr[3] }, 0);

            byte[] maxArr = BitConverter.GetBytes(max);
            int hMax = BitConverter.ToInt32(maxArr, 4);
            int lMax = BitConverter.ToInt32(new byte[] { maxArr[0], maxArr[1], maxArr[2], maxArr[3] }, 0);

            if (random == null)
            {
                random = new Random();
            }

            int h = random.Next(hMin, hMax);
            int l = 0;
            if (h == hMin)
            {
                l = random.Next(Math.Min(lMin, lMax), Math.Max(lMin, lMax));
            }
            else
            {
                l = random.Next(0, Int32.MaxValue);
            }
            
            byte[] lArr = BitConverter.GetBytes(l);
            byte[] hArr = BitConverter.GetBytes(h);
            byte[] result = new byte[8];

            for (int i = 0; i < lArr.Length; i++)
            {
                result[i] = lArr[i];
                result[i + 4] = hArr[i];
            }
            return BitConverter.ToInt64(result, 0);
        }