using System;

​

public class Program

{

    const int YEAR_ORIGIN = 2000;

    const int ID_MAX = 2097151;  // 2 ^ 21 - 1;

​

    public static void Main()

    {

        /*          max     bits    offset (random bits at lower/upper)

            year    127     7       57 / 36

            day/yr  366     9       48 / 27     or month(4) + day(5)

            hour    23      5       43 / 22

            minute  59      6       37 / 16

            second  59      6       31 / 10

            ms      999     10      21 /  0

            random          21       0 / 43     range: 0 to 2,097,151

        */

​

        var rng = new Random();

        var now = DateTime.UtcNow;

​

        // randomize lower bits.

        long id = (long)(now.Year - YEAR_ORIGIN) << 57;

        id |= (long)now.Month << 53;

        id |= (long)now.Day << 48;

        //id |= (long)now.DayOfYear << 48;

        id |= (long)now.Hour << 43;

        id |= (long)now.Minute << 37;

        id |= (long)now.Second << 31;

        id |= (long)now.Millisecond << 21;

        id |= rng.Next(0, ID_MAX);

        Console.WriteLine("random lower: " + id.ToString("X2") + ": " + id);

​

        // randomize upper bits.

        id = (long)(now.Year - YEAR_ORIGIN) << 36;

        id |= (long)now.Month << 32;

        id |= (long)now.Day << 27;

        //id |= (long)now.DayOfYear << 27;

        id |= (long)now.Hour << 22;

        id |= (long)now.Minute << 16;

        id |= (long)now.Second << 10;

        id |= (long)now.Millisecond;

        id |= ((long)rng.Next(0, ID_MAX)) << 43;

        Console.WriteLine("random upper: " + id.ToString("X2") + ": " + id);

​

​

        // set sign bit.

        id |= long.MinValue;  // 0x80L << 56;

        Console.WriteLine("set sign bit: " + id.ToString("X2") + ": " + id);

​

        // remove sign bit.

        id &= ~long.MinValue;

        Console.WriteLine(" no sign bit: " + id.ToString("X2") + ": " + id);

    }

}

​