guids

SequentialGuid.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace Guids
{
    public static class SequentialGuid
    {
        [DllImport("rpcrt4.dll", SetLastError = true)]
        private static extern int UuidCreateSequential(out Guid guid);

        public static Guid NewGuid()
        {
            Guid newGuid;
            int returnVal = UuidCreateSequential(out newGuid);

            if (returnVal != 0)
                throw new Exception("UuidCreateSequential failed with exit code " + returnVal);

            return newGuid;
        }

        public static Guid NewSqlServerFormattedGuid()
        {
            byte[] bytes = NewGuid().ToByteArray();

            CopyBigEndianBytes(BitConverter.ToInt32(bytes, 0), 4, bytes, 0);
            CopyBigEndianBytes(BitConverter.ToInt16(bytes, 4), 2, bytes, 4);
            CopyBigEndianBytes(BitConverter.ToInt16(bytes, 6), 2, bytes, 6);

            return new Guid(bytes);
        }

        // Tak til Jon Skeet http://www.yoda.arachsys.com/csharp/miscutil

        private static void CopyBigEndianBytes(long value, int bytes, byte[] buffer, int index)
        {
            int endOffset = index + bytes - 1;
            for (int i = 0; i < bytes; i++)
            {
                buffer[endOffset - i] = unchecked((byte) (value & 0xff));
                value = value >> 8;
            }
        }
    }
}

TimeGuid.cs

using System.Diagnostics;
using System.Threading.Tasks;
using System.Text;
using System.Collections.Generic;
using System;
using System.Linq;

namespace Guids
{
    public class TimeGuid
    {
        public static Guid NewTimeGuid()
        {
            var resultBytes = new byte[16];

            byte[] guidBytes = Guid.NewGuid().ToByteArray();

            long time = DateTime.UtcNow.Ticks;
            Debug.WriteLine(time);
            byte[] timeBytes = BitConverter.GetBytes(time);
            byte[] timeBytesReversed = timeBytes.Reverse().ToArray();

            // the last 6 bytes are most significant, and to be sorted properly, the time bytes need to be reversed
            Buffer.BlockCopy(guidBytes, 0, resultBytes, 0, 10); // first 10 bytes are from GUID
            Buffer.BlockCopy(timeBytesReversed, 0, resultBytes, 10, 6); // last 6 bytes are from time

            var result = new Guid(resultBytes);
            return result;
        }
    }
}