There’s a Windows function to create sequential GUIDs, called

UuidCreateSequential http://msdn.microsoft.com/en-us/library/windows/desktop/aa379322(v=vs.85).aspx

But SQL Server uses a different sort order for GUIDs, and the results of UuidCreateSequential  are not sequential with respect to SQL Server’s sort order.  To make them sequential SQL Server’s internal NEWSEQUENTIALID function performs some byte shuffling on the GUID.

NEWSEQUENTIALID http://msdn.microsoft.com/en-us/library/ms189786.aspx

If you want to generate sequential GUIDs in application code you need to perform the same byte shuffling.  I compared the output of UuidCreateSequentiald and NEWSEQUENTIALID  to come up with the mapping and the following C# function that uses UuidCreateSequential to generate GUIDs that are sequential according to SQL Server’s GUID sort order:

  public class SQLGuidUtil

  {

      [DllImport("rpcrt4.dll", SetLastError = true)]

      static extern int UuidCreateSequential(out Guid guid);

 

      public static Guid NewSequentialId()

      {

        Guid guid;

        UuidCreateSequential(out guid);

        var s = guid.ToByteArray();

        var t = new byte[16];

        t[3] = s[0];

        t[2] = s[1];

        t[1] = s[2];

        t[0] = s[3];

        t[5] = s[4];

        t[4] = s[5];

        t[7] = s[6];

        t[6] = s[7];

        t[8] = s[8];

        t[9] = s[9];

        t[10] = s[10];

        t[11] = s[11];

        t[12] = s[12];

        t[13] = s[13];

        t[14] = s[14];

        t[15] = s[15];

        return new Guid(t);

      }

  }