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High resolution date and time class
By Håkan Trygg

A high resolution time class that is a replacement for COleDateTime that does not use MFC.

	VC6, Win9x, NT4
	Posted 18 Jan 2000
	Updated 25 Jan 2000
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Overview

The CHighTime and CHighTimeSpan are two classes for replacement of COleDateTime and COleDateTimeSpan. Instead of using a double for storing the date, it uses a 64 bit integer to store the date and time. The range is +/-29000 years and the smallest time span is 0.1 microseconds.

Background

As "everybody" knows that accuracy of floating point is not so good with small values. My experience says COleDateTime(Span) can not handle 1 second time and spans correctly. Sometimes I would get: (2sec-1sec) != 1sec ... This was not what I wanted!

Secondly, the resolution for COleDateTime is only 1 second and I needed better. CHighTime(Span) handle down to 0.1 microsecond. I choose this because FILETIME and the KeQuerySystemTime function in the kernel use this resolution. One strange thing is that they have zero time at January 1, 1601. But I follow that convention for easy integration.

Finally, I needed to calculate time in a kernel driver and there floating point maths not possible. There are some changes that are needed to do before it is possible to use it in a driver. All MFC use must be also removed. I have started but haven't finished it. It should also be possible to use the classes in a non MFC project with some small not yet implemented parts...See below

To use

Using CHighTime(Span) is quite simple and similar to COleDateTime(Span). Include CHighTime.h where you need it and create an instance of CHighTime. There are some different constructors. Both with separate date/time parts and with COleDateTime or SYSTEMTIME or FILETIME as arguments. The output format string is the same as for COleDateTime(Span).Format and _tcsftime with additional codes for millisec(%s), microsec(%u), nanosec(%n).

CHighTimeSpan is also capable of handling "out of range" values. eg. 30 hours = > 1 day + 6 hours

The constructors have milli, micro, nano default value 0 so it is possible to replace COleDateTime directly without any changes.

CHighTime PresentTime, SomeTime;
CHighTimeSpan TheLife, OneDay(1,0,0,0);
CString sText;
SYSTEMTIME systime;

PresentTime = CHighTime::GetPresentTime();
SomeTime = CHighTime(1968, 6, 8, 0, 2, 0);
TheLife = PresentTime - SomeTime;
sText = TheLife.Format("I have lived %D days %H hours %M minutes %S seconds %s milliseconds\n");
AfxMessageBox(sText);
systime = CHighTime(2000,1,13, 14,07,10, 20, 40, 100);
SomeTime.SetDateTime(2000, 1, 13, 14, 25, 10);
sText.Format("The time now is %s\n", (LPCTSTR)PresentTime.Format("%H:%M:%S:%s"));
sText.Format("The date tomorrow is %s\n", (LPCTSTR)(PresentTime+OneDay).Format("%Y:%m:%d"));

If you want to use the class in a MFC project, add #include "stdafx.h" before the include of hightime.h, in the hightime.cpp like this.

#include "stdafx.h"
#include "hightime.h"

Things to improve

Modify so a kerneldriver can use the classes. The string functions must be removed/changed. The only need for the CHighTime::Format function should be for trace. So why make that work for almost nothing....??? A additional #define could be used for using the classes in a driver

Please feel free to send me any suggestions about these classes.

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