Use This Higher-Resolution Stopwatch

Use This Higher-Resolution Stopwatch

Use this code to create a class called HiResTimer:

 'The number is codified as HighPart*2^32+LowPartPrivate Type LARGE_INTEGER	LowPart As Long	HighPart As LongEnd TypePrivate Declare Function QueryPerformanceCounter Lib _	"kernel32" (lpPerformanceCount As LARGE_INTEGER) _	As LongPrivate Declare Function QueryPerformanceFrequency Lib _	"kernel32" (lpFrequency As LARGE_INTEGER) As LongPrivate m_TicksPerSecond As DoublePrivate m_LI0 As LARGE_INTEGERPrivate m_LI1 As LARGE_INTEGERFriend Sub Class_Initialize()	Dim LI As LARGE_INTEGER	If QueryPerformanceFrequency(LI) <> 0 Then		m_TicksPerSecond = LI2Double(LI)	Else		m_TicksPerSecond = -1	End IfEnd SubFriend Property Get Resolution() As Double	Resolution = 1# / m_TicksPerSecondEnd PropertyFriend Sub EnterBlock()	QueryPerformanceCounter m_LI0End SubFriend Sub ExitBlock()	QueryPerformanceCounter m_LI1End SubFriend Property Get ElapsedTime() As Double	Dim EnterTime As Double, ExitTime As Double	EnterTime = LI2Double(m_LI0) / m_TicksPerSecond	ExitTime = LI2Double(m_LI1) / m_TicksPerSecond	ElapsedTime = ExitTime - EnterTimeEnd PropertyFriend Function LI2Double(LI As LARGE_INTEGER) As Double	Dim Low As Double	Const TWO_32 = 4# * 1024# * 1024# * 1024#	Low = LI.LowPart	If Low < 0 Then Low = Low + TWO_32		'Now Low is in the range 0...2^32-1		LI2Double = LI.HighPart * TWO_32 + LowEnd Function

Here's an example of the HiResTimer in use:

 Dim hrt As HiResTimer, d As DoubleSet hrt = New HiResTimerDebug.Assert hrt.Resolution > 0MsgBox "Resolution [usecs]:" & hrt.Resolution * 1000000#hrt.EnterBlockhrt.ExitBlockMsgBox "Call overhead [usecs]:" & hrt.ElapsedTime * _	1000000#hrt.EnterBlockd = 355# / 113#hrt.ExitBlockMsgBox "Elapsed Time [usecs]:" & hrt.ElapsedTime * _	1000000#

Believe it or not, you can time even native-compiled code division. For more information, look at the MSDN Library description of the kernel APIs used here. On x86 architectures, resolution is better that 1 microsecond. Be careful, however, of trusting single instance timings, as you'll find the "resolution" of this performance counter varies over time. In fact, the overhead of simply calling QueryPerformanceCounter in VB is quite a measurable time period itself.

Although you can time single operations, you're still better off averaging the time required for hundreds or thousands of similar operations.

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