From: gthall AT icg DOT tu-graz DOT ac DOT at ("Gerhard G. Thallinger")
Subject: Re: High resolution clock
4 Aug 1997 10:39:38 -0700
Approved: cygnus DOT gnu-win32 AT cygnus DOT com
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Message-ID: <Pine.SGI.3.95.970804182011.4969B-100000.cygnus.gnu-win32@fcggsg22.icg.tu-graz.ac.at>
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On Fri, 25 Jul 1997, Joerg Lepler wrote:

> 
> Hi,
> 
> Does anyone know about such clock functions for the win32 environment?
> 
There is the (undocumented) function NtQueryPerformanceCounter which
returns a 64 bit counter value and the frequency of the counter update.

I use this function on a Everex Dual Pentium Pro with 200 MHz. On this
computer the call to this function takes about 14 microseconds and the
counter has a resolution of 5 ns (= 1 / 200 MHz).  
On single processor machines calls may take significantly longer and
the resolution is much less, so your mileage may vary. See the recent
discussion on comp.os.ms-windows.programmer.nt.kernel-mode for details.

I attach an example how to use this function.

BTW: Which functions did you use on SUN and SGI ?

HTH

Gerhard G. Thallinger
Vexcel Imaging GmbH

---------------------------Start of program profile.c -------------------------
/*
 * This code is supplied 'as is', no warranty whatsoever implied.
 * Use at your own risk.
 */

#include <stdio.h>
#include <stdlib.h>

#include <windows.h>

typedef LONG NTSTATUS;
typedef NTSTATUS WINBASEAPI (WINAPI *NtQPC)(LARGE_INTEGER* pCounter,
                                            LARGE_INTEGER* pFrequency);

#undef __FUNC__
#define __FUNC__ "GetFuncAddress()"
NtQPC GetFuncAddress()
{
   NtQPC pTemp = NULL;
   NTSTATUS result = 0;
   int loadLib = 0;
   HMODULE hNtDll = NULL;

   hNtDll = GetModuleHandle("ntdll");
   if (hNtDll == NULL) {
      hNtDll = LoadLibrary("ntdll");
      loadLib = 1;
   }
   if (hNtDll != NULL) {
      pTemp = (NtQPC) GetProcAddress(hNtDll, "NtQueryPerformanceCounter");
      if (loadLib != 0) {
         FreeLibrary(hNtDll);
      }
   }
   return(pTemp);
}

#undef __FUNC__
#define __FUNC__ "main()"
main(int argc, char* argv[])
{
   NTSTATUS       result = 0;
   int            iLoop;
   LARGE_INTEGER  llCount;
   LARGE_INTEGER  llFrequency;
   NtQPC          NtQueryPerformanceCounter = NULL;

   NtQueryPerformanceCounter = GetFuncAddress();
   if (NtQueryPerformanceCounter != NULL) {
      for (iLoop = 0; iLoop < 1000000;iLoop++) {
         result = NtQueryPerformanceCounter(&llCount,&llFrequency);
      }
   } else {
      fprintf(stderr,"Could not determine function address");
   }
   return(0);
}
---------------------------End   of program profile.c -------------------------



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