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Date: Wed, 23 Jan 2002 14:03:35 -0500
From: Christopher Faylor <cgf AT redhat DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: gettimeofday() does not returns usec resolution
Message-ID: <20020123190335.GC18042@redhat.com>
Reply-To: cygwin AT cygwin DOT com
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References: <00af01c1a3de$7af04b40$60a407d5 AT BRAMSCHE> <3C4E6FD1 DOT 9060505 AT computer DOT org> <20020123172718 DOT GE6765 AT redhat DOT com> <3C4F01DF DOT 70AA4F00 AT lapo DOT it>
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On Wed, Jan 23, 2002 at 07:33:04PM +0100, Lapo Luchini wrote:
>> >> Has anyone address this problem already. I have looked int the
>> >> cygwin and list and found the only topic
>> >http://sources.redhat.com/ml/cygwin/2001-12/msg00201.html
>
>In the attached file there is a "patch" for gettmieofday:

Hmm.  I do remember this patch.  Can you submit this to cygwin-patches
in the correct format: http://cygwin.com/contrib.html ?

Do you have an assignment on file with Red Hat?

cgf

>-------
>int gettimeofday(struct timeval *tv, struct timezone *tz)
>{
> LARGE_INTEGER   t;
> FILETIME   f;
> double     microseconds;
> static LARGE_INTEGER offset;
> static double   frequencyToMicroseconds;
> static int    initialized = 0;
> static BOOL    usePerformanceCounter = 0;
>
> if (!initialized) {
>  LARGE_INTEGER performanceFrequency;
>  initialized = 1;
>  usePerformanceCounter = QueryPerformanceFrequency(&performanceFrequency);
>  if (usePerformanceCounter) {
>   QueryPerformanceCounter(&offset);
>   frequencyToMicroseconds = (double)performanceFrequency.QuadPart /
>1000000.;
>  } else {
>   offset = getFILETIMEoffset();
>   frequencyToMicroseconds = 10.;
>  }
> }
> if (usePerformanceCounter) QueryPerformanceCounter(&t);
> else {
>  GetSystemTimeAsFileTime(&f);
>  t.QuadPart = f.dwHighDateTime;
>  t.QuadPart <<= 32;
>  t.QuadPart |= f.dwLowDateTime;
> }
>
> t.QuadPart -= offset.QuadPart;
> microseconds = (double)t.QuadPart / frequencyToMicroseconds;
> t.QuadPart = microseconds;
> tv->tv_sec = t.QuadPart / 1000000;
> tv->tv_usec = t.QuadPart % 1000000;
> return (0);
>}
>------------
>
>The following Microsoft page (
>http://www.vbapi.com/ref/q/queryperformancecounter.html ) says it supported
>on all version (startig from NT3.51 and Windows95) an, at least, it calls
>GetTickCount()*1000.
>
>> >> In http://www-106.ibm.com/developerworks/library/l-rt1/ there is a
>> >> detailed instruction how to use the hugh resolution counter. .
>> >>
>> >> $ cat timeofday.c #include <sys/time.h>
>> >>
>> >> int main() { struct timeval tp; long a,b;
>> >>
>> >> gettimeofday(&tp,0); a =
>> >> ((unsigned)tp.tv_sec)*1000000+((unsigned)tp.tv_usec);
>> >>
>> >> printf("timestamp (us): %d\n",a); usleep(1000); gettimeofday(&tp,0); b
>> >>  = ((unsigned)tp.tv_sec)*1000000+((unsigned)tp.tv_usec);
>> >printf("timestamp
>> >>  (us): %d (diff) %d\n",b,b-a); }
>
>I adapted the code to find exactly the minimum time slice, and not "how well
>1ms of retard is seen" (it was a 0ns or 15000ns, this is always 15000ns;
>moreover printf is out of the "timing" section):
>
>-------
>#include <sys/time.h>
>#define TV2LONG(t) ((unsigned long)t.tv_sec)*1000000+((unsigned
>long)t.tv_usec)
>int main() {
> struct timeval tp;
> unsigned long a, b;
> unsigned int n = 1;
> for(n=1; n<=20; n++) {
>  gettimeofday(&tp, 0);
>  a = TV2LONG(tp);
>  do {
>   gettimeofday(&tp, 0);
>  } while((b = TV2LONG(tp)) <= a);
>  printf("try %2d: %ld - %ld = %ld\n", n, a, b, b-a);
> }
>}
>-------
>
>> Was there a patch submitted for this for cygwin?
>
>Well, sort of, as said in the first paragraph of this reply =)
>
>> If I missed it, I apologize.  Otherwise, since this issue is of zero
>> importance to me
>
>I am a little of a maniac indeed, and I'd like to have that patch applied
>(even if I don't think I need nano performance anytime soon ^_^) if that's
>not a problem. I could also volunteer to make the patch but... I think it's
>just amatter of cut-n-paste from Tmi Prince's message (or from this one).
>
>--
>Lapo 'Raist' Luchini
>lapo AT lapo DOT it (PGP & X.509 keys available)
>http://www.lapo.it (ICQ UIN: 529796)
>
>
>
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