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ITS#5668 avoid overflows in Windows microsecond computation

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This commit is contained in:
Howard Chu 2008-09-11 01:51:02 +00:00
parent ca62039424
commit 178141d7ec
1 changed files with 28 additions and 17 deletions
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45
libraries/liblutil/utils.c
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@ -303,23 +303,6 @@ lutil_gettime( struct lutil_tm *tm )
GetSystemTime( &st );
QueryPerformanceCounter( &count );
/* We assume Windows has at least a vague idea of
* when a second begins. So we align our microsecond count
* with the Windows millisecond count using this offset.
* We retain the submillisecond portion of our own count.
*/
if ( !cFreq.QuadPart ) {
long long t;
int usec;
QueryPerformanceFrequency( &cFreq );
t = count.QuadPart * 1000000;
t /= cFreq.QuadPart;
usec = t % 10000000;
usec /= 1000;
offset = ( usec - st.wMilliseconds ) * 1000;
}
/* It shouldn't ever go backwards, but multiple CPUs might
* be able to hit in the same tick.
*/
@ -330,14 +313,42 @@ lutil_gettime( struct lutil_tm *tm )
prevCount = count;
}
/* We assume Windows has at least a vague idea of
* when a second begins. So we align our microsecond count
* with the Windows millisecond count using this offset.
* We retain the submillisecond portion of our own count.
*
* Note - this also assumes that the relationship between
* the PerformanceCouunter and SystemTime stays constant;
* that assumption breaks if the SystemTime is adjusted by
* an external action.
*/
if ( !cFreq.QuadPart ) {
long long t;
int usec;
QueryPerformanceFrequency( &cFreq );
/* just get sub-second portion of counter */
t = count.QuadPart % cFreq.QuadPart;
/* convert to microseconds */
t *= 1000000;
usec = t / cFreq.QuadPart;
offset = usec - st.wMilliseconds * 1000;
}
tm->tm_usub = subs;
/* convert to microseconds */
count.QuadPart %= cFreq.QuadPart;
count.QuadPart *= 1000000;
count.QuadPart /= cFreq.QuadPart;
count.QuadPart -= offset;
tm->tm_usec = count.QuadPart % 1000000;
if ( tm->tm_usec < 0 )
tm->tm_usec += 1000000;
/* any difference larger than microseconds is
* already reflected in st