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Use GetSystemTimeAsFileTime to implement gettimeofday on win32.

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It is (in my benchmarks) way faster than _ftime, though the
conversion process is not so straightforward.  In theory, it can
have a better granularity too, though in practice who knows what
you're getting.
This commit is contained in:
Nick Mathewson 2010-09-02 17:52:20 -04:00
parent 04ba27ebf2
commit b8b8aa560c
1 changed files with 28 additions and 13 deletions
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41
evutil.c
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@ -364,26 +364,41 @@ evutil_strtoll(const char *s, char **endptr, int base)
}
#ifndef _EVENT_HAVE_GETTIMEOFDAY
/* No gettimeofday; this muse be windows. */
/* No gettimeofday; this must be windows. */
int
evutil_gettimeofday(struct timeval *tv, struct timezone *tz)
{
struct _timeb tb;
#ifdef _MSC_VER
#define U64_LITERAL(n) n##ui64
#else
#define U64_LITERAL(n) n##llu
#endif
/* Conversion logic taken from Tor, which in turn took it
* from Perl. GetSystemTimeAsFileTime returns its value as
* an unaligned (!) 64-bit value containing the number of
* 100-nanosecond intervals since 1 January 1601 UTC. */
#define EPOCH_BIAS U64_LITERAL(116444736000000000)
#define UNITS_PER_SEC U64_LITERAL(10000000)
#define USEC_PER_SEC U64_LITERAL(1000000)
#define UNITS_PER_USEC U64_LITERAL(10)
union {
FILETIME ft_ft;
ev_uint64_t ft_64;
} ft;
if (tv == NULL)
return -1;
/* XXXX
* _ftime is not the greatest interface here; GetSystemTimeAsFileTime
* would give us better resolution, whereas something cobbled together
* with GetTickCount could maybe give us monotonic behavior.
*
* Either way, I think this value might be skewed to ignore the
* timezone, and just return local time. That's not so good.
*/
_ftime(&tb);
tv->tv_sec = (long) tb.time;
tv->tv_usec = ((int) tb.millitm) * 1000;
GetSystemTimeAsFileTime(&ft.ft_ft);
if (EVUTIL_UNLIKELY(ft.ft_64 < EPOCH_BIAS)) {
/* Time before the unix epoch. */
return -1;
}
ft.ft_64 -= EPOCH_BIAS;
tv->tv_sec = (long) (ft.ft_64 / UNITS_PER_SEC);
tv->tv_usec = (long) ((ft.ft_64 / UNITS_PER_USEC) % USEC_PER_SEC);
return 0;
}
#endif