Source code of Windows XP (NT5)
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/***
*ftime64.c - return system time
*
* Copyright (c) 1998-2001, Microsoft Corporation. All rights reserved.
*
*Purpose:
* Returns the system date/time in a structure form.
*
*Revision History:
* 05-22-98 GJF Created.
*
*******************************************************************************/
#include <cruntime.h>
#include <sys/types.h>
#include <sys/timeb.h>
#include <time.h>
#include <msdos.h>
#include <dos.h>
#include <stdlib.h>
#include <windows.h>
#include <internal.h>
/*
* Number of 100 nanosecond units from 1/1/1601 to 1/1/1970
*/
#define EPOCH_BIAS 116444736000000000i64
/*
* Union to facilitate converting from FILETIME to unsigned __int64
*/
typedef union {
unsigned __int64 ft_scalar;
FILETIME ft_struct;
} FT;
/*
* Cache for the minutes count for with DST status was last assessed
*/
static __time64_t elapsed_minutes_cache;
/*
* Three values of dstflag_cache
*/
#define DAYLIGHT_TIME 1
#define STANDARD_TIME 0
#define UNKNOWN_TIME -1
/*
* Cache for the last determined DST status
*/
static int dstflag_cache = UNKNOWN_TIME;
/***
*void _ftime(timeptr) - return DOS time in a structure
*
*Purpose:
* returns the current DOS time in a struct timeb structure
*
*Entry:
* struct timeb *timeptr - structure to fill in with time
*
*Exit:
* no return value -- fills in structure
*
*Exceptions:
*
*******************************************************************************/
_CRTIMP void __cdecl _ftime64 (
struct __timeb64 *tp
)
{
FT nt_time;
__time64_t t;
TIME_ZONE_INFORMATION tzinfo;
DWORD tzstate;
__tzset();
tp->timezone = (short)(_timezone / 60);
GetSystemTimeAsFileTime( &(nt_time.ft_struct) );
/*
* Obtain the current DST status. Note the status is cached and only
* updated once per minute, if necessary.
*/
if ( (t = (__time64_t)(nt_time.ft_scalar / 600000000i64))
!= elapsed_minutes_cache )
{
if ( (tzstate = GetTimeZoneInformation( &tzinfo )) != 0xFFFFFFFF )
{
/*
* Must be very careful in determining whether or not DST is
* really in effect.
*/
if ( (tzstate == TIME_ZONE_ID_DAYLIGHT) &&
(tzinfo.DaylightDate.wMonth != 0) &&
(tzinfo.DaylightBias != 0) )
dstflag_cache = DAYLIGHT_TIME;
else
/*
* When in doubt, assume standard time
*/
dstflag_cache = STANDARD_TIME;
}
else
dstflag_cache = UNKNOWN_TIME;
elapsed_minutes_cache = t;
}
tp->dstflag = (short)dstflag_cache;
tp->millitm = (unsigned short)((nt_time.ft_scalar / 10000i64) %
1000i64);
tp->time = (__time64_t)((nt_time.ft_scalar - EPOCH_BIAS) / 10000000i64);
}