path: root/win/tclWinTime.c

/*
 * tclWinTime.c --
 *
 *	Contains Windows specific versions of Tcl functions that obtain time
 *	values from the operating system.
 *
 * Copyright 1995-1998 by Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include "tclInt.h"

#define SECSPERDAY	(60L * 60L * 24L)
#define SECSPERYEAR	(SECSPERDAY * 365L)
#define SECSPER4YEAR	(SECSPERYEAR * 4L + SECSPERDAY)

/*
 * Number of samples over which to estimate the performance counter.
 */

#define SAMPLES		64

/*
 * The following arrays contain the day of year for the last day of each
 * month, where index 1 is January.
 */

static const int normalDays[] = {
    -1, 30, 58, 89, 119, 150, 180, 211, 242, 272, 303, 333, 364
};

static const int leapDays[] = {
    -1, 30, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365
};

typedef struct {
    char tzName[64];		/* Time zone name */
    struct tm tm;		/* time information */
} ThreadSpecificData;
static Tcl_ThreadDataKey dataKey;

/*
 * Data for managing high-resolution timers.
 */

typedef struct {
    CRITICAL_SECTION cs;	/* Mutex guarding this structure. */
    int initialized;		/* Flag == 1 if this structure is
				 * initialized. */
    int perfCounterAvailable;	/* Flag == 1 if the hardware has a performance
				 * counter. */
    HANDLE calibrationThread;	/* Handle to the thread that keeps the virtual
				 * clock calibrated. */
    HANDLE readyEvent;		/* System event used to trigger the requesting
				 * thread when the clock calibration procedure
				 * is initialized for the first time. */
    HANDLE exitEvent; 		/* Event to signal out of an exit handler to
				 * tell the calibration loop to terminate. */
    LARGE_INTEGER nominalFreq;	/* Nominal frequency of the system performance
				 * counter, that is, the value returned from
				 * QueryPerformanceFrequency. */

    /*
     * The following values are used for calculating virtual time. Virtual
     * time is always equal to:
     *    lastFileTime + (current perf counter - lastCounter)
     *				* 10000000 / curCounterFreq
     * and lastFileTime and lastCounter are updated any time that virtual time
     * is returned to a caller.
     */

    ULARGE_INTEGER fileTimeLastCall;
    LARGE_INTEGER perfCounterLastCall;
    LARGE_INTEGER curCounterFreq;

    /*
     * Data used in developing the estimate of performance counter frequency
     */

    Tcl_WideUInt fileTimeSample[SAMPLES];
				/* Last 64 samples of system time. */
    Tcl_WideInt perfCounterSample[SAMPLES];
				/* Last 64 samples of performance counter. */
    int sampleNo;		/* Current sample number. */
} TimeInfo;

static TimeInfo timeInfo = {
    { NULL, 0, 0, NULL, NULL, 0 },
    0,
    0,
    (HANDLE) NULL,
    (HANDLE) NULL,
    (HANDLE) NULL,
#ifdef HAVE_CAST_TO_UNION
    (LARGE_INTEGER) (Tcl_WideInt) 0,
    (ULARGE_INTEGER) (DWORDLONG) 0,
    (LARGE_INTEGER) (Tcl_WideInt) 0,
    (LARGE_INTEGER) (Tcl_WideInt) 0,
#else
    0,
    0,
    0,
    0,
#endif
    { 0 },
    { 0 },
    0
};

/*
 * Declarations for functions defined later in this file.
 */

static struct tm *	ComputeGMT(const time_t *tp);
static void		StopCalibration(ClientData clientData);
static DWORD WINAPI	CalibrationThread(LPVOID arg);
static void 		UpdateTimeEachSecond(void);
static void		ResetCounterSamples(Tcl_WideUInt fileTime,
			    Tcl_WideInt perfCounter, Tcl_WideInt perfFreq);
static Tcl_WideInt	AccumulateSample(Tcl_WideInt perfCounter,
			    Tcl_WideUInt fileTime);
static void		NativeScaleTime(Tcl_Time* timebuf,
			    ClientData clientData);
static Tcl_WideInt	NativeGetMicroseconds(void);
static void		NativeGetTime(Tcl_Time* timebuf,
			    ClientData clientData);

/*
 * TIP #233 (Virtualized Time): Data for the time hooks, if any.
 */

Tcl_GetTimeProc *tclGetTimeProcPtr = NativeGetTime;
Tcl_ScaleTimeProc *tclScaleTimeProcPtr = NativeScaleTime;
ClientData tclTimeClientData = NULL;

/*
 *----------------------------------------------------------------------
 *
 * TclpGetSeconds --
 *
 *	This procedure returns the number of seconds from the epoch. On most
 *	Unix systems the epoch is Midnight Jan 1, 1970 GMT.
 *
 * Results:
 *	Number of seconds from the epoch.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

unsigned long
TclpGetSeconds(void)
{
    Tcl_WideInt usecSincePosixEpoch;

    /* Try to use high resolution timer */
    if ( tclGetTimeProcPtr == NativeGetTime
      && (usecSincePosixEpoch = NativeGetMicroseconds())
    ) {
	return usecSincePosixEpoch / 1000000;
    } else {
	Tcl_Time t;

	tclGetTimeProcPtr(&t, tclTimeClientData);	/* Tcl_GetTime inlined. */
	return t.sec;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TclpGetClicks --
 *
 *	This procedure returns a value that represents the highest resolution
 *	clock available on the system. There are no guarantees on what the
 *	resolution will be. In Tcl we will call this value a "click". The
 *	start time is also system dependant.
 *
 * Results:
 *	Number of clicks from some start time.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

unsigned long
TclpGetClicks(void)
{
    Tcl_WideInt usecSincePosixEpoch;

    /* Try to use high resolution timer */
    if ( tclGetTimeProcPtr == NativeGetTime
      && (usecSincePosixEpoch = NativeGetMicroseconds())
    ) {
	return (unsigned long)usecSincePosixEpoch;
    } else {
	/*
	* Use the Tcl_GetTime abstraction to get the time in microseconds, as
	* nearly as we can, and return it.
	*/

	Tcl_Time now;		/* Current Tcl time */

	tclGetTimeProcPtr(&now, tclTimeClientData);	/* Tcl_GetTime inlined */
	return (unsigned long)(now.sec * 1000000) + now.usec;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TclpGetWideClicks --
 *
 *	This procedure returns a WideInt value that represents the highest
 *	resolution clock in microseconds available on the system.
 *
 * Results:
 *	Number of microseconds (from the epoch).
 *
 * Side effects:
 *	This should be used for time-delta resp. for measurement purposes
 *	only, because on some platforms can return microseconds from some
 *	start time (not from the epoch).
 *
 *----------------------------------------------------------------------
 */

Tcl_WideInt
TclpGetWideClicks(void)
{
    Tcl_WideInt usecSincePosixEpoch;

    /* Try to use high resolution timer */
    if ( tclGetTimeProcPtr == NativeGetTime
      && (usecSincePosixEpoch = NativeGetMicroseconds())
    ) {
	return usecSincePosixEpoch;
    } else {
	/*
	* Use the Tcl_GetTime abstraction to get the time in microseconds, as
	* nearly as we can, and return it.
	*/

	Tcl_Time now;

	tclGetTimeProcPtr(&now, tclTimeClientData);	/* Tcl_GetTime inlined */
	return (((Tcl_WideInt)now.sec) * 1000000) + now.usec;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetTime --
 *
 *	Gets the current system time in seconds and microseconds since the
 *	beginning of the epoch: 00:00 UCT, January 1, 1970.
 *
 * Results:
 *	Returns the current time in timePtr.
 *
 * Side effects:
 *	On the first call, initializes a set of static variables to keep track
 *	of the base value of the performance counter, the corresponding wall
 *	clock (obtained through ftime) and the frequency of the performance
 *	counter. Also spins a thread whose function is to wake up periodically
 *	and monitor these values, adjusting them as necessary to correct for
 *	drift in the performance counter's oscillator.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_GetTime(
    Tcl_Time *timePtr)		/* Location to store time information. */
{
    Tcl_WideInt usecSincePosixEpoch;

    /* Try to use high resolution timer */
    if ( tclGetTimeProcPtr == NativeGetTime
      && (usecSincePosixEpoch = NativeGetMicroseconds())
    ) {
	timePtr->sec = (long) (usecSincePosixEpoch / 1000000);
	timePtr->usec = (unsigned long) (usecSincePosixEpoch % 1000000);
    } else {
    	tclGetTimeProcPtr(timePtr, tclTimeClientData);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * NativeScaleTime --
 *
 *	TIP #233: Scale from virtual time to the real-time. For native scaling
 *	the relationship is 1:1 and nothing has to be done.
 *
 * Results:
 *	Scales the time in timePtr.
 *
 * Side effects:
 *	See above.
 *
 *----------------------------------------------------------------------
 */

static void
NativeScaleTime(
    Tcl_Time *timePtr,
    ClientData clientData)
{
    /*
     * Native scale is 1:1. Nothing is done.
     */
}

/*
 *----------------------------------------------------------------------
 *
 * NativeGetMicroseconds --
 *
 *	Gets the current system time in microseconds since the beginning
 *	of the epoch: 00:00 UCT, January 1, 1970.
 *
 * Results:
 *	Returns the wide integer with number of microseconds from the epoch, or
 *	0 if high resolution timer is not available.
 *
 * Side effects:
 *	On the first call, initializes a set of static variables to keep track
 *	of the base value of the performance counter, the corresponding wall
 *	clock (obtained through ftime) and the frequency of the performance
 *	counter. Also spins a thread whose function is to wake up periodically
 *	and monitor these values, adjusting them as necessary to correct for
 *	drift in the performance counter's oscillator.
 *
 *----------------------------------------------------------------------
 */

static Tcl_WideInt
NativeGetMicroseconds(void)
{
    /*
     * Initialize static storage on the first trip through.
     *
     * Note: Outer check for 'initialized' is a performance win since it
     * avoids an extra mutex lock in the common case.
     */

    if (!timeInfo.initialized) {
	TclpInitLock();
	if (!timeInfo.initialized) {
	    timeInfo.perfCounterAvailable =
		    QueryPerformanceFrequency(&timeInfo.nominalFreq);

	    /*
	     * Some hardware abstraction layers use the CPU clock in place of
	     * the real-time clock as a performance counter reference. This
	     * results in:
	     *    - inconsistent results among the processors on
	     *      multi-processor systems.
	     *    - unpredictable changes in performance counter frequency on
	     *      "gearshift" processors such as Transmeta and SpeedStep.
	     *
	     * There seems to be no way to test whether the performance
	     * counter is reliable, but a useful heuristic is that if its
	     * frequency is 1.193182 MHz or 3.579545 MHz, it's derived from a
	     * colorburst crystal and is therefore the RTC rather than the
	     * TSC.
	     *
	     * A sloppier but serviceable heuristic is that the RTC crystal is
	     * normally less than 15 MHz while the TSC crystal is virtually
	     * assured to be greater than 100 MHz. Since Win98SE appears to
	     * fiddle with the definition of the perf counter frequency
	     * (perhaps in an attempt to calibrate the clock?), we use the
	     * latter rule rather than an exact match.
	     *
	     * We also assume (perhaps questionably) that the vendors have
	     * gotten their act together on Win64, so bypass all this rubbish
	     * on that platform.
	     */

#if !defined(_WIN64)
	    if (timeInfo.perfCounterAvailable
		    /*
		     * The following lines would do an exact match on crystal
		     * frequency:
		     * && timeInfo.nominalFreq.QuadPart != (Tcl_WideInt)1193182
		     * && timeInfo.nominalFreq.QuadPart != (Tcl_WideInt)3579545
		     */
		    && timeInfo.nominalFreq.QuadPart > (Tcl_WideInt) 15000000){
		/*
		 * As an exception, if every logical processor on the system
		 * is on the same chip, we use the performance counter anyway,
		 * presuming that everyone's TSC is locked to the same
		 * oscillator.
		 */

		SYSTEM_INFO systemInfo;
		int regs[4];

		GetSystemInfo(&systemInfo);
		if (TclWinCPUID(0, regs) == TCL_OK
			&& regs[1] == 0x756e6547	/* "Genu" */
			&& regs[3] == 0x49656e69	/* "ineI" */
			&& regs[2] == 0x6c65746e	/* "ntel" */
			&& TclWinCPUID(1, regs) == TCL_OK
			&& ((regs[0]&0x00000F00) == 0x00000F00 /* Pentium 4 */
			|| ((regs[0] & 0x00F00000)	/* Extended family */
			&& (regs[3] & 0x10000000)))	/* Hyperthread */
			&& (((regs[1]&0x00FF0000) >> 16)/* CPU count */
			    == (int)systemInfo.dwNumberOfProcessors)) {
		    timeInfo.perfCounterAvailable = TRUE;
		} else {
		    timeInfo.perfCounterAvailable = FALSE;
		}
	    }
#endif /* above code is Win32 only */

	    /*
	     * If the performance counter is available, start a thread to
	     * calibrate it.
	     */

	    if (timeInfo.perfCounterAvailable) {
		DWORD id;

		InitializeCriticalSection(&timeInfo.cs);
		timeInfo.readyEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
		timeInfo.exitEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
		timeInfo.calibrationThread = CreateThread(NULL, 256,
			CalibrationThread, (LPVOID) NULL, 0, &id);
		SetThreadPriority(timeInfo.calibrationThread,
			THREAD_PRIORITY_HIGHEST);

		/*
		 * Wait for the thread just launched to start running, and
		 * create an exit handler that kills it so that it doesn't
		 * outlive unloading tclXX.dll
		 */

		WaitForSingleObject(timeInfo.readyEvent, INFINITE);
		CloseHandle(timeInfo.readyEvent);
		Tcl_CreateExitHandler(StopCalibration, NULL);
	    }
	    timeInfo.initialized = TRUE;
	}
	TclpInitUnlock();
    }

    if (timeInfo.perfCounterAvailable && timeInfo.curCounterFreq.QuadPart!=0) {
	/*
	 * Query the performance counter and use it to calculate the current
	 * time.
	 */

	ULARGE_INTEGER fileTimeLastCall;
	LARGE_INTEGER perfCounterLastCall, curCounterFreq;
				/* Copy with current data of calibration cycle */

	LARGE_INTEGER curCounter;
				/* Current performance counter. */
	Tcl_WideInt curFileTime;/* Current estimated time, expressed as 100-ns
				 * ticks since the Windows epoch. */
	static LARGE_INTEGER posixEpoch;
				/* Posix epoch expressed as 100-ns ticks since
				 * the windows epoch. */
	Tcl_WideInt usecSincePosixEpoch;
				/* Current microseconds since Posix epoch. */

	posixEpoch.LowPart = 0xD53E8000;
	posixEpoch.HighPart = 0x019DB1DE;

	QueryPerformanceCounter(&curCounter);

	/*
	 * Hold time section locked as short as possible
	 */
	EnterCriticalSection(&timeInfo.cs);

	fileTimeLastCall.QuadPart = timeInfo.fileTimeLastCall.QuadPart;
	perfCounterLastCall.QuadPart = timeInfo.perfCounterLastCall.QuadPart;
	curCounterFreq.QuadPart = timeInfo.curCounterFreq.QuadPart;

	LeaveCriticalSection(&timeInfo.cs);

	/*
	 * If calibration cycle occurred after we get curCounter
	 */
	if (curCounter.QuadPart <= perfCounterLastCall.QuadPart) {
	    usecSincePosixEpoch =
		(fileTimeLastCall.QuadPart - posixEpoch.QuadPart) / 10;
	    return usecSincePosixEpoch;
	}

	/*
	 * If it appears to be more than 1.1 seconds since the last trip
	 * through the calibration loop, the performance counter may have
	 * jumped forward. (See MSDN Knowledge Base article Q274323 for a
	 * description of the hardware problem that makes this test
	 * necessary.) If the counter jumps, we don't want to use it directly.
	 * Instead, we must return system time. Eventually, the calibration
	 * loop should recover.
	 */

	if (curCounter.QuadPart - perfCounterLastCall.QuadPart <
		11 * curCounterFreq.QuadPart / 10
	) {
	    curFileTime = fileTimeLastCall.QuadPart +
		 ((curCounter.QuadPart - perfCounterLastCall.QuadPart)
		    * 10000000 / curCounterFreq.QuadPart);

	    usecSincePosixEpoch = (curFileTime - posixEpoch.QuadPart) / 10;
	    return usecSincePosixEpoch;
	}
    }

    /*
     * High resolution timer is not available.
     */
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * NativeGetTime --
 *
 *	TIP #233: Gets the current system time in seconds and microseconds
 *	since the beginning of the epoch: 00:00 UCT, January 1, 1970.
 *
 * Results:
 *	Returns the current time in timePtr.
 *
 * Side effects:
 *	See NativeGetMicroseconds for more information.
 *
 *----------------------------------------------------------------------
 */

static void
NativeGetTime(
    Tcl_Time *timePtr,
    ClientData clientData)
{
    Tcl_WideInt usecSincePosixEpoch;

    /*
     * Try to use high resolution timer.
     */
    if ( (usecSincePosixEpoch = NativeGetMicroseconds()) ) {
	timePtr->sec = (long) (usecSincePosixEpoch / 1000000);
	timePtr->usec = (unsigned long) (usecSincePosixEpoch % 1000000);
    } else {
	/*
	* High resolution timer is not available. Just use ftime.
	*/

	struct _timeb t;

	_ftime(&t);
	timePtr->sec = (long)t.time;
	timePtr->usec = t.millitm * 1000;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * StopCalibration --
 *
 *	Turns off the calibration thread in preparation for exiting the
 *	process.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Sets the 'exitEvent' event in the 'timeInfo' structure to ask the
 *	thread in question to exit, and waits for it to do so.
 *
 *----------------------------------------------------------------------
 */

static void
StopCalibration(
    ClientData unused)		/* Client data is unused */
{
    SetEvent(timeInfo.exitEvent);

    /*
     * If Tcl_Finalize was called from DllMain, the calibration thread is in a
     * paused state so we need to timeout and continue.
     */

    WaitForSingleObject(timeInfo.calibrationThread, 100);
    CloseHandle(timeInfo.exitEvent);
    CloseHandle(timeInfo.calibrationThread);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpGetDate --
 *
 *	This function converts between seconds and struct tm. If useGMT is
 *	true, then the returned date will be in Greenwich Mean Time (GMT).
 *	Otherwise, it will be in the local time zone.
 *
 * Results:
 *	Returns a static tm structure.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

struct tm *
TclpGetDate(
    const time_t *t,
    int useGMT)
{
    struct tm *tmPtr;
    time_t time;

    if (!useGMT) {
	tzset();

	/*
	 * If we are in the valid range, let the C run-time library handle it.
	 * Otherwise we need to fake it. Note that this algorithm ignores
	 * daylight savings time before the epoch.
	 */

	/*
	 * Hm, Borland's localtime manages to return NULL under certain
	 * circumstances (e.g. wintime.test, test 1.2). Nobody tests for this,
	 * since 'localtime' isn't supposed to do this, possibly leading to
	 * crashes.
	 *
	 * Patch: We only call this function if we are at least one day into
	 * the epoch, else we handle it ourselves (like we do for times < 0).
	 * H. Giese, June 2003
	 */

#ifdef __BORLANDC__
#define LOCALTIME_VALIDITY_BOUNDARY	SECSPERDAY
#else
#define LOCALTIME_VALIDITY_BOUNDARY	0
#endif

	if (*t >= LOCALTIME_VALIDITY_BOUNDARY) {
	    return TclpLocaltime(t);
	}

	time = *t - timezone;

	/*
	 * If we aren't near to overflowing the long, just add the bias and
	 * use the normal calculation. Otherwise we will need to adjust the
	 * result at the end.
	 */

	if (*t < (LONG_MAX - 2*SECSPERDAY) && *t > (LONG_MIN + 2*SECSPERDAY)) {
	    tmPtr = ComputeGMT(&time);
	} else {
	    tmPtr = ComputeGMT(t);

	    tzset();

	    /*
	     * Add the bias directly to the tm structure to avoid overflow.
	     * Propagate seconds overflow into minutes, hours and days.
	     */

	    time = tmPtr->tm_sec - timezone;
	    tmPtr->tm_sec = (int)(time % 60);
	    if (tmPtr->tm_sec < 0) {
		tmPtr->tm_sec += 60;
		time -= 60;
	    }

	    time = tmPtr->tm_min + time/60;
	    tmPtr->tm_min = (int)(time % 60);
	    if (tmPtr->tm_min < 0) {
		tmPtr->tm_min += 60;
		time -= 60;
	    }

	    time = tmPtr->tm_hour + time/60;
	    tmPtr->tm_hour = (int)(time % 24);
	    if (tmPtr->tm_hour < 0) {
		tmPtr->tm_hour += 24;
		time -= 24;
	    }

	    time /= 24;
	    tmPtr->tm_mday += (int)time;
	    tmPtr->tm_yday += (int)time;
	    tmPtr->tm_wday = (tmPtr->tm_wday + (int)time) % 7;
	}
    } else {
	tmPtr = ComputeGMT(t);
    }
    return tmPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * ComputeGMT --
 *
 *	This function computes GMT given the number of seconds since the epoch
 *	(midnight Jan 1 1970).
 *
 * Results:
 *	Returns a (per thread) statically allocated struct tm.
 *
 * Side effects:
 *	Updates the values of the static struct tm.
 *
 *----------------------------------------------------------------------
 */

static struct tm *
ComputeGMT(
    const time_t *tp)
{
    struct tm *tmPtr;
    long tmp, rem;
    int isLeap;
    const int *days;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    tmPtr = &tsdPtr->tm;

    /*
     * Compute the 4 year span containing the specified time.
     */

    tmp = (long)(*tp / SECSPER4YEAR);
    rem = (long)(*tp % SECSPER4YEAR);

    /*
     * Correct for weird mod semantics so the remainder is always positive.
     */

    if (rem < 0) {
	tmp--;
	rem += SECSPER4YEAR;
    }

    /*
     * Compute the year after 1900 by taking the 4 year span and adjusting for
     * the remainder. This works because 2000 is a leap year, and 1900/2100
     * are out of the range.
     */

    tmp = (tmp * 4) + 70;
    isLeap = 0;
    if (rem >= SECSPERYEAR) {			  /* 1971, etc. */
	tmp++;
	rem -= SECSPERYEAR;
	if (rem >= SECSPERYEAR) {		  /* 1972, etc. */
	    tmp++;
	    rem -= SECSPERYEAR;
	    if (rem >= SECSPERYEAR + SECSPERDAY) { /* 1973, etc. */
		tmp++;
		rem -= SECSPERYEAR + SECSPERDAY;
	    } else {
		isLeap = 1;
	    }
	}
    }
    tmPtr->tm_year = tmp;

    /*
     * Compute the day of year and leave the seconds in the current day in the
     * remainder.
     */

    tmPtr->tm_yday = rem / SECSPERDAY;
    rem %= SECSPERDAY;

    /*
     * Compute the time of day.
     */

    tmPtr->tm_hour = rem / 3600;
    rem %= 3600;
    tmPtr->tm_min = rem / 60;
    tmPtr->tm_sec = rem % 60;

    /*
     * Compute the month and day of month.
     */

    days = (isLeap) ? leapDays : normalDays;
    for (tmp = 1; days[tmp] < tmPtr->tm_yday; tmp++) {
	/* empty body */
    }
    tmPtr->tm_mon = --tmp;
    tmPtr->tm_mday = tmPtr->tm_yday - days[tmp];

    /*
     * Compute day of week.  Epoch started on a Thursday.
     */

    tmPtr->tm_wday = (long)(*tp / SECSPERDAY) + 4;
    if ((*tp % SECSPERDAY) < 0) {
	tmPtr->tm_wday--;
    }
    tmPtr->tm_wday %= 7;
    if (tmPtr->tm_wday < 0) {
	tmPtr->tm_wday += 7;
    }

    return tmPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * CalibrationThread --
 *
 *	Thread that manages calibration of the hi-resolution time derived from
 *	the performance counter, to keep it synchronized with the system
 *	clock.
 *
 * Parameters:
 *	arg - Client data from the CreateThread call. This parameter points to
 *	      the static TimeInfo structure.
 *
 * Return value:
 *	None. This thread embeds an infinite loop.
 *
 * Side effects:
 *	At an interval of 1s, this thread performs virtual time discipline.
 *
 * Note: When this thread is entered, TclpInitLock has been called to
 * safeguard the static storage. There is therefore no synchronization in the
 * body of this procedure.
 *
 *----------------------------------------------------------------------
 */

static DWORD WINAPI
CalibrationThread(
    LPVOID arg)
{
    FILETIME curFileTime;
    DWORD waitResult;

    /*
     * Get initial system time and performance counter.
     */

    GetSystemTimeAsFileTime(&curFileTime);
    QueryPerformanceCounter(&timeInfo.perfCounterLastCall);
    QueryPerformanceFrequency(&timeInfo.curCounterFreq);
    timeInfo.fileTimeLastCall.LowPart = curFileTime.dwLowDateTime;
    timeInfo.fileTimeLastCall.HighPart = curFileTime.dwHighDateTime;

    ResetCounterSamples(timeInfo.fileTimeLastCall.QuadPart,
	    timeInfo.perfCounterLastCall.QuadPart,
	    timeInfo.curCounterFreq.QuadPart);

    /*
     * Wake up the calling thread. When it wakes up, it will release the
     * initialization lock.
     */

    SetEvent(timeInfo.readyEvent);

    /*
     * Run the calibration once a second.
     */

    while (timeInfo.perfCounterAvailable) {
	/*
	 * If the exitEvent is set, break out of the loop.
	 */

	waitResult = WaitForSingleObjectEx(timeInfo.exitEvent, 1000, FALSE);
	if (waitResult == WAIT_OBJECT_0) {
	    break;
	}
	UpdateTimeEachSecond();
    }

    /* lint */
    return (DWORD) 0;
}

/*
 *----------------------------------------------------------------------
 *
 * UpdateTimeEachSecond --
 *
 *	Callback from the waitable timer in the clock calibration thread that
 *	updates system time.
 *
 * Parameters:
 *	info - Pointer to the static TimeInfo structure
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Performs virtual time calibration discipline.
 *
 *----------------------------------------------------------------------
 */

static void
UpdateTimeEachSecond(void)
{
    LARGE_INTEGER curPerfCounter;
				/* Current value returned from
				 * QueryPerformanceCounter. */
    FILETIME curSysTime;	/* Current system time. */
    LARGE_INTEGER curFileTime;	/* File time at the time this callback was
				 * scheduled. */
    Tcl_WideInt estFreq;	/* Estimated perf counter frequency. */
    Tcl_WideInt vt0;		/* Tcl time right now. */
    Tcl_WideInt vt1;		/* Tcl time one second from now. */
    Tcl_WideInt tdiff;		/* Difference between system clock and Tcl
				 * time. */
    Tcl_WideInt driftFreq;	/* Frequency needed to drift virtual time into
				 * step over 1 second. */

    /*
     * Sample performance counter and system time.
     */

    QueryPerformanceCounter(&curPerfCounter);
    GetSystemTimeAsFileTime(&curSysTime);
    curFileTime.LowPart = curSysTime.dwLowDateTime;
    curFileTime.HighPart = curSysTime.dwHighDateTime;

    EnterCriticalSection(&timeInfo.cs);

    /*
     * We devide by timeInfo.curCounterFreq.QuadPart in several places. That
     * value should always be positive on a correctly functioning system. But
     * it is good to be defensive about such matters. So if something goes
     * wrong and the value does goes to zero, we clear the
     * timeInfo.perfCounterAvailable in order to cause the calibration thread
     * to shut itself down, then return without additional processing.
     */

    if (timeInfo.curCounterFreq.QuadPart == 0){
	LeaveCriticalSection(&timeInfo.cs);
	timeInfo.perfCounterAvailable = 0;
	return;
    }

    /*
     * Several things may have gone wrong here that have to be checked for.
     *  (1) The performance counter may have jumped.
     *  (2) The system clock may have been reset.
     *
     * In either case, we'll need to reinitialize the circular buffer with
     * samples relative to the current system time and the NOMINAL performance
     * frequency (not the actual, because the actual has probably run slow in
     * the first case). Our estimated frequency will be the nominal frequency.
     *
     * Store the current sample into the circular buffer of samples, and
     * estimate the performance counter frequency.
     */

    estFreq = AccumulateSample(curPerfCounter.QuadPart,
	    (Tcl_WideUInt) curFileTime.QuadPart);

    /*
     * We want to adjust things so that time appears to be continuous.
     * Virtual file time, right now, is
     *
     * vt0 = 10000000 * (curPerfCounter - perfCounterLastCall)
     *	     / curCounterFreq
     *	     + fileTimeLastCall
     *
     * Ideally, we would like to drift the clock into place over a period of 2
     * sec, so that virtual time 2 sec from now will be
     *
     * vt1 = 20000000 + curFileTime
     *
     * The frequency that we need to use to drift the counter back into place
     * is estFreq * 20000000 / (vt1 - vt0)
     */

    vt0 = 10000000 * (curPerfCounter.QuadPart
		- timeInfo.perfCounterLastCall.QuadPart)
	    / timeInfo.curCounterFreq.QuadPart
	    + timeInfo.fileTimeLastCall.QuadPart;
    vt1 = 20000000 + curFileTime.QuadPart;

    /*
     * If we've gotten more than a second away from system time, then drifting
     * the clock is going to be pretty hopeless. Just let it jump. Otherwise,
     * compute the drift frequency and fill in everything.
     */

    tdiff = vt0 - curFileTime.QuadPart;
    if (tdiff > 10000000 || tdiff < -10000000) {
	timeInfo.fileTimeLastCall.QuadPart = curFileTime.QuadPart;
	timeInfo.curCounterFreq.QuadPart = estFreq;
    } else {
	driftFreq = estFreq * 20000000 / (vt1 - vt0);

	if (driftFreq > 1003*estFreq/1000) {
	    driftFreq = 1003*estFreq/1000;
	} else if (driftFreq < 997*estFreq/1000) {
	    driftFreq = 997*estFreq/1000;
	}

	timeInfo.fileTimeLastCall.QuadPart = vt0;
	timeInfo.curCounterFreq.QuadPart = driftFreq;
    }

    timeInfo.perfCounterLastCall.QuadPart = curPerfCounter.QuadPart;

    LeaveCriticalSection(&timeInfo.cs);
}

/*
 *----------------------------------------------------------------------
 *
 * ResetCounterSamples --
 *
 *	Fills the sample arrays in 'timeInfo' with dummy values that will
 *	yield the current performance counter and frequency.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The array of samples is filled in so that it appears that there are
 *	SAMPLES samples at one-second intervals, separated by precisely the
 *	given frequency.
 *
 *----------------------------------------------------------------------
 */

static void
ResetCounterSamples(
    Tcl_WideUInt fileTime,	/* Current file time */
    Tcl_WideInt perfCounter,	/* Current performance counter */
    Tcl_WideInt perfFreq)	/* Target performance frequency */
{
    int i;
    for (i=SAMPLES-1 ; i>=0 ; --i) {
	timeInfo.perfCounterSample[i] = perfCounter;
	timeInfo.fileTimeSample[i] = fileTime;
	perfCounter -= perfFreq;
	fileTime -= 10000000;
    }
    timeInfo.sampleNo = 0;
}

/*
 *----------------------------------------------------------------------
 *
 * AccumulateSample --
 *
 *	Updates the circular buffer of performance counter and system time
 *	samples with a new data point.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The new data point replaces the oldest point in the circular buffer,
 *	and the descriptive statistics are updated to accumulate the new
 *	point.
 *
 * Several things may have gone wrong here that have to be checked for.
 *  (1) The performance counter may have jumped.
 *  (2) The system clock may have been reset.
 *
 * In either case, we'll need to reinitialize the circular buffer with samples
 * relative to the current system time and the NOMINAL performance frequency
 * (not the actual, because the actual has probably run slow in the first
 * case).
 */

static Tcl_WideInt
AccumulateSample(
    Tcl_WideInt perfCounter,
    Tcl_WideUInt fileTime)
{
    Tcl_WideUInt workFTSample;	/* File time sample being removed from or
				 * added to the circular buffer. */
    Tcl_WideInt workPCSample;	/* Performance counter sample being removed
				 * from or added to the circular buffer. */
    Tcl_WideUInt lastFTSample;	/* Last file time sample recorded */
    Tcl_WideInt lastPCSample;	/* Last performance counter sample recorded */
    Tcl_WideInt FTdiff;		/* Difference between last FT and current */
    Tcl_WideInt PCdiff;		/* Difference between last PC and current */
    Tcl_WideInt estFreq;	/* Estimated performance counter frequency */

    /*
     * Test for jumps and reset the samples if we have one.
     */

    if (timeInfo.sampleNo == 0) {
	lastPCSample =
		timeInfo.perfCounterSample[timeInfo.sampleNo + SAMPLES - 1];
	lastFTSample =
		timeInfo.fileTimeSample[timeInfo.sampleNo + SAMPLES - 1];
    } else {
	lastPCSample = timeInfo.perfCounterSample[timeInfo.sampleNo - 1];
	lastFTSample = timeInfo.fileTimeSample[timeInfo.sampleNo - 1];
    }

    PCdiff = perfCounter - lastPCSample;
    FTdiff = fileTime - lastFTSample;
    if (PCdiff < timeInfo.nominalFreq.QuadPart * 9 / 10
	    || PCdiff > timeInfo.nominalFreq.QuadPart * 11 / 10
	    || FTdiff < 9000000 || FTdiff > 11000000) {
	ResetCounterSamples(fileTime, perfCounter,
		timeInfo.nominalFreq.QuadPart);
	return timeInfo.nominalFreq.QuadPart;
    } else {
	/*
	 * Estimate the frequency.
	 */

	workPCSample = timeInfo.perfCounterSample[timeInfo.sampleNo];
	workFTSample = timeInfo.fileTimeSample[timeInfo.sampleNo];
	estFreq = 10000000 * (perfCounter - workPCSample)
		/ (fileTime - workFTSample);
	timeInfo.perfCounterSample[timeInfo.sampleNo] = perfCounter;
	timeInfo.fileTimeSample[timeInfo.sampleNo] = (Tcl_WideInt) fileTime;

	/*
	 * Advance the sample number.
	 */

	if (++timeInfo.sampleNo >= SAMPLES) {
	    timeInfo.sampleNo = 0;
	}

	return estFreq;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TclpGmtime --
 *
 *	Wrapper around the 'gmtime' library function to make it thread safe.
 *
 * Results:
 *	Returns a pointer to a 'struct tm' in thread-specific data.
 *
 * Side effects:
 *	Invokes gmtime or gmtime_r as appropriate.
 *
 *----------------------------------------------------------------------
 */

struct tm *
TclpGmtime(
    const time_t *timePtr)	/* Pointer to the number of seconds since the
				 * local system's epoch */
{
    /*
     * The MS implementation of gmtime is thread safe because it returns the
     * time in a block of thread-local storage, and Windows does not provide a
     * Posix gmtime_r function.
     */

    return gmtime(timePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpLocaltime --
 *
 *	Wrapper around the 'localtime' library function to make it thread
 *	safe.
 *
 * Results:
 *	Returns a pointer to a 'struct tm' in thread-specific data.
 *
 * Side effects:
 *	Invokes localtime or localtime_r as appropriate.
 *
 *----------------------------------------------------------------------
 */

struct tm *
TclpLocaltime(
    const time_t *timePtr)	/* Pointer to the number of seconds since the
				 * local system's epoch */
{
    /*
     * The MS implementation of localtime is thread safe because it returns
     * the time in a block of thread-local storage, and Windows does not
     * provide a Posix localtime_r function.
     */

    return localtime(timePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_SetTimeProc --
 *
 *	TIP #233 (Virtualized Time): Registers two handlers for the
 *	virtualization of Tcl's access to time information.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Remembers the handlers, alters core behaviour.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_SetTimeProc(
    Tcl_GetTimeProc *getProc,
    Tcl_ScaleTimeProc *scaleProc,
    ClientData clientData)
{
    tclGetTimeProcPtr = getProc;
    tclScaleTimeProcPtr = scaleProc;
    tclTimeClientData = clientData;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_QueryTimeProc --
 *
 *	TIP #233 (Virtualized Time): Query which time handlers are registered.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_QueryTimeProc(
    Tcl_GetTimeProc **getProc,
    Tcl_ScaleTimeProc **scaleProc,
    ClientData *clientData)
{
    if (getProc) {
	*getProc = tclGetTimeProcPtr;
    }
    if (scaleProc) {
	*scaleProc = tclScaleTimeProcPtr;
    }
    if (clientData) {
	*clientData = tclTimeClientData;
    }
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */