merge 8-5-timerate (?max-count?, break possibility, diverse fixes) + windows time-calibration cycle optimization [f6637d3dd8] (clock ticks never backwards, more precise and smooth drifting)

5 files changed, 230 insertions, 69 deletions

diff --git a/doc/timerate.n b/doc/timerate.n
index df9a8f7..2380597 100644
--- a/doc/timerate.n
+++ b/doc/timerate.n
@@ -11,17 +11,20 @@
 .SH NAME
 timerate \- Time-related execution resp. performance measurement of a script
 .SH SYNOPSIS
-\fBtimerate \fIscript\fR \fI?time?\fR
+\fBtimerate \fIscript\fR \fI?time ?max-count??\fR
 .sp
-\fBtimerate \fI?-direct?\fR \fI?-overhead double?\fR \fIscript\fR \fI?time?\fR
+\fBtimerate \fI?-direct?\fR \fI?-overhead double?\fR \fIscript\fR \fI?time ?max-count??\fR
 .sp
-\fBtimerate \fI?-calibrate?\fR \fI?-direct?\fR \fIscript\fR \fI?time?\fR
+\fBtimerate \fI?-calibrate?\fR \fI?-direct?\fR \fIscript\fR \fI?time ?max-count??\fR
 .BE
 .SH DESCRIPTION
 .PP
 The first and second form will evaluate \fIscript\fR until the interval
 \fItime\fR given in milliseconds elapses, or for 1000 milliseconds (1 second)
-if \fItime\fR is not specified. 
+if \fItime\fR is not specified.
+.sp
+If \fImax-count\fR is specified, it imposes a further restriction by the maximal 
+number of iterations.
 .sp
 It will then return a canonical tcl-list of the form
 .PP
diff --git a/generic/tclCmdMZ.c b/generic/tclCmdMZ.c
index dd4c2a6..4bc82e4 100644
--- a/generic/tclCmdMZ.c
+++ b/generic/tclCmdMZ.c
@@ -4299,8 +4299,10 @@ Tcl_TimeRateObjCmd(
     register int result, i;
     Tcl_Obj *calibrate = NULL, *direct = NULL;
     Tcl_WideUInt count = 0;	/* Holds repetition count */
-    Tcl_WideInt maxms = -0x7FFFFFFFFFFFFFFFL; 
+    Tcl_WideInt  maxms  = WIDE_MIN;
 				/* Maximal running time (in milliseconds) */
+    Tcl_WideUInt maxcnt = WIDE_MAX;
+				/* Maximal count of iterations. */
     Tcl_WideUInt threshold = 1;	/* Current threshold for check time (faster
 				 * repeat count without time check) */
     Tcl_WideUInt maxIterTm = 1;	/* Max time of some iteration as max threshold
@@ -4350,24 +4352,32 @@ Tcl_TimeRateObjCmd(
 	}
     }
 
-    if (i >= objc || i < objc-2) {
+    if (i >= objc || i < objc-3) {
 usage:
-	Tcl_WrongNumArgs(interp, 1, objv, "?-direct? ?-calibrate? ?-overhead double? command ?time?");
+	Tcl_WrongNumArgs(interp, 1, objv, "?-direct? ?-calibrate? ?-overhead double? command ?time ?max-count??");
 	return TCL_ERROR;
     }
     objPtr = objv[i++];
-    if (i < objc) {
-	result = TclGetWideIntFromObj(interp, objv[i], &maxms);
+    if (i < objc) {	/* max-time */
+	result = Tcl_GetWideIntFromObj(interp, objv[i++], &maxms);
 	if (result != TCL_OK) {
 	    return result;
 	}
+	if (i < objc) {	/* max-count*/
+	    Tcl_WideInt v;
+	    result = Tcl_GetWideIntFromObj(interp, objv[i], &v);
+	    if (result != TCL_OK) {
+		return result;
+	    }
+	    maxcnt = (v > 0) ? v : 0;
+	}
     }
 
     /* if calibrate */
     if (calibrate) {
 
 	/* if no time specified for the calibration */
-	if (maxms == -0x7FFFFFFFFFFFFFFFL) {
+	if (maxms == WIDE_MIN) {
 	    Tcl_Obj *clobjv[6];
 	    Tcl_WideInt maxCalTime = 5000;
 	    double lastMeasureOverhead = measureOverhead;
@@ -4397,7 +4407,7 @@ usage:
 	    clobjv[i++] = objPtr; 
 
 	    /* set last measurement overhead to max */
-	    measureOverhead = (double)0x7FFFFFFFFFFFFFFFL;
+	    measureOverhead = (double)UWIDE_MAX;
 
 	    /* calibration cycle until it'll be preciser */
 	    maxms = -1000;
@@ -4431,14 +4441,14 @@ usage:
 	/* if time is negative - make current overhead more precise */
 	if (maxms > 0) {
 	    /* set last measurement overhead to max */
-	    measureOverhead = (double)0x7FFFFFFFFFFFFFFFL;
+	    measureOverhead = (double)UWIDE_MAX;
 	} else {
 	    maxms = -maxms;
 	}
 
     }
 
-    if (maxms == -0x7FFFFFFFFFFFFFFFL) {
+    if (maxms == WIDE_MIN) {
     	maxms = 1000;
     }
     if (overhead == -1) {
@@ -4471,6 +4481,7 @@ usage:
 #endif
 
     /* start measurement */
+    if (maxcnt > 0)
     while (1) {
     	/* eval single iteration */
     	count++;
@@ -4485,7 +4496,14 @@ usage:
 	    result = TclEvalObjEx(interp, objPtr, 0, NULL, 0);
 	}
 	if (result != TCL_OK) {
-	    goto done;
+	    /* allow break from measurement cycle (used for conditional stop) */
+	    if (result != TCL_BREAK) {
+		goto done;
+	    }
+	    /* force stop immediately */
+	    threshold = 1;
+	    maxcnt = 0;
+	    result = TCL_OK;
 	}
 	
 	/* don't check time up to threshold */
@@ -4498,7 +4516,7 @@ usage:
 	Tcl_GetTime(&now);
 	middle = now.sec; middle *= 1000000; middle += now.usec;
     #endif
-	if (middle >= stop) {
+	if (middle >= stop || count >= maxcnt) {
 	    break;
 	}
 
@@ -4533,6 +4551,10 @@ usage:
 	if (threshold > 100000) {	    /* fix for too large threshold */
 	    threshold = 100000;
 	}
+	/* consider max-count */
+	if (threshold > maxcnt - count) {
+	    threshold = maxcnt - count;
+	}
     }
 
     {
@@ -4552,11 +4574,11 @@ usage:
 	    /* minimize influence of measurement overhead */
 	    if (overhead > 0) {
 		/* estimate the time of overhead (microsecs) */
-		Tcl_WideInt curOverhead = overhead * count;
+		Tcl_WideUInt curOverhead = overhead * count;
 		if (middle > curOverhead) {
 		    middle -= curOverhead;
 		} else {
-		    middle = 1;
+		    middle = 0;
 		}
 	    }
 	} else {
@@ -4585,7 +4607,7 @@ usage:
 	
 	/* calculate speed as rate (count) per sec */
 	if (!middle) middle++; /* +1 ms, just to avoid divide by zero */
-	if (count < (0x7FFFFFFFFFFFFFFFL / 1000000)) {
+	if (count < (WIDE_MAX / 1000000)) {
 	    val = (count * 1000000) / middle;
 	    if (val < 100000) {
 		if (val < 100)	{ fmt = "%.3f"; } else
diff --git a/generic/tclPort.h b/generic/tclPort.h
index 12a60db..9485567 100644
--- a/generic/tclPort.h
+++ b/generic/tclPort.h
@@ -39,5 +39,8 @@
 #   define LLONG_MAX (~LLONG_MIN)
 #endif
 
+#define UWIDE_MAX ((Tcl_WideUInt)-1)
+#define WIDE_MAX ((Tcl_WideInt)(UWIDE_MAX >> 1))
+#define WIDE_MIN ((Tcl_WideInt)((Tcl_WideUInt)WIDE_MAX+1))
 
 #endif /* _TCLPORT */
diff --git a/tests/cmdMZ.test b/tests/cmdMZ.test
index 2d68138..c3afc8d 100644
--- a/tests/cmdMZ.test
+++ b/tests/cmdMZ.test
@@ -342,6 +342,70 @@ test cmdMZ-5.7 {Tcl_TimeObjCmd: errors generate right trace} {
     invoked from within
 "time {error foo}"}}
 
+test cmdMZ-6.1 {Tcl_TimeRateObjCmd: basic format of command} {
+    list [catch {timerate} msg] $msg
+} {1 {wrong # args: should be "timerate ?-direct? ?-calibrate? ?-overhead double? command ?time ?max-count??"}}
+test cmdMZ-6.2.1 {Tcl_TimeRateObjCmd: basic format of command} {
+    list [catch {timerate a b c d} msg] $msg
+} {1 {wrong # args: should be "timerate ?-direct? ?-calibrate? ?-overhead double? command ?time ?max-count??"}}
+test cmdMZ-6.2.2 {Tcl_TimeRateObjCmd: basic format of command} {
+    list [catch {timerate a b c} msg] $msg
+} {1 {expected integer but got "b"}}
+test cmdMZ-6.2.3 {Tcl_TimeRateObjCmd: basic format of command} {
+    list [catch {timerate a b} msg] $msg
+} {1 {expected integer but got "b"}}
+test cmdMZ-6.3 {Tcl_TimeRateObjCmd: basic format of command} {
+    list [catch {timerate -overhead b {} a b} msg] $msg
+} {1 {expected floating-point number but got "b"}}
+test cmdMZ-6.4 {Tcl_TimeRateObjCmd: compile of script happens even with negative iteration counts} {
+    list [catch {timerate "foreach a {c d e} \{" -12456} msg] $msg
+} {1 {missing close-brace}}
+test cmdMZ-6.5 {Tcl_TimeRateObjCmd: result format and one iteration} {
+    regexp {^\d+.\d+ \ws/# 1 # \d+ #/sec \d+.\d+ nett-ms$} [timerate {} 0]
+} 1
+test cmdMZ-6.6 {Tcl_TimeRateObjCmd: slower commands take longer, but it remains almost the same time of measument} {
+    set m1 [timerate {after 0} 20]
+    set m2 [timerate {after 1} 20]
+    list \
+	[expr {[lindex $m1 0] < [lindex $m2 0]}] \
+	[expr {[lindex $m1 0] < 100}] \
+	[expr {[lindex $m2 0] >= 500}] \
+	[expr {[lindex $m1 2] > 1000}] \
+	[expr {[lindex $m2 2] <= 50}] \
+	[expr {[lindex $m1 4] > 10000}] \
+	[expr {[lindex $m2 4] < 10000}] \
+	[expr {[lindex $m1 6] > 10 && [lindex $m1 6] < 50}] \
+	[expr {[lindex $m2 6] > 10 && [lindex $m2 6] < 50}]
+} [lrepeat 9 1]
+test cmdMZ-6.7 {Tcl_TimeRateObjCmd: errors generate right trace} {
+    list [catch {timerate {error foo} 1} msg] $msg $::errorInfo
+} {1 foo {foo
+    while executing
+"error foo"
+    invoked from within
+"timerate {error foo} 1"}}
+test cmdMZ-6.8 {Tcl_TimeRateObjCmd: allow (conditional) break from timerate} {
+    set m1 [timerate {break}]
+    list \
+	[expr {[lindex $m1 0] < 1000}] \
+	[expr {[lindex $m1 2] == 1}] \
+	[expr {[lindex $m1 4] > 1000}] \
+	[expr {[lindex $m1 6] < 10}]
+} {1 1 1 1}
+test cmdMZ-6.9 {Tcl_TimeRateObjCmd: max count of iterations} {
+    set m1 [timerate {} 1000 5];	# max-count wins
+    set m2 [timerate {after 20} 1 5];	# max-time wins
+    list [lindex $m1 2] [lindex $m2 2]
+} {5 1}
+test cmdMZ-6.10 {Tcl_TimeRateObjCmd: huge overhead cause 0us result} {
+    set m1 [timerate -overhead 1e6 {after 10} 100 1]
+    list \
+	[expr {[lindex $m1 0] == 0.0}] \
+	[expr {[lindex $m1 2] == 1}] \
+	[expr {[lindex $m1 4] == 1000000}] \
+	[expr {[lindex $m1 6] <= 0.001}]
+} {1 1 1 1}
+
 # The tests for Tcl_WhileObjCmd are in while.test
 
 # cleanup
diff --git a/win/tclWinTime.c b/win/tclWinTime.c
index fd14595..d4e84ba 100644
--- a/win/tclWinTime.c
+++ b/win/tclWinTime.c
@@ -51,6 +51,7 @@ typedef struct TimeInfo {
 				 * initialized. */
     int perfCounterAvailable;	/* Flag == 1 if the hardware has a performance
 				 * counter. */
+    DWORD calibrationInterv;	/* Calibration interval in seconds (start 1 sec) */
     HANDLE calibrationThread;	/* Handle to the thread that keeps the virtual
 				 * clock calibrated. */
     HANDLE readyEvent;		/* System event used to trigger the requesting
@@ -61,7 +62,6 @@ typedef struct TimeInfo {
     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:
@@ -74,6 +74,8 @@ typedef struct TimeInfo {
     ULARGE_INTEGER fileTimeLastCall;
     LARGE_INTEGER perfCounterLastCall;
     LARGE_INTEGER curCounterFreq;
+    LARGE_INTEGER posixEpoch;	/* Posix epoch expressed as 100-ns ticks since
+				 * the windows epoch. */
 
     /*
      * Data used in developing the estimate of performance counter frequency
@@ -90,6 +92,7 @@ static TimeInfo timeInfo = {
     { NULL, 0, 0, NULL, NULL, 0 },
     0,
     0,
+    1,
     (HANDLE) NULL,
     (HANDLE) NULL,
     (HANDLE) NULL,
@@ -98,11 +101,13 @@ static TimeInfo timeInfo = {
     (ULARGE_INTEGER) (DWORDLONG) 0,
     (LARGE_INTEGER) (Tcl_WideInt) 0,
     (LARGE_INTEGER) (Tcl_WideInt) 0,
+    (LARGE_INTEGER) (Tcl_WideInt) 0,
 #else
-    0,
-    0,
-    0,
-    0,
+    {0, 0},
+    {0, 0},
+    {0, 0},
+    {0, 0},
+    {0, 0},
 #endif
     { 0 },
     { 0 },
@@ -435,12 +440,20 @@ NativeScaleTime(
  *----------------------------------------------------------------------
  */
 
+static inline Tcl_WideInt
+NativeCalc100NsTicks(
+    ULONGLONG fileTimeLastCall,
+    LONGLONG perfCounterLastCall,
+    LONGLONG curCounterFreq,
+    LONGLONG curCounter
+) {
+    return fileTimeLastCall + 
+	((curCounter - perfCounterLastCall) * 10000000 / curCounterFreq);
+}
+
 static Tcl_WideInt
 NativeGetMicroseconds(void)
 {
-    static LARGE_INTEGER posixEpoch;
-				/* Posix epoch expressed as 100-ns ticks since
-				 * the windows epoch. */
     /*
      * Initialize static storage on the first trip through.
      *
@@ -452,8 +465,8 @@ NativeGetMicroseconds(void)
 	TclpInitLock();
 	if (!timeInfo.initialized) {
 
-	    posixEpoch.LowPart = 0xD53E8000;
-	    posixEpoch.HighPart = 0x019DB1DE;
+	    timeInfo.posixEpoch.LowPart = 0xD53E8000;
+	    timeInfo.posixEpoch.HighPart = 0x019DB1DE;
 
 	    timeInfo.perfCounterAvailable =
 		    QueryPerformanceFrequency(&timeInfo.nominalFreq);
@@ -559,16 +572,12 @@ NativeGetMicroseconds(void)
 	 * time.
 	 */
 
-	ULARGE_INTEGER fileTimeLastCall;
-	LARGE_INTEGER perfCounterLastCall, curCounterFreq;
+	ULONGLONG fileTimeLastCall;
+	LONGLONG 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. */
-	Tcl_WideInt usecSincePosixEpoch;
-				/* Current microseconds since Posix epoch. */
 
 	QueryPerformanceCounter(&curCounter);
 
@@ -577,19 +586,18 @@ NativeGetMicroseconds(void)
 	 */
 	EnterCriticalSection(&timeInfo.cs);
 
-	fileTimeLastCall.QuadPart = timeInfo.fileTimeLastCall.QuadPart;
-	perfCounterLastCall.QuadPart = timeInfo.perfCounterLastCall.QuadPart;
-	curCounterFreq.QuadPart = timeInfo.curCounterFreq.QuadPart;
+	fileTimeLastCall = timeInfo.fileTimeLastCall.QuadPart;
+	perfCounterLastCall = timeInfo.perfCounterLastCall.QuadPart;
+	curCounterFreq = 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 (curCounter.QuadPart <= perfCounterLastCall) {
+	    /* Calibrated file-time is saved from posix in 100-ns ticks */
+	    return fileTimeLastCall / 10;
 	}
 
 	/*
@@ -602,15 +610,12 @@ NativeGetMicroseconds(void)
 	 * loop should recover.
 	 */
 
-	if (curCounter.QuadPart - perfCounterLastCall.QuadPart <
-		11 * curCounterFreq.QuadPart / 10
+	if (curCounter.QuadPart - perfCounterLastCall <
+		11 * curCounterFreq * timeInfo.calibrationInterv / 10
 	) {
-	    curFileTime = fileTimeLastCall.QuadPart +
-		 ((curCounter.QuadPart - perfCounterLastCall.QuadPart)
-		    * 10000000 / curCounterFreq.QuadPart);
-
-	    usecSincePosixEpoch = (curFileTime - posixEpoch.QuadPart) / 10;
-	    return usecSincePosixEpoch;
+	    /* Calibrated file-time is saved from posix in 100-ns ticks */
+	    return NativeCalc100NsTicks(fileTimeLastCall,
+		perfCounterLastCall, curCounterFreq, curCounter.QuadPart) / 10;
 	}
     }
 
@@ -681,6 +686,8 @@ NativeGetTime(
  *----------------------------------------------------------------------
  */
 
+void TclWinResetTimerResolution(void);
+
 static void
 StopCalibration(
     ClientData unused)		/* Client data is unused */
@@ -969,6 +976,8 @@ CalibrationThread(
     QueryPerformanceFrequency(&timeInfo.curCounterFreq);
     timeInfo.fileTimeLastCall.LowPart = curFileTime.dwLowDateTime;
     timeInfo.fileTimeLastCall.HighPart = curFileTime.dwHighDateTime;
+    /* Calibrated file-time will be saved from posix in 100-ns ticks */
+    timeInfo.fileTimeLastCall.QuadPart -= timeInfo.posixEpoch.QuadPart;
 
     ResetCounterSamples(timeInfo.fileTimeLastCall.QuadPart,
 	    timeInfo.perfCounterLastCall.QuadPart,
@@ -1028,6 +1037,7 @@ UpdateTimeEachSecond(void)
 				/* Current value returned from
 				 * QueryPerformanceCounter. */
     FILETIME curSysTime;	/* Current system time. */
+    static LARGE_INTEGER lastFileTime; /* File time of the previous calibration */
     LARGE_INTEGER curFileTime;	/* File time at the time this callback was
 				 * scheduled. */
     Tcl_WideInt estFreq;	/* Estimated perf counter frequency. */
@@ -1039,15 +1049,24 @@ UpdateTimeEachSecond(void)
 				 * step over 1 second. */
 
     /*
-     * Sample performance counter and system time.
+     * Sample performance counter and system time (from posix epoch).
      */
 
-    QueryPerformanceCounter(&curPerfCounter);
     GetSystemTimeAsFileTime(&curSysTime);
     curFileTime.LowPart = curSysTime.dwLowDateTime;
     curFileTime.HighPart = curSysTime.dwHighDateTime;
-
-    EnterCriticalSection(&timeInfo.cs);
+    curFileTime.QuadPart -= timeInfo.posixEpoch.QuadPart;
+    /* If calibration still not needed (check for possible time switch) */
+    if ( curFileTime.QuadPart > lastFileTime.QuadPart
+      && curFileTime.QuadPart < lastFileTime.QuadPart +
+      				    (timeInfo.calibrationInterv * 10000000)
+    ) {
+    	/* again in next one second */
+	return;
+    }
+    QueryPerformanceCounter(&curPerfCounter);
+    
+    lastFileTime.QuadPart = curFileTime.QuadPart;
 
     /*
      * We devide by timeInfo.curCounterFreq.QuadPart in several places. That
@@ -1059,7 +1078,6 @@ UpdateTimeEachSecond(void)
      */
 
     if (timeInfo.curCounterFreq.QuadPart == 0){
-	LeaveCriticalSection(&timeInfo.cs);
 	timeInfo.perfCounterAvailable = 0;
 	return;
     }
@@ -1098,12 +1116,9 @@ UpdateTimeEachSecond(void)
      * is estFreq * 20000000 / (vt1 - vt0)
      */
 
-    vt0 = 10000000 * (curPerfCounter.QuadPart
-		- timeInfo.perfCounterLastCall.QuadPart)
-	    / timeInfo.curCounterFreq.QuadPart
-	    + timeInfo.fileTimeLastCall.QuadPart;
-    vt1 = 20000000 + curFileTime.QuadPart;
-
+    vt0 = NativeCalc100NsTicks(timeInfo.fileTimeLastCall.QuadPart,
+	    timeInfo.perfCounterLastCall.QuadPart, timeInfo.curCounterFreq.QuadPart,
+	    curPerfCounter.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,
@@ -1112,21 +1127,75 @@ UpdateTimeEachSecond(void)
 
     tdiff = vt0 - curFileTime.QuadPart;
     if (tdiff > 10000000 || tdiff < -10000000) {
-	timeInfo.fileTimeLastCall.QuadPart = curFileTime.QuadPart;
-	timeInfo.curCounterFreq.QuadPart = estFreq;
+    	/* jump to current system time, use curent estimated frequency */
+    	vt0 = curFileTime.QuadPart;
     } else {
-	driftFreq = estFreq * 20000000 / (vt1 - vt0);
+    	/* calculate new frequency and estimate drift to the next second */
+	vt1 = 20000000 + curFileTime.QuadPart;
+	driftFreq = (estFreq * 20000000 / (vt1 - vt0));
+	/* 
+	 * Avoid too large drifts (only half of the current difference),
+	 * that allows also be more accurate (aspire to the smallest tdiff),
+	 * so then we can prolong calibration interval by tdiff < 100000
+	 */
+	driftFreq = timeInfo.curCounterFreq.QuadPart +
+		(driftFreq - timeInfo.curCounterFreq.QuadPart) / 2;
 
-	if (driftFreq > 1003*estFreq/1000) {
-	    driftFreq = 1003*estFreq/1000;
-	} else if (driftFreq < 997*estFreq/1000) {
-	    driftFreq = 997*estFreq/1000;
+	/* 
+	 * Average between estimated, 2 current and 5 drifted frequencies,
+	 * (do the soft drifting as possible)
+	 */
+	estFreq = (estFreq + 2 * timeInfo.curCounterFreq.QuadPart + 5 * driftFreq) / 8;
+    }
+    
+    /* Avoid too large discrepancy from nominal frequency */
+    if (estFreq > 1003*timeInfo.nominalFreq.QuadPart/1000) {
+	estFreq = 1003*timeInfo.nominalFreq.QuadPart/1000;
+	vt0 = curFileTime.QuadPart;
+    } else if (estFreq < 997*timeInfo.nominalFreq.QuadPart/1000) {
+	estFreq = 997*timeInfo.nominalFreq.QuadPart/1000;
+	vt0 = curFileTime.QuadPart;
+    } else if (vt0 != curFileTime.QuadPart) {
+	/* 
+	 * Be sure the clock ticks never backwards (avoid it by negative drifting)
+	 * just compare native time (in 100-ns) before and hereafter using 
+	 * new calibrated values) and do a small adjustment (short time freeze)
+	 */
+	LARGE_INTEGER newPerfCounter;
+	Tcl_WideInt nt0, nt1;
+
+	QueryPerformanceCounter(&newPerfCounter);
+	nt0 = NativeCalc100NsTicks(timeInfo.fileTimeLastCall.QuadPart,
+		timeInfo.perfCounterLastCall.QuadPart, timeInfo.curCounterFreq.QuadPart,
+		newPerfCounter.QuadPart);
+	nt1 = NativeCalc100NsTicks(vt0,
+		curPerfCounter.QuadPart, estFreq,
+		newPerfCounter.QuadPart);
+	if (nt0 > nt1) { /* drifted backwards, try to compensate with new base */
+	    /* first adjust with a micro jump (short frozen time is acceptable) */
+	    vt0 += nt0 - nt1;
+	    /* if drift unavoidable (e. g. we had a time switch), then reset it */
+	    vt1 = vt0 - curFileTime.QuadPart;
+	    if (vt1 > 10000000 || vt1 < -10000000) {
+	    	/* larger jump resp. shift relative new file-time */
+	    	vt0 = curFileTime.QuadPart;
+	    }
 	}
+    }
+
+    /* In lock commit new values to timeInfo (hold lock as short as possible) */
+    EnterCriticalSection(&timeInfo.cs);
 
-	timeInfo.fileTimeLastCall.QuadPart = vt0;
-	timeInfo.curCounterFreq.QuadPart = driftFreq;
+    /* grow calibration interval up to 10 seconds (if still precise enough) */
+    if (tdiff < -100000 || tdiff > 100000) {
+	/* too long drift - reset calibration interval to 1000 second */
+	timeInfo.calibrationInterv = 1;
+    } else if (timeInfo.calibrationInterv < 10) {
+	timeInfo.calibrationInterv++;
     }
 
+    timeInfo.fileTimeLastCall.QuadPart = vt0;
+    timeInfo.curCounterFreq.QuadPart = estFreq;
     timeInfo.perfCounterLastCall.QuadPart = curPerfCounter.QuadPart;
 
     LeaveCriticalSection(&timeInfo.cs);