From b901129d9617508943f0a9e70ae6de14b10c8fec Mon Sep 17 00:00:00 2001
From: sebres <sebres@users.sourceforge.net>
Date: Mon, 2 Jan 2017 14:31:22 +0000
Subject: [win] bug fix in NativeGetTime: each call of it blurs current
 performance counters actualized in calibration thread in
 UpdateTimeEachSecond; This entails that sometimes sporadically time-drifts
 resp. jump-esque time-shifts occurred, what for example produces very
 confusing results during time measurement. [unix] wrong cast fixed in
 TclpGetWideClicks: multiplication with 1000000 in long int may cause overflow

See ticket b87ad7e9146832d505f9a430d779c5313c440256
---
 unix/tclUnixTime.c |  2 +-
 win/tclWinTime.c   | 54 +++++++++++++++++++++++++++++++++++++-----------------
 2 files changed, 38 insertions(+), 18 deletions(-)

diff --git a/unix/tclUnixTime.c b/unix/tclUnixTime.c
index df759d8..d634449 100644
--- a/unix/tclUnixTime.c
+++ b/unix/tclUnixTime.c
@@ -158,7 +158,7 @@ TclpGetWideClicks(void)
 	Tcl_Time time;
 
 	tclGetTimeProcPtr(&time, tclTimeClientData);
-	now = (Tcl_WideInt) (time.sec*1000000 + time.usec);
+	now = ((Tcl_WideInt)time.sec)*1000000 + time.usec;
     } else {
 #ifdef MAC_OSX_TCL
 	now = (Tcl_WideInt) (mach_absolute_time() & INT64_MAX);
diff --git a/win/tclWinTime.c b/win/tclWinTime.c
index 71a0366..8546c68 100644
--- a/win/tclWinTime.c
+++ b/win/tclWinTime.c
@@ -280,10 +280,6 @@ NativeGetTime(
     Tcl_Time *timePtr,
     ClientData clientData)
 {
-    struct _timeb t;
-    int useFtime = 1;		/* Flag == TRUE if we need to fall back on
-				 * ftime rather than using the perf counter. */
-
     /*
      * Initialize static storage on the first trip through.
      *
@@ -398,6 +394,10 @@ NativeGetTime(
 	 * 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
@@ -411,9 +411,29 @@ NativeGetTime(
 	posixEpoch.LowPart = 0xD53E8000;
 	posixEpoch.HighPart = 0x019DB1DE;
 
+	QueryPerformanceCounter(&curCounter);
+
+	/* 
+	 * Hold time section locked as short as possible
+	 */
 	EnterCriticalSection(&timeInfo.cs);
 
-	QueryPerformanceCounter(&curCounter);
+	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;
+	    timePtr->sec = (long) (usecSincePosixEpoch / 1000000);
+	    timePtr->usec = (unsigned long) (usecSincePosixEpoch % 1000000);
+	    return;
+	}
 
 	/*
 	 * If it appears to be more than 1.1 seconds since the last trip
@@ -425,31 +445,31 @@ NativeGetTime(
 	 * loop should recover.
 	 */
 
-	if (curCounter.QuadPart - timeInfo.perfCounterLastCall.QuadPart <
-		11 * timeInfo.curCounterFreq.QuadPart / 10) {
-	    curFileTime = timeInfo.fileTimeLastCall.QuadPart +
-		 ((curCounter.QuadPart - timeInfo.perfCounterLastCall.QuadPart)
-		    * 10000000 / timeInfo.curCounterFreq.QuadPart);
-	    timeInfo.fileTimeLastCall.QuadPart = curFileTime;
-	    timeInfo.perfCounterLastCall.QuadPart = curCounter.QuadPart;
+	if (curCounter.QuadPart - perfCounterLastCall.QuadPart <
+		11 * curCounterFreq.QuadPart / 10
+	) {
+	    curFileTime = fileTimeLastCall.QuadPart +
+		 ((curCounter.QuadPart - perfCounterLastCall.QuadPart)
+		    * 10000000 / curCounterFreq.QuadPart);
+
 	    usecSincePosixEpoch = (curFileTime - posixEpoch.QuadPart) / 10;
 	    timePtr->sec = (long) (usecSincePosixEpoch / 1000000);
 	    timePtr->usec = (unsigned long) (usecSincePosixEpoch % 1000000);
-	    useFtime = 0;
+	    return;
 	}
-
-	LeaveCriticalSection(&timeInfo.cs);
     }
 
-    if (useFtime) {
+    do {
 	/*
 	 * High resolution timer is not available. Just use ftime.
 	 */
+	struct _timeb t;
 
 	_ftime(&t);
 	timePtr->sec = (long)t.time;
 	timePtr->usec = t.millitm * 1000;
-    }
+
+    } while(0);
 }
 
 /*
-- 
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