Revert "Win32: always use the performance timers (fix #3918)"

This reverts commit 6e0595fd.

src/misc/mtime.c

@@ -221,20 +221,112 @@ mtime_t mdate( void )
 
     /* Convert to microseconds */
     res = date / 1000;
-
 #elif defined( WIN32 ) || defined( UNDER_CE )
     /* We don't need the real date, just the value of a high precision timer */
-    LARGE_INTEGER counter, freq;
-    if (!QueryPerformanceCounter (&counter)
-     || !QueryPerformanceFrequency (&freq))
-        abort();
+    static mtime_t freq = INT64_C(-1);
 
-    /* Convert to from (1/freq) to microsecond resolution */
-    /* We need to split the division to avoid 63-bits overflow */
-    lldiv_t d = lldiv (counter.QuadPart, freq.QuadPart);
+    if( freq == INT64_C(-1) )
+    {
+        /* Extract from the Tcl source code:
+         * (http://www.cs.man.ac.uk/fellowsd-bin/TIP/7.html)
+         *
+         * 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.  If it's anything else, we
+         * presume that the performance counter is unreliable.
+         */
+        LARGE_INTEGER buf;
+
+        freq = ( QueryPerformanceFrequency( &buf ) &&
+                 (buf.QuadPart == INT64_C(1193182) || buf.QuadPart == INT64_C(3579545) ) )
+               ? buf.QuadPart : 0;
+
+#if defined( WIN32 )
+        /* on windows 2000, XP and Vista detect if there are two
+           cores there - that makes QueryPerformanceFrequency in
+           any case not trustable?
+           (may also be true, for single cores with adaptive
+            CPU frequency and active power management?)
+        */
+        HINSTANCE h_Kernel32 = LoadLibrary(_T("kernel32.dll"));
+        if(h_Kernel32)
+        {
+            void WINAPI (*pf_GetSystemInfo)(LPSYSTEM_INFO);
+            pf_GetSystemInfo = (void WINAPI (*)(LPSYSTEM_INFO))
+                                GetProcAddress(h_Kernel32, _T("GetSystemInfo"));
+            if(pf_GetSystemInfo)
+            {
+               SYSTEM_INFO system_info;
+               pf_GetSystemInfo(&system_info);
+               if(system_info.dwNumberOfProcessors > 1)
+                  freq = 0;
+            }
+            FreeLibrary(h_Kernel32);
+        }
+#endif
+    }
 
-    res = (d.quot * 1000000) + ((d.rem * 1000000) / freq.QuadPart);
+    if( freq != 0 )
+    {
+        LARGE_INTEGER counter;
+        QueryPerformanceCounter (&counter);
+
+        /* Convert to from (1/freq) to microsecond resolution */
+        /* We need to split the division to avoid 63-bits overflow */
+        lldiv_t d = lldiv (counter.QuadPart, freq);
 
+        res = (d.quot * 1000000) + ((d.rem * 1000000) / freq);
+    }
+    else
+    {
+        /* Fallback on timeGetTime() which has a millisecond resolution
+         * (actually, best case is about 5 ms resolution)
+         * timeGetTime() only returns a DWORD thus will wrap after
+         * about 49.7 days so we try to detect the wrapping. */
+
+        static CRITICAL_SECTION date_lock;
+        static mtime_t i_previous_time = INT64_C(-1);
+        static int i_wrap_counts = -1;
+
+        if( i_wrap_counts == -1 )
+        {
+            /* Initialization */
+#if defined( WIN32 )
+            i_previous_time = INT64_C(1000) * timeGetTime();
+#else
+            i_previous_time = INT64_C(1000) * GetTickCount();
+#endif
+            InitializeCriticalSection( &date_lock );
+            i_wrap_counts = 0;
+        }
+
+        EnterCriticalSection( &date_lock );
+#if defined( WIN32 )
+        res = INT64_C(1000) *
+            (i_wrap_counts * INT64_C(0x100000000) + timeGetTime());
+#else
+        res = INT64_C(1000) *
+            (i_wrap_counts * INT64_C(0x100000000) + GetTickCount());
+#endif
+        if( i_previous_time > res )
+        {
+            /* Counter wrapped */
+            i_wrap_counts++;
+            res += INT64_C(0x100000000) * 1000;
+        }
+        i_previous_time = res;
+        LeaveCriticalSection( &date_lock );
+    }
 #elif defined(USE_APPLE_MACH)
     /* The version that should be used, if it was cancelable */
     pthread_once(&mtime_timebase_info_once, mtime_init_timebase);