[libcxx] Avoid overflows in the windows __libcpp_steady_clock_now()
As freq.QuadValue can be in the range of 10000000 to 19200000,
the multiplication before division makes the calculation overflow
and wrap to negative values every 16-30 minutes.
Instead count the whole seconds separately before adding the
scaled fractional seconds.
Add a testcase for steady_clock to check that the values returned for
now() compare as bigger than the zero time origin; this
corresponds to a testcase in Qt [1] [2] (that failed spuriously
due to this).
[1] https://bugreports.qt.io/browse/QTBUG-89539
[2] https://code.qt.io/cgit/qt/qtbase.git/tree/tests/auto/corelib/kernel/qdeadlinetimer/tst_qdeadlinetimer.cpp?id=f8de5e54022b8b7471131b7ad55c83b69b2684c0#n569
Differential Revision: https://reviews.llvm.org/D93456
GitOrigin-RevId: 02f1d28ed6b8f33445dae3beed8b6cc8dada4312
diff --git a/src/chrono.cpp b/src/chrono.cpp
index 1419cf2..5291d4f 100644
--- a/src/chrono.cpp
+++ b/src/chrono.cpp
@@ -153,7 +153,10 @@
LARGE_INTEGER counter;
(void) QueryPerformanceCounter(&counter);
- return steady_clock::time_point(steady_clock::duration(counter.QuadPart * nano::den / freq.QuadPart));
+ auto seconds = counter.QuadPart / freq.QuadPart;
+ auto fractions = counter.QuadPart % freq.QuadPart;
+ auto dur = seconds * nano::den + fractions * nano::den / freq.QuadPart;
+ return steady_clock::time_point(steady_clock::duration(dur));
}
#elif defined(CLOCK_MONOTONIC)