QTimerInfo/Unix: Fix roundToMillisecond when it's already rounded

Don't add 1 ms when it's rounded to 1 ms.

Found when running unit tests on QNX, where the clock did not update
between two subsequent calls to clock_gettime().

All of this ought to be refactored to use std::chrono::nanoseconds.

Fixes: QTBUG-100438
Pick-to: 6.2 6.3
Change-Id: I47dc6426c33d3a66dec946ae3589694745ed1835
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

2 files changed, 20 insertions, 13 deletions

diff --git a/src/corelib/kernel/qcore_unix_p.h b/src/corelib/kernel/qcore_unix_p.h
index abe9bb3738..23c20b1749 100644
--- a/src/corelib/kernel/qcore_unix_p.h
+++ b/src/corelib/kernel/qcore_unix_p.h
@@ -105,7 +105,7 @@ QT_BEGIN_NAMESPACE
 Q_DECLARE_TYPEINFO(pollfd, Q_PRIMITIVE_TYPE);
 
 // Internal operator functions for timespecs
-inline timespec &normalizedTimespec(timespec &t)
+constexpr inline timespec &normalizedTimespec(timespec &t)
 {
     while (t.tv_nsec >= 1000000000) {
         ++t.tv_sec;
@@ -117,35 +117,35 @@ inline timespec &normalizedTimespec(timespec &t)
     }
     return t;
 }
-inline bool operator<(const timespec &t1, const timespec &t2)
+constexpr inline bool operator<(const timespec &t1, const timespec &t2)
 { return t1.tv_sec < t2.tv_sec || (t1.tv_sec == t2.tv_sec && t1.tv_nsec < t2.tv_nsec); }
-inline bool operator==(const timespec &t1, const timespec &t2)
+constexpr inline bool operator==(const timespec &t1, const timespec &t2)
 { return t1.tv_sec == t2.tv_sec && t1.tv_nsec == t2.tv_nsec; }
-inline bool operator!=(const timespec &t1, const timespec &t2)
+constexpr inline bool operator!=(const timespec &t1, const timespec &t2)
 { return !(t1 == t2); }
-inline timespec &operator+=(timespec &t1, const timespec &t2)
+constexpr inline timespec &operator+=(timespec &t1, const timespec &t2)
 {
     t1.tv_sec += t2.tv_sec;
     t1.tv_nsec += t2.tv_nsec;
     return normalizedTimespec(t1);
 }
-inline timespec operator+(const timespec &t1, const timespec &t2)
+constexpr inline timespec operator+(const timespec &t1, const timespec &t2)
 {
-    timespec tmp;
+    timespec tmp = {};
     tmp.tv_sec = t1.tv_sec + t2.tv_sec;
     tmp.tv_nsec = t1.tv_nsec + t2.tv_nsec;
     return normalizedTimespec(tmp);
 }
-inline timespec operator-(const timespec &t1, const timespec &t2)
+constexpr inline timespec operator-(const timespec &t1, const timespec &t2)
 {
-    timespec tmp;
+    timespec tmp = {};
     tmp.tv_sec = t1.tv_sec - (t2.tv_sec - 1);
     tmp.tv_nsec = t1.tv_nsec - (t2.tv_nsec + 1000000000);
     return normalizedTimespec(tmp);
 }
-inline timespec operator*(const timespec &t1, int mul)
+constexpr inline timespec operator*(const timespec &t1, int mul)
 {
-    timespec tmp;
+    timespec tmp = {};
     tmp.tv_sec = t1.tv_sec * mul;
     tmp.tv_nsec = t1.tv_nsec * mul;
     return normalizedTimespec(tmp);
diff --git a/src/corelib/kernel/qtimerinfo_unix.cpp b/src/corelib/kernel/qtimerinfo_unix.cpp
index db4d4b1188..3b1696647b 100644
--- a/src/corelib/kernel/qtimerinfo_unix.cpp
+++ b/src/corelib/kernel/qtimerinfo_unix.cpp
@@ -197,15 +197,22 @@ inline timespec operator+(const timespec &t1, int ms)
     return t2 += ms;
 }
 
-static timespec roundToMillisecond(timespec val)
+static constexpr timespec roundToMillisecond(timespec val)
 {
     // always round up
     // worst case scenario is that the first trigger of a 1-ms timer is 0.999 ms late
 
     int ns = val.tv_nsec % (1000 * 1000);
-    val.tv_nsec += 1000 * 1000 - ns;
+    if (ns)
+        val.tv_nsec += 1000 * 1000 - ns;
     return normalizedTimespec(val);
 }
+static_assert(roundToMillisecond({0, 0}) == timespec{0, 0});
+static_assert(roundToMillisecond({0, 1}) == timespec{0, 1'000'000});
+static_assert(roundToMillisecond({0, 999'999}) == timespec{0, 1'000'000});
+static_assert(roundToMillisecond({0, 1'000'000}) == timespec{0, 1'000'000});
+static_assert(roundToMillisecond({0, 999'999'999}) == timespec{1, 0});
+static_assert(roundToMillisecond({1, 0}) == timespec{1, 0});
 
 #ifdef QTIMERINFO_DEBUG
 QDebug operator<<(QDebug s, timeval tv)