_q_interpolate<T> is unsafe with unsigned template arguments

_q_interpolate<T> subtracts 2 arguments of type T,
for unsigned types this can cause wrapping around

Task-number: QTBUG-57925
Change-Id: Iffa59f413579a3d5de8cb728fe71443d8e8a04aa
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

2 files changed, 38 insertions, 1 deletions

diff --git a/src/corelib/animation/qvariantanimation_p.h b/src/corelib/animation/qvariantanimation_p.h
index 37318a5339..9f0f2e3030 100644
--- a/src/corelib/animation/qvariantanimation_p.h
+++ b/src/corelib/animation/qvariantanimation_p.h
@@ -58,6 +58,8 @@
 
 #include "private/qabstractanimation_p.h"
 
+#include <type_traits>
+
 #ifndef QT_NO_ANIMATION
 
 QT_BEGIN_NAMESPACE
@@ -104,7 +106,17 @@ public:
 };
 
 //this should make the interpolation faster
-template<typename T> inline T _q_interpolate(const T &f, const T &t, qreal progress)
+template<typename T>
+typename std::enable_if<std::is_unsigned<T>::value, T>::type
+_q_interpolate(const T &f, const T &t, qreal progress)
+{
+    return T(f + t * progress - f * progress);
+}
+
+// the below will apply also to all non-arithmetic types
+template<typename T>
+typename std::enable_if<!std::is_unsigned<T>::value, T>::type
+_q_interpolate(const T &f, const T &t, qreal progress)
 {
     return T(f + (t - f) * progress);
 }
diff --git a/tests/auto/corelib/animation/qvariantanimation/tst_qvariantanimation.cpp b/tests/auto/corelib/animation/qvariantanimation/tst_qvariantanimation.cpp
index 00962afa72..ac20fb35ec 100644
--- a/tests/auto/corelib/animation/qvariantanimation/tst_qvariantanimation.cpp
+++ b/tests/auto/corelib/animation/qvariantanimation/tst_qvariantanimation.cpp
@@ -43,6 +43,7 @@ private slots:
     void keyValueAt();
     void keyValues();
     void duration();
+    void interpolation();
 };
 
 class TestableQVariantAnimation : public QVariantAnimation
@@ -129,6 +130,30 @@ void tst_QVariantAnimation::duration()
     QCOMPARE(anim.duration(), 500);
 }
 
+void tst_QVariantAnimation::interpolation()
+{
+    QVariantAnimation unsignedAnim;
+    unsignedAnim.setStartValue(100u);
+    unsignedAnim.setEndValue(0u);
+    unsignedAnim.setDuration(100);
+    unsignedAnim.setCurrentTime(50);
+    QCOMPARE(unsignedAnim.currentValue().toUInt(), 50u);
+
+    QVariantAnimation signedAnim;
+    signedAnim.setStartValue(100);
+    signedAnim.setEndValue(0);
+    signedAnim.setDuration(100);
+    signedAnim.setCurrentTime(50);
+    QCOMPARE(signedAnim.currentValue().toInt(), 50);
+
+    QVariantAnimation pointAnim;
+    pointAnim.setStartValue(QPoint(100, 100));
+    pointAnim.setEndValue(QPoint(0, 0));
+    pointAnim.setDuration(100);
+    pointAnim.setCurrentTime(50);
+    QCOMPARE(pointAnim.currentValue().toPoint(), QPoint(50, 50));
+}
+
 QTEST_MAIN(tst_QVariantAnimation)
 
 #include "tst_qvariantanimation.moc"