Do not consider sign in qIsNull.

The current implementation of qIsNull only returns true if the value is
positive zero. This behaviour is not useful for use cases like
QPointF::isNull, where QPointF(-0, -0).isNull() will return false.
There doesn't seem to be a reason why the function exhibits this
behaviour (-0.0 is not accounted for in the unit tests), and for the
case of QSizeF::scale it causes a bug: qIsNull is used to check for
division by 0.0 before it proceeds, which fails in the case of -0.0.

Task-number: QTBUG-7303
Change-Id: I767e5280bd26614e8e78ae62b274eb9bc4ade385
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@nokia.com>

src/corelib/global/qglobal.h

@@ -813,7 +813,7 @@ Q_DECL_CONSTEXPR static inline bool qFuzzyIsNull(float f)
 /*
    This function tests a double for a null value. It doesn't
    check whether the actual value is 0 or close to 0, but whether
-   it is binary 0.
+   it is binary 0, disregarding sign.
 */
 static inline bool qIsNull(double d)
 {
@@ -823,13 +823,13 @@ static inline bool qIsNull(double d)
     };
     U val;
     val.d = d;
-    return val.u == quint64(0);
+    return (val.u & Q_UINT64_C(0x7fffffffffffffff)) == 0;
 }
 
 /*
    This function tests a float for a null value. It doesn't
    check whether the actual value is 0 or close to 0, but whether
-   it is binary 0.
+   it is binary 0, disregarding sign.
 */
 static inline bool qIsNull(float f)
 {
@@ -839,7 +839,7 @@ static inline bool qIsNull(float f)
     };
     U val;
     val.f = f;
-    return val.u == 0u;
+    return (val.u & 0x7fffffff) == 0;
 }
 
 /*

tests/auto/corelib/global/qglobal/tst_qglobal.cpp

@@ -72,6 +72,12 @@ void tst_QGlobal::qIsNull()
 
     QVERIFY(!::qIsNull(d));
     QVERIFY(!::qIsNull(f));
+
+    d = -0.0;
+    f = -0.0f;
+
+    QVERIFY(::qIsNull(d));
+    QVERIFY(::qIsNull(f));
 }
 
 void tst_QGlobal::for_each()

tests/auto/corelib/tools/qpointf/tst_qpointf.cpp

@@ -111,6 +111,11 @@ void tst_QPointF::isNull()
     QVERIFY(!point.isNull());
     point.rx() -= 2;
     QVERIFY(!point.isNull());
+
+    QPointF nullNegativeZero(qreal(-0.0), qreal(-0.0));
+    QCOMPARE(nullNegativeZero.x(), (qreal)-0.0f);
+    QCOMPARE(nullNegativeZero.y(), (qreal)-0.0f);
+    QVERIFY(nullNegativeZero.isNull());
 }
 
 void tst_QPointF::manhattanLength_data()

tests/auto/corelib/tools/qsizef/tst_qsizef.cpp

@@ -48,6 +48,9 @@ class tst_QSizeF : public QObject
 {
     Q_OBJECT
 private slots:
+    void isNull_data();
+    void isNull();
+
     void scale();
 
     void expandedTo();
@@ -60,6 +63,34 @@ private slots:
     void transpose();
 };
 
+void tst_QSizeF::isNull_data()
+{
+    QTest::addColumn<qreal>("width");
+    QTest::addColumn<qreal>("height");
+    QTest::addColumn<bool>("isNull");
+
+    QTest::newRow("0, 0") << qreal(0.0) << qreal(0.0) << true;
+    QTest::newRow("-0, -0") << qreal(-0.0) << qreal(-0.0) << true;
+    QTest::newRow("0, -0") << qreal(0) << qreal(-0.0) << true;
+    QTest::newRow("-0, 0") << qreal(-0.0) << qreal(0) << true;
+    QTest::newRow("-0.1, 0") << qreal(-0.1) << qreal(0) << false;
+    QTest::newRow("0, -0.1") << qreal(0) << qreal(-0.1) << false;
+    QTest::newRow("0.1, 0") << qreal(0.1) << qreal(0) << false;
+    QTest::newRow("0, 0.1") << qreal(0) << qreal(0.1) << false;
+}
+
+void tst_QSizeF::isNull()
+{
+    QFETCH(qreal, width);
+    QFETCH(qreal, height);
+    QFETCH(bool, isNull);
+
+    QSizeF size(width, height);
+    QCOMPARE(size.width(), width);
+    QCOMPARE(size.height(), height);
+    QCOMPARE(size.isNull(), isNull);
+}
+
 void tst_QSizeF::scale() {
     QSizeF t1(10.4, 12.8);
     t1.scale(60.6, 60.6, Qt::IgnoreAspectRatio);

tests/auto/gui/math3d/qquaternion/tst_qquaternion.cpp

@@ -116,6 +116,13 @@ void tst_QQuaternion::create()
     QCOMPARE(identity.scalar(), (qreal)1.0f);
     QVERIFY(identity.isIdentity());
 
+    QQuaternion negativeZeroIdentity(qreal(1.0), qreal(-0.0), qreal(-0.0), qreal(-0.0));
+    QCOMPARE(negativeZeroIdentity.x(), qreal(-0.0));
+    QCOMPARE(negativeZeroIdentity.y(), qreal(-0.0));
+    QCOMPARE(negativeZeroIdentity.z(), qreal(-0.0));
+    QCOMPARE(negativeZeroIdentity.scalar(), qreal(1.0));
+    QVERIFY(negativeZeroIdentity.isIdentity());
+
     QQuaternion v1(34.0f, 1.0f, 2.5f, -89.25f);
     QCOMPARE(v1.x(), (qreal)1.0f);
     QCOMPARE(v1.y(), (qreal)2.5f);

tests/auto/gui/math3d/qvectornd/tst_qvectornd.cpp

@@ -162,6 +162,11 @@ void tst_QVectorND::create2()
     QCOMPARE(null.y(), (qreal)0.0f);
     QVERIFY(null.isNull());
 
+    QVector2D nullNegativeZero(qreal(-0.0), qreal(-0.0));
+    QCOMPARE(nullNegativeZero.x(), (qreal)-0.0f);
+    QCOMPARE(nullNegativeZero.y(), (qreal)-0.0f);
+    QVERIFY(nullNegativeZero.isNull());
+
     QVector2D v1(1.0f, 2.5f);
     QCOMPARE(v1.x(), (qreal)1.0f);
     QCOMPARE(v1.y(), (qreal)2.5f);
@@ -252,6 +257,12 @@ void tst_QVectorND::create3()
     QCOMPARE(null.z(), (qreal)0.0f);
     QVERIFY(null.isNull());
 
+    QVector3D nullNegativeZero(qreal(-0.0), qreal(-0.0), qreal(-0.0));
+    QCOMPARE(nullNegativeZero.x(), (qreal)-0.0f);
+    QCOMPARE(nullNegativeZero.y(), (qreal)-0.0f);
+    QCOMPARE(nullNegativeZero.z(), (qreal)-0.0f);
+    QVERIFY(nullNegativeZero.isNull());
+
     QVector3D v1(1.0f, 2.5f, -89.25f);
     QCOMPARE(v1.x(), (qreal)1.0f);
     QCOMPARE(v1.y(), (qreal)2.5f);
@@ -379,6 +390,13 @@ void tst_QVectorND::create4()
     QCOMPARE(null.w(), (qreal)0.0f);
     QVERIFY(null.isNull());
 
+    QVector4D nullNegativeZero(qreal(-0.0), qreal(-0.0), qreal(-0.0), qreal(-0.0));
+    QCOMPARE(nullNegativeZero.x(), (qreal)-0.0f);
+    QCOMPARE(nullNegativeZero.y(), (qreal)-0.0f);
+    QCOMPARE(nullNegativeZero.z(), (qreal)-0.0f);
+    QCOMPARE(nullNegativeZero.w(), (qreal)-0.0f);
+    QVERIFY(nullNegativeZero.isNull());
+
     QVector4D v1(1.0f, 2.5f, -89.25f, 34.0f);
     QCOMPARE(v1.x(), (qreal)1.0f);
     QCOMPARE(v1.y(), (qreal)2.5f);