Add test for qRound

Add test for qRound that covers some edge cases for rounding. Note that
as of right now, this test fails and the docs have been updated to warn
that it should not be depended on for strict correctness.

Change-Id: I1a61bca47abd77855fe7c13ded44e913cc7e8722
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

2 files changed, 64 insertions, 0 deletions

diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp
index bcfc6ada2e..ee857d61ac 100644
--- a/src/corelib/global/qglobal.cpp
+++ b/src/corelib/global/qglobal.cpp
@@ -968,6 +968,8 @@ static_assert((std::is_same<qsizetype, qptrdiff>::value));
 
     Rounds half away from zero (e.g. 0.5 -> 1, -0.5 -> -1).
 
+    \note This function does not guarantee correctness for high precisions.
+
     Example:
 
     \snippet code/src_corelib_global_qglobal.cpp 11A
@@ -980,6 +982,8 @@ static_assert((std::is_same<qsizetype, qptrdiff>::value));
 
     Rounds half away from zero (e.g. 0.5f -> 1, -0.5f -> -1).
 
+    \note This function does not guarantee correctness for high precisions.
+
     Example:
 
     \snippet code/src_corelib_global_qglobal.cpp 11B
@@ -992,6 +996,8 @@ static_assert((std::is_same<qsizetype, qptrdiff>::value));
 
     Rounds half away from zero (e.g. 0.5 -> 1, -0.5 -> -1).
 
+    \note This function does not guarantee correctness for high precisions.
+
     Example:
 
     \snippet code/src_corelib_global_qglobal.cpp 12A
@@ -1004,6 +1010,8 @@ static_assert((std::is_same<qsizetype, qptrdiff>::value));
 
     Rounds half away from zero (e.g. 0.5f -> 1, -0.5f -> -1).
 
+    \note This function does not guarantee correctness for high precisions.
+
     Example:
 
     \snippet code/src_corelib_global_qglobal.cpp 12B
diff --git a/tests/auto/corelib/global/qglobal/tst_qglobal.cpp b/tests/auto/corelib/global/qglobal/tst_qglobal.cpp
index 3c4bd3840e..032567cd39 100644
--- a/tests/auto/corelib/global/qglobal/tst_qglobal.cpp
+++ b/tests/auto/corelib/global/qglobal/tst_qglobal.cpp
@@ -33,6 +33,8 @@
 #include <QSysInfo>
 #include <QLatin1String>
 
+#include <cmath>
+
 class tst_QGlobal: public QObject
 {
     Q_OBJECT
@@ -52,6 +54,10 @@ private slots:
     void buildAbiEndianness();
     void testqOverload();
     void testqMinMax();
+    void qRoundFloats_data();
+    void qRoundFloats();
+    void qRoundDoubles_data();
+    void qRoundDoubles();
 };
 
 extern "C" {        // functions in qglobal.c
@@ -602,6 +608,56 @@ void tst_QGlobal::testqMinMax()
     compare(qMax(quint64(1), ushort(2)), quint64(2));
 }
 
+void tst_QGlobal::qRoundFloats_data()
+{
+    QTest::addColumn<float>("actual");
+    QTest::addColumn<float>("expected");
+
+    QTest::newRow("round half") << 0.5f << 1.0f;
+    QTest::newRow("round negative half") << -0.5f << -1.0f;
+    QTest::newRow("round negative") << -1.4f << -1.0f;
+    QTest::newRow("round largest representable float less than 0.5") << std::nextafter(0.5f, 0.0f) << 0.0f;
+}
+
+void tst_QGlobal::qRoundFloats() {
+    QFETCH(float, actual);
+    QFETCH(float, expected);
+
+    QEXPECT_FAIL("round largest representable float less than 0.5",
+                 "We know qRound fails in this case, but decided that we value simplicity over correctness",
+                 Continue);
+    QCOMPARE(qRound(actual), expected);
+
+    QEXPECT_FAIL("round largest representable float less than 0.5",
+                 "We know qRound fails in this case, but decided that we value simplicity over correctness",
+                 Continue);
+    QCOMPARE(qRound64(actual), expected);
+}
+
+void tst_QGlobal::qRoundDoubles_data() {
+    QTest::addColumn<double>("actual");
+    QTest::addColumn<double>("expected");
+
+    QTest::newRow("round half") << 0.5 << 1.0;
+    QTest::newRow("round negative half") << -0.5 << -1.0;
+    QTest::newRow("round negative") << -1.4 << -1.0;
+    QTest::newRow("round largest representable double less than 0.5") << std::nextafter(0.5, 0.0) << 0.0;
+}
+
+void tst_QGlobal::qRoundDoubles() {
+    QFETCH(double, actual);
+    QFETCH(double, expected);
+
+    QEXPECT_FAIL("round largest representable double less than 0.5",
+                 "We know qRound fails in this case, but decided that we value simplicity over correctness",
+                 Continue);
+    QCOMPARE(qRound(actual), expected);
+
+    QEXPECT_FAIL("round largest representable double less than 0.5",
+                 "We know qRound fails in this case, but decided that we value simplicity over correctness",
+                 Continue);
+    QCOMPARE(qRound64(actual), expected);
+}
 
 QTEST_APPLESS_MAIN(tst_QGlobal)
 #include "tst_qglobal.moc"