QMap 5.0 - keep track of leftmost node (BIC)

This suggestion keeps track of the most left node.
The point is that constBegin() becomes a lot faster.

That speeds up iteration a bit, and makes it O(1) to get the
first element. The penalty in insert and remove is very small.
On large trees it seems to be less than 1%.

It should be noticed that constBegin() is a very common hint
on my planned change to 5.1, and this opperation will without
this patch cost 2 x log N. One when the user calls the hint
with begin - and one where it is compared with begin.

Other std::maps has a very fast begin(). E.g
http://www.cplusplus.com/reference/stl/map/begin/
(begin with constant time)

Change-Id: I221f6755aa8bd16a5189771c5bc8ae56c8ee0fb4
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 93 insertions, 1 deletions

diff --git a/tests/auto/corelib/tools/qmap/tst_qmap.cpp b/tests/auto/corelib/tools/qmap/tst_qmap.cpp
index e07b3fc81e..9c53563a5c 100644
--- a/tests/auto/corelib/tools/qmap/tst_qmap.cpp
+++ b/tests/auto/corelib/tools/qmap/tst_qmap.cpp
@@ -49,6 +49,9 @@
 class tst_QMap : public QObject
 {
     Q_OBJECT
+protected:
+    template <class KEY, class VALUE>
+    void sanityCheckTree(const QMap<KEY, VALUE> &m, int calledFromLine);
 public slots:
     void init();
 private slots:
@@ -79,6 +82,7 @@ private slots:
     void setSharable();
 
     void insert();
+    void checkMostLeftNode();
 };
 
 typedef QMap<QString, QString> StringMap;
@@ -115,6 +119,28 @@ QDebug operator << (QDebug d, const MyClass &c) {
     return d;
 }
 
+template <class KEY, class VALUE>
+void tst_QMap::sanityCheckTree(const QMap<KEY, VALUE> &m, int calledFromLine)
+{
+    QString possibleFrom;
+    possibleFrom.setNum(calledFromLine);
+    possibleFrom = "Called from line: " + possibleFrom;
+    int count = 0;
+    typename QMap<KEY, VALUE>::const_iterator oldite = m.constBegin();
+    for (typename QMap<KEY, VALUE>::const_iterator i = m.constBegin(); i != m.constEnd(); ++i) {
+        count++;
+        bool oldIteratorIsLarger = i.key() < oldite.key();
+        QVERIFY2(!oldIteratorIsLarger, possibleFrom.toUtf8());
+        oldite = i;
+    }
+    if (m.size() != count) { // Fail
+        qDebug() << possibleFrom;
+        QCOMPARE(m.size(), count);
+    }
+    if (m.size() == 0)
+        QVERIFY(m.constBegin() == m.constEnd());
+}
+
 void tst_QMap::init()
 {
     MyClass::count = 0;
@@ -280,6 +306,7 @@ void tst_QMap::clear()
         map.insert( "key0", MyClass( "value1" ) );
         map.insert( "key1", MyClass( "value2" ) );
         map.clear();
+        sanityCheckTree(map, __LINE__);
         QVERIFY( map.isEmpty() );
     }
     QCOMPARE( MyClass::count, int(0) );
@@ -400,6 +427,8 @@ void tst_QMap::swap()
     m1.swap(m2);
     QCOMPARE(m1.value(1),QLatin1String("m2[1]"));
     QCOMPARE(m2.value(0),QLatin1String("m1[0]"));
+    sanityCheckTree(m1, __LINE__);
+    sanityCheckTree(m2, __LINE__);
 }
 
 void tst_QMap::operator_eq()
@@ -631,7 +660,7 @@ void tst_QMap::lowerUpperBound()
 
 void tst_QMap::mergeCompare()
 {
-    QMap<int, QString> map1, map2, map3;
+    QMap<int, QString> map1, map2, map3, map1b, map2b;
 
     map1.insert(1,"ett");
     map1.insert(3,"tre");
@@ -641,6 +670,13 @@ void tst_QMap::mergeCompare()
     map2.insert(4,"fyra");
 
     map1.unite(map2);
+    sanityCheckTree(map1, __LINE__);
+
+    map1b = map1;
+    map2b = map2;
+    map2b.insert(0, "nul");
+    map1b.unite(map2b);
+    sanityCheckTree(map1b, __LINE__);
 
     QVERIFY(map1.value(1) == "ett");
     QVERIFY(map1.value(2) == "tvo");
@@ -958,9 +994,11 @@ void tst_QMap::setSharable()
 
         QVERIFY(!map.isDetached());
         QVERIFY(copy.isSharedWith(map));
+        sanityCheckTree(copy, __LINE__);
     }
 
     map.setSharable(false);
+    sanityCheckTree(map, __LINE__);
     QVERIFY(map.isDetached());
     QCOMPARE(map.size(), 4);
     QCOMPARE(const_(map)[4], QString("quatro"));
@@ -975,6 +1013,8 @@ void tst_QMap::setSharable()
         QCOMPARE(const_(copy)[4], QString("quatro"));
 
         QCOMPARE(map, copy);
+        sanityCheckTree(map, __LINE__);
+        sanityCheckTree(copy, __LINE__);
     }
 
     map.setSharable(true);
@@ -1012,5 +1052,57 @@ void tst_QMap::insert()
     }
 }
 
+void tst_QMap::checkMostLeftNode()
+{
+    QMap<int, int> map;
+
+    map.insert(100, 1);
+    sanityCheckTree(map, __LINE__);
+
+    // insert
+    map.insert(99, 1);
+    sanityCheckTree(map, __LINE__);
+    map.insert(98, 1);
+    sanityCheckTree(map, __LINE__);
+    map.insert(97, 1);
+    sanityCheckTree(map, __LINE__);
+    map.insert(96, 1);
+    sanityCheckTree(map, __LINE__);
+    map.insert(95, 1);
+
+    // remove
+    sanityCheckTree(map, __LINE__);
+    map.take(95);
+    sanityCheckTree(map, __LINE__);
+    map.remove(96);
+    sanityCheckTree(map, __LINE__);
+    map.erase(map.begin());
+    sanityCheckTree(map, __LINE__);
+    map.remove(97);
+    sanityCheckTree(map, __LINE__);
+    map.remove(98);
+    sanityCheckTree(map, __LINE__);
+    map.remove(99);
+    sanityCheckTree(map, __LINE__);
+    map.remove(100);
+    sanityCheckTree(map, __LINE__);
+    map.insert(200, 1);
+    QCOMPARE(map.constBegin().key(), 200);
+    sanityCheckTree(map, __LINE__);
+    // remove the non left most node
+    map.insert(202, 2);
+    map.insert(203, 3);
+    map.insert(204, 4);
+    map.remove(202);
+    sanityCheckTree(map, __LINE__);
+    map.remove(203);
+    sanityCheckTree(map, __LINE__);
+    map.remove(204);
+    sanityCheckTree(map, __LINE__);
+    // erase last item
+    map.erase(map.begin());
+    sanityCheckTree(map, __LINE__);
+}
+
 QTEST_APPLESS_MAIN(tst_QMap)
 #include "tst_qmap.moc"