QMap - improve docs a bit (mainly by adding more time complexities)

Change-Id: I8a361ef09c338bbba228fd774b2bfd938869adc5
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qmap.cpp

@@ -395,7 +395,7 @@ void QMapDataBase::freeData(QMapDataBase *d)
     differences are:
 
     \list
-    \li QHash provides faster lookups than QMap. (See \l{Algorithmic
+    \li QHash provides average faster lookups than QMap. (See \l{Algorithmic
        Complexity} for details.)
     \li When iterating over a QHash, the items are arbitrarily ordered.
        With QMap, the items are always sorted by key.
@@ -901,6 +901,8 @@ void QMapDataBase::freeData(QMapDataBase *d)
     Returns a reference to the smallest key in the map.
     This function assumes that the map is not empty.
 
+    This executes in \l{constant time}.
+
     \sa lastKey(), first(), isEmpty()
 */
 
@@ -909,6 +911,8 @@ void QMapDataBase::freeData(QMapDataBase *d)
     Returns a reference to the largest key in the map.
     This function assumes that the map is not empty.
 
+    This executes in \l{logarithmic time}.
+
     \sa firstKey(), last(), isEmpty()
 */
 
@@ -917,6 +921,8 @@ void QMapDataBase::freeData(QMapDataBase *d)
     Returns a reference to the first value in the map, that is the value mapped
     to the smallest key. This function assumes that the map is not empty.
 
+    When unshared (or const version is called), this executes in \l{constant time}.
+
     \sa last(), firstKey(), isEmpty()
 */
 
@@ -930,6 +936,8 @@ void QMapDataBase::freeData(QMapDataBase *d)
     Returns a reference to the last value in the map, that is the value mapped
     to the largest key. This function assumes that the map is not empty.
 
+    When unshared (or const version is called), this executes in \l{logarithmic time}.
+
     \sa first(), lastKey(), isEmpty()
 */
 
@@ -1057,8 +1065,11 @@ void QMapDataBase::freeData(QMapDataBase *d)
     If there are multiple items with the key \a key, then exactly one of them
     is replaced with \a value.
 
+    If the hint is correct and the map is unshared, the insert executes in amortized \l{constant time}.
+
     When creating a map from sorted data inserting the largest key first with constBegin()
-    is faster than inserting in sorted order with constEnd()
+    is faster than inserting in sorted order with constEnd(), since constEnd() - 1 (which is needed
+    to check if the hint is valid) needs \l{logarithmic time}.
 
     \b {Note:} Be careful with the hint. Providing an iterator from an older shared instance might
     crash but there is also a risk that it will silently corrupt both the map and the \a pos map.