From f3b6963f8b873c190cc1033cb8dabaf1d63ee2b6 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@kdab.com>
Date: Sat, 27 Jul 2019 16:32:28 +0300
Subject: QEventFilterService: these aren't the algorithms you're looking for

The event filters are ordered by priority, so don't use a linear scan
in order to find whether one with the same position already exists,
use lower_bound, whose result at the same time gives the position of
an existing filter (if any), as well as the insertion position for the
new element. So no need to do a full sort afterwards, either.

Change the exisitng op< into an aptly-named lambda, and don't depend on
transitive includes.

Also, since this code does not need the CoW feature of QVector, port to
std::vector, which is faster and produces more compact code.

Altogether saves ~2KiB (0.47%) in text size on optimized Linux AMD64
GCC 9.1 builds.

Change-Id: Ie46ca2fbb2dcbea23a0098a72336604776dcc296
Reviewed-by: Mike Krus <mike.krus@kdab.com>
---
 src/core/services/qeventfilterservice.cpp | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/src/core/services/qeventfilterservice.cpp b/src/core/services/qeventfilterservice.cpp
index 4855d69ed..036bcd7b4 100644
--- a/src/core/services/qeventfilterservice.cpp
+++ b/src/core/services/qeventfilterservice.cpp
@@ -40,10 +40,12 @@
 #include "qeventfilterservice_p.h"
 
 #include <QtCore/QObject>
-#include <QtCore/QVector>
 
 #include <Qt3DCore/private/qabstractserviceprovider_p.h>
 
+#include <algorithm>
+#include <vector>
+
 QT_BEGIN_NAMESPACE
 
 namespace {
@@ -53,10 +55,10 @@ namespace {
         int priority;
     };
 
-    bool operator <(const FilterPriorityPair &a, const FilterPriorityPair &b)
+    const auto byPriority = [](const FilterPriorityPair &a, const FilterPriorityPair &b) noexcept
     {
         return a.priority < b.priority;
-    }
+    };
 }
 
 Q_DECLARE_TYPEINFO(FilterPriorityPair, Q_PRIMITIVE_TYPE);
@@ -88,32 +90,26 @@ public:
 
     void registerEventFilter(QObject *eventFilter, int priority)
     {
-        for (int i = 0, m = m_eventFilters.size(); i < m; ++i)
-            if (m_eventFilters.at(i).priority == priority)
-                return;
-
         FilterPriorityPair fpPair;
         fpPair.filter = eventFilter;
         fpPair.priority = priority;
-        m_eventFilters.push_back(fpPair);
-        std::sort(m_eventFilters.begin(), m_eventFilters.end());
+        const auto it = std::lower_bound(m_eventFilters.begin(), m_eventFilters.end(), fpPair, byPriority);
+        if (it == m_eventFilters.end() || it->priority != priority)
+            m_eventFilters.insert(it, std::move(fpPair));
     }
 
     void unregisterEventFilter(QObject *eventFilter)
     {
-        QVector<FilterPriorityPair>::iterator it = m_eventFilters.begin();
-        const QVector<FilterPriorityPair>::iterator end = m_eventFilters.end();
-        while (it != end) {
+        for (auto it = m_eventFilters.begin(), end = m_eventFilters.end(); it != end; ++it) {
             if (it->filter == eventFilter) {
                 m_eventFilters.erase(it);
                 return;
             }
-            ++it;
         }
     }
 
     QScopedPointer<InternalEventListener> m_eventDispatcher;
-    QVector<FilterPriorityPair> m_eventFilters;
+    std::vector<FilterPriorityPair> m_eventFilters;
 };
 
 /* !\internal
@@ -178,8 +174,8 @@ InternalEventListener::InternalEventListener(QEventFilterServicePrivate *filterS
 
 bool InternalEventListener::eventFilter(QObject *obj, QEvent *e)
 {
-    for (int i = m_filterService->m_eventFilters.size() - 1; i >= 0; --i) {
-        const FilterPriorityPair &fPPair = m_filterService->m_eventFilters.at(i);
+    for (auto i = m_filterService->m_eventFilters.size(); i > 0; --i) {
+        const FilterPriorityPair &fPPair = m_filterService->m_eventFilters[i - 1];
         if (fPPair.filter->eventFilter(obj, e))
             return true;
     }
-- 
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