Speed up QTimeZone::isTimeZoneIdAvailable by a factor 43

Creating and sorting a list of bytearrays just to check if one entry is
present, is really overkill. By adding a new virtual method
isTimeZoneIdAvailable() in the backend classes, we can do this much more
efficiently.

Implemented for Utc and Tz backends, the others fall back to the
slow way.

The new benchmark shows, in release mode:
Before: 43 msecs per iteration (total: 86, iterations: 2)
After: 1.1 msecs per iteration (total: 73, iterations: 64)

Change-Id: Ic0d79a41d74e2ce6aa088fa7986c41d33902c36b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

4 files changed, 28 insertions, 2 deletions

diff --git a/src/corelib/tools/qtimezone.cpp b/src/corelib/tools/qtimezone.cpp
index 445ddeb31d..db6be581ec 100644
--- a/src/corelib/tools/qtimezone.cpp
+++ b/src/corelib/tools/qtimezone.cpp
@@ -820,8 +820,8 @@ bool QTimeZone::isTimeZoneIdAvailable(const QByteArray &ianaId)
     // IDs as availableTimeZoneIds() may be slow
     if (!QTimeZonePrivate::isValidId(ianaId))
         return false;
-    const QList<QByteArray> tzIds = availableTimeZoneIds();
-    return std::binary_search(tzIds.begin(), tzIds.end(), ianaId);
+    return QUtcTimeZonePrivate().isTimeZoneIdAvailable(ianaId) ||
+           global_tz->backend->isTimeZoneIdAvailable(ianaId);
 }
 
 static QList<QByteArray> set_union(const QList<QByteArray> &l1, const QList<QByteArray> &l2)
diff --git a/src/corelib/tools/qtimezoneprivate.cpp b/src/corelib/tools/qtimezoneprivate.cpp
index 1a5135f103..2b6c2ea6a5 100644
--- a/src/corelib/tools/qtimezoneprivate.cpp
+++ b/src/corelib/tools/qtimezoneprivate.cpp
@@ -486,6 +486,13 @@ QByteArray QTimeZonePrivate::systemTimeZoneId() const
     return QByteArray();
 }
 
+bool QTimeZonePrivate::isTimeZoneIdAvailable(const QByteArray& ianaId) const
+{
+    // Fall-back implementation, can be made faster in subclasses
+    const QList<QByteArray> tzIds = availableTimeZoneIds();
+    return std::binary_search(tzIds.begin(), tzIds.end(), ianaId);
+}
+
 QList<QByteArray> QTimeZonePrivate::availableTimeZoneIds() const
 {
     return QList<QByteArray>();
@@ -864,6 +871,17 @@ QByteArray QUtcTimeZonePrivate::systemTimeZoneId() const
     return utcQByteArray();
 }
 
+bool QUtcTimeZonePrivate::isTimeZoneIdAvailable(const QByteArray &ianaId) const
+{
+    for (int i = 0; i < utcDataTableSize; ++i) {
+        const QUtcData *data = utcData(i);
+        if (utcId(data) == ianaId) {
+            return true;
+        }
+    }
+    return false;
+}
+
 QList<QByteArray> QUtcTimeZonePrivate::availableTimeZoneIds() const
 {
     QList<QByteArray> result;
diff --git a/src/corelib/tools/qtimezoneprivate_p.h b/src/corelib/tools/qtimezoneprivate_p.h
index 4d357111f2..c9a5726216 100644
--- a/src/corelib/tools/qtimezoneprivate_p.h
+++ b/src/corelib/tools/qtimezoneprivate_p.h
@@ -128,6 +128,7 @@ public:
 
     virtual QByteArray systemTimeZoneId() const;
 
+    virtual bool isTimeZoneIdAvailable(const QByteArray &ianaId) const;
     virtual QList<QByteArray> availableTimeZoneIds() const;
     virtual QList<QByteArray> availableTimeZoneIds(QLocale::Country country) const;
     virtual QList<QByteArray> availableTimeZoneIds(int utcOffset) const;
@@ -204,6 +205,7 @@ public:
 
     QByteArray systemTimeZoneId() const override;
 
+    bool isTimeZoneIdAvailable(const QByteArray &ianaId) const override;
     QList<QByteArray> availableTimeZoneIds() const override;
     QList<QByteArray> availableTimeZoneIds(QLocale::Country country) const override;
     QList<QByteArray> availableTimeZoneIds(int utcOffset) const override;
@@ -323,6 +325,7 @@ public:
 
     QByteArray systemTimeZoneId() const override;
 
+    bool isTimeZoneIdAvailable(const QByteArray &ianaId) const override;
     QList<QByteArray> availableTimeZoneIds() const override;
     QList<QByteArray> availableTimeZoneIds(QLocale::Country country) const override;
 
diff --git a/src/corelib/tools/qtimezoneprivate_tz.cpp b/src/corelib/tools/qtimezoneprivate_tz.cpp
index 6a5df6272a..f1735a80e7 100644
--- a/src/corelib/tools/qtimezoneprivate_tz.cpp
+++ b/src/corelib/tools/qtimezoneprivate_tz.cpp
@@ -1098,6 +1098,11 @@ QByteArray QTzTimeZonePrivate::systemTimeZoneId() const
     return ianaId;
 }
 
+bool QTzTimeZonePrivate::isTimeZoneIdAvailable(const QByteArray &ianaId) const
+{
+    return tzZones->contains(ianaId);
+}
+
 QList<QByteArray> QTzTimeZonePrivate::availableTimeZoneIds() const
 {
     QList<QByteArray> result = tzZones->keys();