QTzTimeZonePrivate: replace an inefficient QList with QVector (II)

The implementation-private QTzTransition type is larger than void*,
so holding them in QLists is horribly inefficient.

Fix by declaring it as a primitive types (it just contains
various integers) and holding it in QVector instead.

Also optimize parseTzTransitions() by preallocating the expected
number of transitions and streaming directly into the container,
resizing to the number of successful read items on error.

Saves roughly 0.5K in text size, too.

Change-Id: Iadec7a7b0721893e477e1778c9fb54afd6e49544
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 12 insertions, 13 deletions

diff --git a/src/corelib/tools/qtimezoneprivate_tz.cpp b/src/corelib/tools/qtimezoneprivate_tz.cpp
index 78a5ecdd1e..da1cadd3ef 100644
--- a/src/corelib/tools/qtimezoneprivate_tz.cpp
+++ b/src/corelib/tools/qtimezoneprivate_tz.cpp
@@ -119,6 +119,7 @@ struct QTzTransition {
     qint64 tz_time;     // Transition time
     quint8 tz_typeind;  // Type Index
 };
+Q_DECLARE_TYPEINFO(QTzTransition, Q_PRIMITIVE_TYPE);
 
 struct QTzType {
     int tz_gmtoff;  // UTC offset in seconds
@@ -176,27 +177,25 @@ static QTzHeader parseTzHeader(QDataStream &ds, bool *ok)
     return hdr;
 }
 
-static QList<QTzTransition> parseTzTransitions(QDataStream &ds, int tzh_timecnt, bool longTran)
+static QVector<QTzTransition> parseTzTransitions(QDataStream &ds, int tzh_timecnt, bool longTran)
 {
-    QList<QTzTransition> tranList;
+    QVector<QTzTransition> transitions(tzh_timecnt);
 
     if (longTran) {
         // Parse tzh_timecnt x 8-byte transition times
         for (int i = 0; i < tzh_timecnt && ds.status() == QDataStream::Ok; ++i) {
-            QTzTransition tran;
-            ds >> tran.tz_time;
-            if (ds.status() == QDataStream::Ok)
-                tranList.append(tran);
+            ds >> transitions[i].tz_time;
+            if (ds.status() != QDataStream::Ok)
+                transitions.resize(i);
         }
     } else {
         // Parse tzh_timecnt x 4-byte transition times
         int val;
         for (int i = 0; i < tzh_timecnt && ds.status() == QDataStream::Ok; ++i) {
-            QTzTransition tran;
             ds >> val;
-            tran.tz_time = val;
-            if (ds.status() == QDataStream::Ok)
-                tranList.append(tran);
+            transitions[i].tz_time = val;
+            if (ds.status() != QDataStream::Ok)
+                transitions.resize(i);
         }
     }
 
@@ -205,10 +204,10 @@ static QList<QTzTransition> parseTzTransitions(QDataStream &ds, int tzh_timecnt,
         quint8 typeind;
         ds >> typeind;
         if (ds.status() == QDataStream::Ok)
-            tranList[i].tz_typeind = typeind;
+            transitions[i].tz_typeind = typeind;
     }
 
-    return tranList;
+    return transitions;
 }
 
 static QList<QTzType> parseTzTypes(QDataStream &ds, int tzh_typecnt)
@@ -568,7 +567,7 @@ void QTzTimeZonePrivate::init(const QByteArray &ianaId)
     QTzHeader hdr = parseTzHeader(ds, &ok);
     if (!ok || ds.status() != QDataStream::Ok)
         return;
-    QList<QTzTransition> tranList = parseTzTransitions(ds, hdr.tzh_timecnt, false);
+    QVector<QTzTransition> tranList = parseTzTransitions(ds, hdr.tzh_timecnt, false);
     if (ds.status() != QDataStream::Ok)
         return;
     QList<QTzType> typeList = parseTzTypes(ds, hdr.tzh_typecnt);