From 81a45e1f13fdf56129aed952a6e3479e16c14a2c Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@kdab.com>
Date: Sat, 26 Jul 2014 01:43:18 +0200
Subject: QTimeZone: don't use QSet, use sorted QList

QSet, as a node-based container, requires one memory allocation per element
inserted. QList, as a contiguous-memory container (at least in the case of
a QByteArray payload), requires one memory allocation per container.

The higher lookup speed might still speak for using QSet, but there are only
two uses of the sets:

1. Checking for existence (or lack thereof) of timezone names.
   For this, first generating a container full of data just to check for
   existence of one item of data is extremely wasteful. The QTZPrivate
   API should be extended to allow said lookup to be performed on the
   native data store instead.

That leaves

2. Returning a sorted(!) list(!) from the public QTimeZone API.
   There is no reason why, during the construction of those sorted
   lists, the data should be held in a set. Instead, the well-known
   technique of first cramming everything into a result container,
   which is subsequently sorted and has its duplicates removed,
   can be used here.

Saves more than 8K of text size on AMD64 stripped release builds.

Change-Id: I71c2298e94e02d55b0c9fb6f7ebeaed79a1fe2db
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/tools/qtimezoneprivate_icu.cpp | 37 +++++++++++++++++-------------
 1 file changed, 21 insertions(+), 16 deletions(-)

(limited to 'src/corelib/tools/qtimezoneprivate_icu.cpp')

diff --git a/src/corelib/tools/qtimezoneprivate_icu.cpp b/src/corelib/tools/qtimezoneprivate_icu.cpp
index 3ab42661c0..dd57464a72 100644
--- a/src/corelib/tools/qtimezoneprivate_icu.cpp
+++ b/src/corelib/tools/qtimezoneprivate_icu.cpp
@@ -37,6 +37,9 @@
 #include <unicode/ucal.h>
 
 #include <qdebug.h>
+#include <qlist.h>
+
+#include <algorithm>
 
 QT_BEGIN_NAMESPACE
 
@@ -234,19 +237,21 @@ static QTimeZonePrivate::Data ucalTimeZoneTransition(UCalendar *m_ucal,
 #endif // U_ICU_VERSION_SHORT
 
 // Convert a uenum to a QList<QByteArray>
-static QSet<QByteArray> uenumToIdSet(UEnumeration *uenum)
+static QList<QByteArray> uenumToIdList(UEnumeration *uenum)
 {
-    QSet<QByteArray> set;
+    QList<QByteArray> list;
     int32_t size = 0;
     UErrorCode status = U_ZERO_ERROR;
     // TODO Perhaps use uenum_unext instead?
     QByteArray result = uenum_next(uenum, &size, &status);
     while (U_SUCCESS(status) && !result.isEmpty()) {
-        set << result;
+        list << result;
         status = U_ZERO_ERROR;
         result = uenum_next(uenum, &size, &status);
     }
-    return set;
+    std::sort(list.begin(), list.end());
+    list.erase(std::unique(list.begin(), list.end()), list.end());
+    return list;
 }
 
 // Qt wrapper around ucal_getDSTSavings()
@@ -453,41 +458,41 @@ QByteArray QIcuTimeZonePrivate::systemTimeZoneId() const
     return ucalDefaultTimeZoneId();
 }
 
-QSet<QByteArray> QIcuTimeZonePrivate::availableTimeZoneIds() const
+QList<QByteArray> QIcuTimeZonePrivate::availableTimeZoneIds() const
 {
     UErrorCode status = U_ZERO_ERROR;
     UEnumeration *uenum = ucal_openTimeZones(&status);
-    QSet<QByteArray> set;
+    QList<QByteArray> result;
     if (U_SUCCESS(status))
-        set = uenumToIdSet(uenum);
+        result = uenumToIdList(uenum);
     uenum_close(uenum);
-    return set;
+    return result;
 }
 
-QSet<QByteArray> QIcuTimeZonePrivate::availableTimeZoneIds(QLocale::Country country) const
+QList<QByteArray> QIcuTimeZonePrivate::availableTimeZoneIds(QLocale::Country country) const
 {
     QByteArray regionCode = QLocalePrivate::countryToCode(country).toUtf8();
     UErrorCode status = U_ZERO_ERROR;
     UEnumeration *uenum = ucal_openCountryTimeZones(regionCode, &status);
-    QSet<QByteArray> set;
+    QList<QByteArray> result;
     if (U_SUCCESS(status))
-        set = uenumToIdSet(uenum);
+        result = uenumToIdList(uenum);
     uenum_close(uenum);
-    return set;
+    return result;
 }
 
-QSet<QByteArray> QIcuTimeZonePrivate::availableTimeZoneIds(int offsetFromUtc) const
+QList<QByteArray> QIcuTimeZonePrivate::availableTimeZoneIds(int offsetFromUtc) const
 {
 // TODO Available directly in C++ api but not C api, from 4.8 onwards new filter method works
 #if U_ICU_VERSION_MAJOR_NUM >= 49 || (U_ICU_VERSION_MAJOR_NUM == 4 && U_ICU_VERSION_MINOR_NUM == 8)
     UErrorCode status = U_ZERO_ERROR;
     UEnumeration *uenum = ucal_openTimeZoneIDEnumeration(UCAL_ZONE_TYPE_ANY, 0,
                                                          &offsetFromUtc, &status);
-    QSet<QByteArray> set;
+    QList<QByteArray> result;
     if (U_SUCCESS(status))
-        set = uenumToIdSet(uenum);
+        result = uenumToIdList(uenum);
     uenum_close(uenum);
-    return set;
+    return result;
 #else
     return QTimeZonePrivate::availableTimeZoneIds(offsetFromUtc);
 #endif
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