Port QLocalePrivate::*ToCode() to QLatin1String

The returned data is in US-ASCII (or else Latin-1), and resides in
consecutive memory. We can therefore return it in a QLatin1String,
which, however, will in general not be NUL-terminated.

Many users use the return value as part of a QStringBuilder
expression, and those which are not are not pessimized further by
this change.

The caller in qtimezoneprivate_icu looks as if it could simply zero
-terminate the return value and use it as-is, as opposed to
converting to UTF-8, but I left the code equivalent to the original
just the same.

Change-Id: I0e628af8c1320fcff8d0aacf160e859681d2b85a
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

3 files changed, 19 insertions, 32 deletions

diff --git a/src/corelib/tools/qlocale.cpp b/src/corelib/tools/qlocale.cpp
index 59952bd107..35aa0df0ef 100644
--- a/src/corelib/tools/qlocale.cpp
+++ b/src/corelib/tools/qlocale.cpp
@@ -167,48 +167,35 @@ QLocale::Country QLocalePrivate::codeToCountry(const QChar *code, int len) Q_DEC
     return QLocale::AnyCountry;
 }
 
-QString QLocalePrivate::languageToCode(QLocale::Language language)
+QLatin1String QLocalePrivate::languageToCode(QLocale::Language language)
 {
     if (language == QLocale::AnyLanguage)
-        return QString();
+        return QLatin1String();
     if (language == QLocale::C)
         return QLatin1String("C");
 
     const unsigned char *c = language_code_list + 3*(uint(language));
 
-    QString code(c[2] == 0 ? 2 : 3, Qt::Uninitialized);
-
-    code[0] = ushort(c[0]);
-    code[1] = ushort(c[1]);
-    if (c[2] != 0)
-        code[2] = ushort(c[2]);
+    return QLatin1String(reinterpret_cast<const char*>(c), c[2] == 0 ? 2 : 3);
 
-    return code;
 }
 
-QString QLocalePrivate::scriptToCode(QLocale::Script script)
+QLatin1String QLocalePrivate::scriptToCode(QLocale::Script script)
 {
     if (script == QLocale::AnyScript || script > QLocale::LastScript)
-        return QString();
+        return QLatin1String();
     const unsigned char *c = script_code_list + 4*(uint(script));
-    return QString::fromLatin1((const char *)c, 4);
+    return QLatin1String(reinterpret_cast<const char *>(c), 4);
 }
 
-QString QLocalePrivate::countryToCode(QLocale::Country country)
+QLatin1String QLocalePrivate::countryToCode(QLocale::Country country)
 {
     if (country == QLocale::AnyCountry)
-        return QString();
+        return QLatin1String();
 
     const unsigned char *c = country_code_list + 3*(uint(country));
 
-    QString code(c[2] == 0 ? 2 : 3, Qt::Uninitialized);
-
-    code[0] = ushort(c[0]);
-    code[1] = ushort(c[1]);
-    if (c[2] != 0)
-        code[2] = ushort(c[2]);
-
-    return code;
+    return QLatin1String(reinterpret_cast<const char*>(c), c[2] == 0 ? 2 : 3);
 }
 
 // http://www.unicode.org/reports/tr35/#Likely_Subtags
diff --git a/src/corelib/tools/qlocale_p.h b/src/corelib/tools/qlocale_p.h
index f7adb021b6..1c6e3e850b 100644
--- a/src/corelib/tools/qlocale_p.h
+++ b/src/corelib/tools/qlocale_p.h
@@ -349,14 +349,13 @@ public:
 
     QByteArray bcp47Name(char separator = '-') const;
 
-    // ### QByteArray::fromRawData would be more optimal
-    inline QString languageCode() const { return QLocalePrivate::languageToCode(QLocale::Language(m_data->m_language_id)); }
-    inline QString scriptCode() const { return QLocalePrivate::scriptToCode(QLocale::Script(m_data->m_script_id)); }
-    inline QString countryCode() const { return QLocalePrivate::countryToCode(QLocale::Country(m_data->m_country_id)); }
-
-    static QString languageToCode(QLocale::Language language);
-    static QString scriptToCode(QLocale::Script script);
-    static QString countryToCode(QLocale::Country country);
+    inline QLatin1String languageCode() const { return QLocalePrivate::languageToCode(QLocale::Language(m_data->m_language_id)); }
+    inline QLatin1String scriptCode() const { return QLocalePrivate::scriptToCode(QLocale::Script(m_data->m_script_id)); }
+    inline QLatin1String countryCode() const { return QLocalePrivate::countryToCode(QLocale::Country(m_data->m_country_id)); }
+
+    static QLatin1String languageToCode(QLocale::Language language);
+    static QLatin1String scriptToCode(QLocale::Script script);
+    static QLatin1String countryToCode(QLocale::Country country);
     static QLocale::Language codeToLanguage(const QChar *code, int len) Q_DECL_NOTHROW;
     static QLocale::Language codeToLanguage(const QString &code) Q_DECL_NOTHROW { return codeToLanguage(code.data(), code.size()); }
     static QLocale::Language codeToLanguage(const QStringRef &code) Q_DECL_NOTHROW { return codeToLanguage(code.data(), code.size()); }
diff --git a/src/corelib/tools/qtimezoneprivate_icu.cpp b/src/corelib/tools/qtimezoneprivate_icu.cpp
index 887486f567..a07b2593b9 100644
--- a/src/corelib/tools/qtimezoneprivate_icu.cpp
+++ b/src/corelib/tools/qtimezoneprivate_icu.cpp
@@ -477,9 +477,10 @@ QList<QByteArray> QIcuTimeZonePrivate::availableTimeZoneIds() const
 
 QList<QByteArray> QIcuTimeZonePrivate::availableTimeZoneIds(QLocale::Country country) const
 {
-    QByteArray regionCode = QLocalePrivate::countryToCode(country).toUtf8();
+    const QLatin1String regionCode = QLocalePrivate::countryToCode(country);
+    const QByteArray regionCodeUtf8 = QString(regionCode).toUtf8();
     UErrorCode status = U_ZERO_ERROR;
-    UEnumeration *uenum = ucal_openCountryTimeZones(regionCode, &status);
+    UEnumeration *uenum = ucal_openCountryTimeZones(regionCodeUtf8.data(), &status);
     QList<QByteArray> result;
     if (U_SUCCESS(status))
         result = uenumToIdList(uenum);