Boost performance of QChar::isLetter

Make it inline; add fast checks for ascii letters;
add fallback function that uses the fastcall calling
convention.

On ia32, this change makes isLetter ~370x faster for
ascii letters, ~250x faster for non-letter ascii
characters, and ~1.5x faster for non-ascii characters.

Note that this change is NOT binary compatible.

Also add an autotest with expected results from
before the optimization, to ensure that the
behavior is the same.

Change-Id: I06f8d3d43114537cee5567e670898cef6494c20a
Reviewed-on: http://codereview.qt-project.org/4903
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>

src/corelib/tools/qchar.cpp

@@ -556,17 +556,24 @@ bool QChar::isPunct() const
 }
 
 /*!
+    \fn bool QChar::isLetter() const
+
     Returns true if the character is a letter (Letter_* categories);
     otherwise returns false.
 */
-bool QChar::isLetter() const
+
+/*!
+    \internal
+    \overload
+*/
+bool QChar::isLetter(ushort ucs2)
 {
     const int test = FLAG(Letter_Uppercase) |
                      FLAG(Letter_Lowercase) |
                      FLAG(Letter_Titlecase) |
                      FLAG(Letter_Modifier) |
                      FLAG(Letter_Other);
-    return FLAG(qGetProp(ucs)->category) & test;
+    return FLAG(qGetProp(ucs2)->category) & test;
 }
 
 /*!

src/corelib/tools/qchar.h

@@ -234,7 +234,11 @@ public:
     bool isPunct() const;
     bool isSpace() const;
     bool isMark() const;
-    bool isLetter() const;
+    inline bool isLetter() const {
+        return (ucs >= 'a' && ucs <= 'z')
+                || (ucs <= 'Z' && ucs >= 'A')
+                || (ucs > 127 && isLetter(ucs));
+    }
     bool isNumber() const;
     bool isLetterOrNumber() const;
     inline bool isDigit() const
@@ -317,6 +321,7 @@ public:
 
 private:
     static bool QT_FASTCALL isDigit(ushort ucs2);
+    static bool QT_FASTCALL isLetter(ushort ucs2);
 
 #ifdef QT_NO_CAST_FROM_ASCII
     QChar(char c);

tests/auto/corelib/tools/qchar/tst_qchar.cpp

@@ -75,6 +75,8 @@ private slots:
     void toCaseFolded();
     void isDigit_data();
     void isDigit();
+    void isLetter_data();
+    void isLetter();
     void isPrint();
     void isUpper();
     void isLower();
@@ -244,6 +246,33 @@ void tst_QChar::isDigit()
     QCOMPARE(QChar(ucs).isDigit(), expected);
 }
 
+static bool isExpectedLetter(ushort ucs)
+{
+    return (ucs >= 'a' && ucs <= 'z') || (ucs >= 'A' && ucs <= 'Z')
+            || ucs == 0xAA || ucs == 0xB5 || ucs == 0xBA
+            || (ucs >= 0xC0 && ucs <= 0xD6)
+            || (ucs >= 0xD8 && ucs <= 0xF6)
+            || (ucs >= 0xF8 && ucs <= 0xFF);
+}
+
+void tst_QChar::isLetter_data()
+{
+    QTest::addColumn<ushort>("ucs");
+    QTest::addColumn<bool>("expected");
+
+    for (ushort ucs = 0; ucs < 256; ++ucs) {
+        QString tag = QString::fromLatin1("0x%0").arg(QString::number(ucs, 16));
+        QTest::newRow(tag.toLatin1()) << ucs << isExpectedLetter(ucs);
+    }
+}
+
+void tst_QChar::isLetter()
+{
+    QFETCH(ushort, ucs);
+    QFETCH(bool, expected);
+    QCOMPARE(QChar(ucs).isLetter(), expected);
+}
+
 void tst_QChar::isPrint()
 {
     QVERIFY(QChar('A').isPrint());