QTextStream: optimize streaming of QLatin1String and const char*

Instead of converting the QLatin1String to a QString at the first
opportunity, keep it around until it is appended to one of the
internal QStrings in write().

Avoids a memory allocation per QLatin1String / const char* streamed.

Change-Id: Id973a9b743e5a6696defbc4ef4ed2db1ef54e9cc
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qtextstream.cpp

@@ -844,6 +844,21 @@ inline void QTextStreamPrivate::write(QChar ch)
     }
 }
 
+/*!
+    \internal
+*/
+void QTextStreamPrivate::write(QLatin1String data)
+{
+    if (string) {
+        // ### What about seek()??
+        string->append(data);
+    } else {
+        writeBuffer += data;
+        if (writeBuffer.size() > QTEXTSTREAM_BUFFERSIZE)
+            flushWriteBuffer();
+    }
+}
+
 /*!
     \internal
 */
@@ -958,6 +973,34 @@ void QTextStreamPrivate::putString(const QChar *data, int len, bool number)
     }
 }
 
+/*!
+    \internal
+*/
+void QTextStreamPrivate::putString(QLatin1String data, bool number)
+{
+    if (Q_UNLIKELY(params.fieldWidth > data.size())) {
+
+        // handle padding
+
+        const PaddingResult pad = padding(data.size());
+
+        if (params.fieldAlignment == QTextStream::AlignAccountingStyle && number) {
+            const QChar sign = data.size() > 0 ? QLatin1Char(*data.data()) : QChar();
+            if (sign == locale.negativeSign() || sign == locale.positiveSign()) {
+                // write the sign before the padding, then skip it later
+                write(&sign, 1);
+                data = QLatin1String(data.data() + 1, data.size() - 1);
+            }
+        }
+
+        write(pad.padding.constData(), pad.left);
+        write(data);
+        write(pad.padding.constData(), pad.right);
+    } else {
+        write(data);
+    }
+}
+
 /*!
     Constructs a QTextStream. Before you can use it for reading or
     writing, you must assign a device or a string.
@@ -2529,14 +2572,13 @@ QTextStream &QTextStream::operator<<(const QString &string)
     \overload
 
     Writes \a string to the stream, and returns a reference to the
-    QTextStream. The contents of \a string are converted with the
-    QString constructor that takes a QLatin1String as argument.
+    QTextStream.
 */
 QTextStream &QTextStream::operator<<(QLatin1String string)
 {
     Q_D(QTextStream);
     CHECK_VALID_STREAM(*this);
-    d->putString(QString(string));
+    d->putString(string);
     return *this;
 }
 

src/corelib/io/qtextstream_p.h

@@ -168,15 +168,17 @@ public:
     inline void write(const QString &data) { write(data.begin(), data.length()); }
     inline void write(QChar ch);
     void write(const QChar *data, int len);
+    void write(QLatin1String data);
     inline void putString(const QString &ch, bool number = false) { putString(ch.constData(), ch.length(), number); }
     void putString(const QChar *data, int len, bool number = false);
+    void putString(QLatin1String data, bool number = false);
     inline void putChar(QChar ch);
     void putNumber(qulonglong number, bool negative);
 
     struct PaddingResult {
         enum { PreallocatedPadding = 80 }; // typical line length
 
-        int right, left;
+        int left, right;
         QVarLengthArray<QChar, PreallocatedPadding> padding;
     };
     PaddingResult padding(int len) const;