QTextStream: stream QStrings without modifying the user content

QTextStream::operator<< calls QTextStreamPrivate::putString, which was
taking a copy of the user's string and modifying it depending on
padding. That is not necessary, since we're only talking about
padding. Instead, calculate the left and right paddings. For the case of
"accounting padding", we move the sign (if any) to the beginning of the
left padding and skip it in the data.

The one side-effect I can think of is that the stream could flush in the
middle of the writing operation.

The debugging section had to be removed because it doesn't make sense
anymore.

Change-Id: I57fdbf98ec6f054f4e085f2e465de3dcbb6225ce
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

src/corelib/io/qtextstream.cpp

@@ -812,13 +812,13 @@ inline void QTextStreamPrivate::restoreToSavedConverterState()
 /*!
     \internal
 */
-inline void QTextStreamPrivate::write(const QString &data)
+inline void QTextStreamPrivate::write(const QChar *data, int len)
 {
     if (string) {
         // ### What about seek()??
-        string->append(data);
+        string->append(data, len);
     } else {
-        writeBuffer += data;
+        writeBuffer.append(data, len);
         if (writeBuffer.size() > QTEXTSTREAM_BUFFERSIZE)
             flushWriteBuffer();
     }
@@ -883,7 +883,7 @@ inline void QTextStreamPrivate::ungetChar(QChar ch)
 inline void QTextStreamPrivate::putChar(QChar ch)
 {
     if (params.fieldWidth > 0)
-        putString(QString(ch));
+        putString(&ch, 1);
     else
         write(ch);
 }
@@ -891,45 +891,42 @@ inline void QTextStreamPrivate::putChar(QChar ch)
 /*!
     \internal
 */
-inline void QTextStreamPrivate::putString(const QString &s, bool number)
+inline void QTextStreamPrivate::putString(const QChar *data, int len, bool number)
 {
-    QString tmp = s;
+    QString pad;
+    int padLeft = 0, padRight = 0;
 
     // handle padding
-    int padSize = params.fieldWidth - s.size();
+    int padSize = params.fieldWidth - len;
     if (padSize > 0) {
-        QString pad(padSize, params.padChar);
+        pad = QString(padSize, params.padChar);
         switch (params.fieldAlignment) {
         case QTextStream::AlignLeft:
-            tmp.append(pad);
+            padRight = padSize;
             break;
         case QTextStream::AlignRight:
         case QTextStream::AlignAccountingStyle:
-            tmp.prepend(pad);
+            padLeft = padSize;
             if (params.fieldAlignment == QTextStream::AlignAccountingStyle && number) {
-                const QChar sign = s.size() > 0 ? s.at(0) : QChar();
+                const QChar sign = len > 0 ? data[0] : QChar();
                 if (sign == locale.negativeSign() || sign == locale.positiveSign()) {
-                    QChar *data = tmp.data();
-                    data[padSize] = tmp.at(0);
-                    data[0] = sign;
+                    // write the sign before the padding, then skip it later
+                    write(&sign, 1);
+                    ++data;
+                    --len;
                 }
-           }
+            }
             break;
         case QTextStream::AlignCenter:
-            tmp.prepend(QString(padSize/2, params.padChar));
-            tmp.append(QString(padSize - padSize/2, params.padChar));
+            padLeft = padSize/2;
+            padRight = padSize - padSize/2;
             break;
         }
     }
 
-#if defined (QTEXTSTREAM_DEBUG)
-    QByteArray a = s.toUtf8();
-    QByteArray b = tmp.toUtf8();
-    qDebug("QTextStreamPrivate::putString(\"%s\") calls write(\"%s\")",
-           qt_prettyDebug(a.constData(), a.size(), qMax(16, a.size())).constData(),
-           qt_prettyDebug(b.constData(), b.size(), qMax(16, b.size())).constData());
-#endif
-    write(tmp);
+    write(pad.constData(), padLeft);
+    write(data, len);
+    write(pad.constData(), padRight);
 }
 
 /*!

src/corelib/io/qtextstream_p.h

@@ -165,9 +165,11 @@ public:
     NumberParsingStatus getNumber(qulonglong *l);
     bool getReal(double *f);
 
-    inline void write(const QString &data);
+    inline void write(const QString &data) { write(data.begin(), data.length()); }
     inline void write(QChar ch);
-    inline void putString(const QString &ch, bool number = false);
+    void write(const QChar *data, int len);
+    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);
     inline void putChar(QChar ch);
     void putNumber(qulonglong number, bool negative);