From 4ff09cdd47a1f21321a56017743401a7c6b91ad3 Mon Sep 17 00:00:00 2001
From: Lars Knoll <lars.knoll@qt.io>
Date: Tue, 5 May 2020 15:45:47 +0200
Subject: [PATCH] Optimize appending to an existing string

Optimize the common pattern of "str += decode(data);"
and "bytearray += encode(string);"

Change-Id: I1da621fa1ad400f23c9718ecf8ae64c00d9d459c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/text/qstringconverter.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/src/corelib/text/qstringconverter.h b/src/corelib/text/qstringconverter.h
index 7443173df6..989773e113 100644
--- a/src/corelib/text/qstringconverter.h
+++ b/src/corelib/text/qstringconverter.h
@@ -327,6 +327,28 @@ struct QConcatenable<QStringEncoder::DecodedData<T>>
         out = s.decoder->decodeIntoBuffer(out, s.data.data(), s.data.length());
     }
 };
+
+template <typename T>
+QString &operator+=(QString &a, const QStringDecoder::EncodedData<T> &b)
+{
+    qsizetype len = a.size() + QConcatenable<QStringDecoder::EncodedData<T>>::size(b);
+    a.reserve(len);
+    QChar *it = a.data() + a.size();
+    QConcatenable<QStringDecoder::EncodedData<T>>::appendTo(b, it);
+    a.resize(qsizetype(it - a.constData())); //may be smaller than len
+    return a;
+}
+
+template <typename T>
+QByteArray &operator+=(QByteArray &a, const QStringEncoder::DecodedData<T> &b)
+{
+    qsizetype len = a.size() + QConcatenable<QStringEncoder::DecodedData<T>>::size(b);
+    a.reserve(len);
+    char *it = a.data() + a.size();
+    QConcatenable<QStringEncoder::DecodedData<T>>::appendTo(b, it);
+    a.resize(qsizetype(it - a.constData())); //may be smaller than len
+    return a;
+}
 #endif
 
 QT_END_NAMESPACE