QCborValue: store US-ASCII strings as 8-bit

They're easy to convert back to UTF-16, their length is the same, they
occupy half the memory and they're easy to encode into CBOR (no
transformation necessary).

The code was copied from QJsonPrivate::Latin1String::operator=().

Change-Id: I56b444f9d6274221a3b7fffd150c52bcb6c97f37
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/src/corelib/serialization/qcborvalue_p.h b/src/corelib/serialization/qcborvalue_p.h
index 861b91eec0..c80abd68f5 100644
--- a/src/corelib/serialization/qcborvalue_p.h
+++ b/src/corelib/serialization/qcborvalue_p.h
@@ -153,7 +153,8 @@ public:
         char *ptr = data.begin() + offset;
         auto b = new (ptr) QtCbor::ByteData;
         b->len = len;
-        memcpy(b->byte(), block, len);
+        if (block)
+            memcpy(b->byte(), block, len);
 
         return offset;
     }
@@ -239,10 +240,14 @@ public:
         appendByteData(s.latin1(), s.size(), QCborValue::String,
                        QtCbor::Element::StringIsAscii);
     }
+    void appendAsciiString(const QString &s);
     void append(const QString &s)
     {
-        appendByteData(reinterpret_cast<const char *>(s.constData()), s.size() * 2,
-                       QCborValue::String, QtCbor::Element::StringIsUtf16);
+        if (QtPrivate::isAscii(s))
+            appendAsciiString(s);
+        else
+            appendByteData(reinterpret_cast<const char *>(s.constData()), s.size() * 2,
+                           QCborValue::String, QtCbor::Element::StringIsUtf16);
     }
     void append(const QCborValue &v)
     {