From 4aa0eab263917ee8dc104be3d858f53d8033662f Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Sat, 10 Feb 2024 13:02:03 -0800
Subject: [PATCH] QDataStream: inline floatingPointPrecision()

There is a 2-byte padding in all architectures between the noswap member
and byteorder, because the latter requires a 32-bit alignment. So we can
use this space to store this little-used field and avoid one more reason
for QDataStreamPrivate.

Now:
  class QScopedPointer<QDataStreamPrivate> d;      /*     0     8 */
  class QIODevice *          dev;                  /*     8     8 */
  bool                       owndev;               /*    16     1 */
  bool                       noswap;               /*    17     1 */
  quint8                     fpPrecision;          /*    18     1 */
  /* XXX 1 byte hole, try to pack */
  enum ByteOrder             byteorder;            /*    20     4 */
  int                        ver;                  /*    24     4 */
  enum Status                q_status;             /*    28     4 */
  /* size: 32, cachelines: 1, members: 9 */

Change-Id: I50e2158aeade4256ad1dfffd17b29c2c5db02c12
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
---
 src/corelib/serialization/qdatastream.cpp | 10 +++-------
 src/corelib/serialization/qdatastream.h   |  7 +++++++
 src/corelib/serialization/qdatastream_p.h |  6 +-----
 3 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/src/corelib/serialization/qdatastream.cpp b/src/corelib/serialization/qdatastream.cpp
index 826eecab87d..5be4e734c67 100644
--- a/src/corelib/serialization/qdatastream.cpp
+++ b/src/corelib/serialization/qdatastream.cpp
@@ -406,16 +406,14 @@ bool QDataStream::atEnd() const
 }
 
 /*!
+    \fn QDataStream::FloatingPointPrecision QDataStream::floatingPointPrecision() const
+
     Returns the floating point precision of the data stream.
 
     \since 4.6
 
     \sa FloatingPointPrecision, setFloatingPointPrecision()
 */
-QDataStream::FloatingPointPrecision QDataStream::floatingPointPrecision() const
-{
-    return d ? d->floatingPointPrecision : QDataStream::DoublePrecision;
-}
 
 /*!
     Sets the floating point precision of the data stream to \a precision. If the floating point precision is
@@ -439,9 +437,7 @@ QDataStream::FloatingPointPrecision QDataStream::floatingPointPrecision() const
 */
 void QDataStream::setFloatingPointPrecision(QDataStream::FloatingPointPrecision precision)
 {
-    if (!d)
-        d.reset(new QDataStreamPrivate());
-    d->floatingPointPrecision = precision;
+    fpPrecision = precision;
 }
 
 /*!
diff --git a/src/corelib/serialization/qdatastream.h b/src/corelib/serialization/qdatastream.h
index efcc23e49a8..b4be27f4742 100644
--- a/src/corelib/serialization/qdatastream.h
+++ b/src/corelib/serialization/qdatastream.h
@@ -127,6 +127,7 @@ public:
     void setStatus(Status status);
     void resetStatus();
 
+    QT_CORE_INLINE_SINCE(6, 8)
     FloatingPointPrecision floatingPointPrecision() const;
     void setFloatingPointPrecision(FloatingPointPrecision precision);
 
@@ -218,6 +219,7 @@ private:
     QIODevice *dev;
     bool owndev;
     bool noswap;
+    quint8 fpPrecision = QDataStream::DoublePrecision;
     ByteOrder byteorder;
     int ver;
     Status q_status;
@@ -426,6 +428,11 @@ QDataStream::Status QDataStream::status() const
 {
     return q_status;
 }
+
+QDataStream::FloatingPointPrecision QDataStream::floatingPointPrecision() const
+{
+    return FloatingPointPrecision(fpPrecision);
+}
 #endif // INLINE_SINCE 6.8
 
 inline QDataStream::ByteOrder QDataStream::byteOrder() const
diff --git a/src/corelib/serialization/qdatastream_p.h b/src/corelib/serialization/qdatastream_p.h
index 0e7ebb5750a..4600fa64d02 100644
--- a/src/corelib/serialization/qdatastream_p.h
+++ b/src/corelib/serialization/qdatastream_p.h
@@ -24,11 +24,7 @@ QT_BEGIN_NAMESPACE
 class QDataStreamPrivate
 {
 public:
-    QDataStreamPrivate() : floatingPointPrecision(QDataStream::DoublePrecision),
-        transactionDepth(0) { }
-
-    QDataStream::FloatingPointPrecision floatingPointPrecision;
-    int transactionDepth;
+    int transactionDepth = 0;
 };
 #endif