make qreal double by default on all platforms

On modern ARM CPUs there is no speed difference between
float and double anymore, so let's rather use double for
qreal to avoid rounding and precision issues. Like this
we also get much better compatibility with our desktop
OSes.

This is not binary compatible on ARM, but the old behavior
can be restored by passing -qreal float to configure.

Change-Id: I2a4b61e19a3dfa6b0bd76734cecf2634c97207fc
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

4 files changed, 39 insertions, 3 deletions

diff --git a/configure b/configure
index b5e375baed..4adaa77403 100755
--- a/configure
+++ b/configure
@@ -1006,6 +1006,7 @@ QPA_PLATFORM_GUARD=yes
 CFG_CXX11=auto
 CFG_DIRECTWRITE=no
 CFG_WERROR=auto
+CFG_QREAL=double
 OPT_MAC_SDK=
 
 # initalize variables used for installation
@@ -1168,6 +1169,7 @@ while [ "$#" -gt 0 ]; do
     -mysql_config| \
     -qpa| \
     -qconfig| \
+    -qreal| \
     -android-sdk| \
     -android-ndk| \
     -android-ndk-platform| \
@@ -1419,6 +1421,9 @@ while [ "$#" -gt 0 ]; do
     qconfig)
         CFG_QCONFIG="$VAL"
         ;;
+    qreal)
+        CFG_QREAL="$VAL"
+        ;;
     sysroot)
         CFG_SYSROOT="$VAL"
         ;;
@@ -3699,6 +3704,9 @@ Additional options:
     -qconfig local ...... Use src/corelib/global/qconfig-local.h rather than the
                           default ($CFG_QCONFIG).
 
+    -qreal [double|float] typedef qreal to the specified type. The default is double.
+                          Note that changing this flag affects binary compatibility.
+
     -no-opengl .......... Do not support OpenGL.
     -opengl <api> ....... Enable OpenGL support
                           With no parameter, this will attempt to auto-detect
@@ -6356,6 +6364,10 @@ if [ "$CFG_LARGEFILE" = "yes" ] && [ "$XPLATFORM_MINGW" != "yes" ]; then
     echo "#define QT_LARGEFILE_SUPPORT 64" >>"$outpath/src/corelib/global/qconfig.h.new"
 fi
 
+if [ "$CFG_QREAL" != double ]; then
+    echo "#define QT_COORD_TYPE $CFG_QREAL" >>"$outpath/src/corelib/global/qconfig.h.new"
+fi
+
 if [ "$CFG_FRAMEWORK" = "yes" ]; then
     echo "#define QT_MAC_FRAMEWORK_BUILD" >>"$outpath/src/corelib/global/qconfig.h.new"
 fi
@@ -6960,6 +6972,10 @@ if [ "$ORIG_CFG_XKBCOMMON" != qt ] && [ "$CFG_XKBCOMMON" = qt ]; then
     echo "NOTE: libxkbcommon 0.2.0 (or higher) not found on the system, will use "
     echo "the bundled version from 3rd party directory."
 fi
+if [ "$CFG_QREAL" = double ] && [ "$CFG_ARCH" = arm ]; then
+    echo "NOTE: Qt is using double for qreal on this system. This is binary incompatible against Qt 5.1."
+    echo "Configure with '-qreal float' to create a build that is binary compatible with 5.1."
+fi
 
 exec 1>&3 3>&- # restore stdout
 cat $outpath/config.summary # display config feedback to user
diff --git a/dist/changes-5.2.0 b/dist/changes-5.2.0
index 1eda87b553..c0db0f28f9 100644
--- a/dist/changes-5.2.0
+++ b/dist/changes-5.2.0
@@ -16,9 +16,20 @@ Each of these identifiers can be entered in the bug tracker to obtain more
 information about a particular change.
 
 ****************************************************************************
+*                     Architecture Specific Changes                        *
+****************************************************************************
+
+Qt is now compiled with qreal typedef'ed to double on all platforms. qreal
+was a float on ARM chipsets before. This guarantees more consistent behavior
+between all platforms Qt supports, but is binary incompatible to Qt 5.1
+on ARM. The old behavior can be restored by passing -qreal float to
+configure.
+
+****************************************************************************
 *                          Library                                         *
 ****************************************************************************
 
+
 QtWidgets
 ---------
 
diff --git a/src/corelib/global/qglobal.h b/src/corelib/global/qglobal.h
index 0fd9bab979..5bb675728a 100644
--- a/src/corelib/global/qglobal.h
+++ b/src/corelib/global/qglobal.h
@@ -213,11 +213,8 @@ typedef unsigned int uint;
 typedef unsigned long ulong;
 QT_END_INCLUDE_NAMESPACE
 
-// This logic must match the one in qmetatype.h
 #if defined(QT_COORD_TYPE)
 typedef QT_COORD_TYPE qreal;
-#elif defined(QT_NO_FPU) || defined(Q_PROCESSOR_ARM) || defined(Q_OS_WINCE)
-typedef float qreal;
 #else
 typedef double qreal;
 #endif
diff --git a/tools/configure/configureapp.cpp b/tools/configure/configureapp.cpp
index 5d4ce84941..4c323a3540 100644
--- a/tools/configure/configureapp.cpp
+++ b/tools/configure/configureapp.cpp
@@ -196,6 +196,7 @@ Configure::Configure(int& argc, char** argv)
     dictionary[ "SLOG2" ]           = "no";
     dictionary[ "SYSTEM_PROXIES" ]  = "no";
     dictionary[ "WERROR" ]          = "auto";
+    dictionary[ "QREAL" ]           = "double";
 
     //Only used when cross compiling.
     dictionary[ "QT_INSTALL_SETTINGS" ] = "/etc/xdg";
@@ -418,6 +419,12 @@ void Configure::parseCmdLine()
                 break;
             dictionary[ "QCONFIG" ] = configCmdLine.at(i);
         }
+        else if (configCmdLine.at(i) == "-qreal") {
+            ++i;
+            if (i == argCount)
+                break;
+            dictionary[ "QREAL" ] = configCmdLine.at(i);
+        }
 
         else if (configCmdLine.at(i) == "-release") {
             dictionary[ "BUILD" ] = "release";
@@ -1876,6 +1883,9 @@ bool Configure::displayHelp()
         desc("PROCESS", "full", "-fully-process",       "Generate Makefiles/Project files for the entire Qt\ntree.");
         desc("PROCESS", "no", "-dont-process",          "Do not generate Makefiles/Project files.\n");
 
+        desc(                  "-qreal [double|float]", "typedef qreal to the specified type. The default is double.\n"
+                                                        "Note that changing this flag affects binary compatibility.\n");
+
         desc("RTTI", "no",      "-no-rtti",             "Do not compile runtime type information.");
         desc("RTTI", "yes",     "-rtti",                "Compile runtime type information.");
         desc("STRIP", "no",     "-no-strip",            "Do not strip libraries and executables of debug info when installing.");
@@ -3298,6 +3308,8 @@ void Configure::generateConfigfiles()
         if (dictionary[ "NEON" ] == "yes")
             tmpStream << "#define QT_COMPILER_SUPPORTS_NEON" << endl;
 
+        if (dictionary["QREAL"] != "double")
+            tmpStream << "#define QT_COORD_TYPE " << dictionary["QREAL"] << endl;
 
         tmpStream << endl << "// Compile time features" << endl;