Interpret precision == -128 as "shortest" double conversion

Also use this for converting doubles with QVariant. We generally want
exact results there, rather than adding rounding errors whenever we
convert.

[ChangeLog][QtCore][QLocale] Added special value for double conversion
precision to get shortest accurate representation.

Change-Id: I905b8a103f39adf31d24b6ce2c8a283cf271b597
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

4 files changed, 108 insertions, 35 deletions

diff --git a/tests/auto/corelib/kernel/qvariant/qvariant.pro b/tests/auto/corelib/kernel/qvariant/qvariant.pro
index a2dda809ad..33e8b6e2ad 100644
--- a/tests/auto/corelib/kernel/qvariant/qvariant.pro
+++ b/tests/auto/corelib/kernel/qvariant/qvariant.pro
@@ -1,8 +1,11 @@
 CONFIG += testcase
 TARGET = tst_qvariant
-QT = core testlib
+QT = core-private testlib
 INCLUDEPATH += $$PWD/../../../other/qvariant_common
 SOURCES = tst_qvariant.cpp
 RESOURCES += qvariant.qrc
 DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0
 contains(QT_CONFIG, c++11): CONFIG += c++11
+!contains(QT_CONFIG, doubleconversion):!contains(QT_CONFIG, system-doubleconversion) {
+    DEFINES += QT_NO_DOUBLECONVERSION
+}
diff --git a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
index de53ab1fa3..0c4efcd0c2 100644
--- a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
+++ b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
@@ -56,6 +56,7 @@
 #include <QBuffer>
 #include "qnumeric.h"
 
+#include <private/qlocale_p.h>
 #include "tst_qvariant_common.h"
 
 class CustomNonQObject;
@@ -1028,7 +1029,11 @@ void tst_QVariant::toByteArray_data()
     QTest::newRow( "int" ) << QVariant( -123 ) << QByteArray( "-123" );
     QTest::newRow( "uint" ) << QVariant( (uint)123 ) << QByteArray( "123" );
     QTest::newRow( "double" ) << QVariant( 123.456 ) << QByteArray( "123.456" );
-    QTest::newRow( "float" ) << QVariant( 123.456f ) << QByteArray( "123.456001" );
+
+    // Conversion from float to double adds bits of which the double-to-string converter doesn't
+    // know they're insignificant
+    QTest::newRow( "float" ) << QVariant( 123.456f ) << QByteArray( "123.45600128173828" );
+
     QTest::newRow( "longlong" ) << QVariant( (qlonglong)34 ) << QByteArray( "34" );
     QTest::newRow( "ulonglong" ) << QVariant( (qulonglong)34 ) << QByteArray( "34" );
 }
@@ -1054,7 +1059,11 @@ void tst_QVariant::toString_data()
     QTest::newRow( "int" ) << QVariant( -123 ) << QString( "-123" );
     QTest::newRow( "uint" ) << QVariant( (uint)123 ) << QString( "123" );
     QTest::newRow( "double" ) << QVariant( 123.456 ) << QString( "123.456" );
-    QTest::newRow( "float" ) << QVariant( 123.456f ) << QString( "123.456001" );
+
+    // Conversion from float to double adds bits of which the double-to-string converter doesn't
+    // know they're insignificant
+    QTest::newRow( "float" ) << QVariant( 123.456f ) << QString( "123.45600128173828" );
+
     QTest::newRow( "bool" ) << QVariant( true ) << QString( "true" );
     QTest::newRow( "qdate" ) << QVariant( QDate( 2002, 1, 1 ) ) << QString( "2002-01-01" );
     QTest::newRow( "qtime" ) << QVariant( QTime( 12, 34, 56 ) ) << QString( "12:34:56" );
@@ -1411,12 +1420,28 @@ void tst_QVariant::operator_eq_eq_data()
     QVariant mUIntQString(QString("42"));
 
     QVariant mDouble(42.11);
+#ifdef QT_NO_DOUBLECONVERSION
+    // Without libdouble-conversion we don't get the shortest possible representation.
     QVariant mDoubleString(QByteArray("42.109999999999999"));
-    QVariant mDoubleQString(QString("42.109999999999999"));
+    QVariant mDoubleQString(QByteArray("42.109999999999999"));
+#else
+    // You cannot fool the double-to-string conversion into producing insignificant digits with
+    // libdouble-conversion. You can, of course, add insignificant digits to the string and fool
+    // the double-to-double comparison after converting the string to a double.
+    QVariant mDoubleString(QByteArray("42.11"));
+    QVariant mDoubleQString(QString("42.11"));
+#endif
 
+    // Float-to-double conversion produces insignificant extra bits.
     QVariant mFloat(42.11f);
-    QVariant mFloatString(QByteArray("42.1100006"));
-    QVariant mFloatQString(QString("42.1100006"));
+#ifdef QT_NO_DOUBLECONVERSION
+    // The trailing '2' is not significant, but snprintf doesn't know this.
+    QVariant mFloatString(QByteArray("42.110000610351562"));
+    QVariant mFloatQString(QString("42.110000610351562"));
+#else
+    QVariant mFloatString(QByteArray("42.11000061035156"));
+    QVariant mFloatQString(QString("42.11000061035156"));
+#endif
 
     QVariant mLongLong((qlonglong)-42);
     QVariant mLongLongString(QByteArray("-42"));
@@ -3374,10 +3399,11 @@ void tst_QVariant::numericalConvert()
     switch (v.userType())
     {
     case QVariant::Double:
-        QCOMPARE(v.toString() , QString::number(num, 'g', DBL_MANT_DIG * std::log10(2.) + 2));
+        QCOMPARE(v.toString() , QString::number(num, 'g', QLocale::FloatingPointShortest));
         break;
     case QMetaType::Float:
-        QCOMPARE(v.toString() , QString::number(float(num), 'g', FLT_MANT_DIG * std::log10(2.) + 2));
+        QCOMPARE(v.toString() ,
+                 QString::number(float(num), 'g', QLocale::FloatingPointShortest));
         break;
     }
 }
@@ -3613,8 +3639,17 @@ void tst_QVariant::moreCustomTypes()
     QCOMPARE(MyNotMovable::count, 0);
 
     {
+#ifdef QT_NO_DOUBLECONVERSION
+        // snprintf cannot do "shortest" conversion and always adds noise.
         PLAY_WITH_VARIANT(12.12, false, "12.119999999999999", 12.12, true);
-        PLAY_WITH_VARIANT(12.12f, false, "12.1199999", 12.12f, true);
+#else
+        // Double can be printed exactly with libdouble-conversion
+        PLAY_WITH_VARIANT(12.12, false, "12.12", 12.12, true);
+#endif
+
+        // Float is converted to double, adding insignificant bits
+        PLAY_WITH_VARIANT(12.12f, false, "12.119999885559082", 12.12f, true);
+
         PLAY_WITH_VARIANT('a', false, "a", 'a', true);
         PLAY_WITH_VARIANT((unsigned char)('a'), false, "a", 'a', true);
         PLAY_WITH_VARIANT( quint8(12), false, "\xc", 12, true);
diff --git a/tests/auto/corelib/tools/qlocale/test/test.pro b/tests/auto/corelib/tools/qlocale/test/test.pro
index bb12758107..4777030dd7 100644
--- a/tests/auto/corelib/tools/qlocale/test/test.pro
+++ b/tests/auto/corelib/tools/qlocale/test/test.pro
@@ -4,6 +4,10 @@ QT = core testlib core-private
 embedded: QT += gui
 SOURCES = ../tst_qlocale.cpp
 
+!contains(QT_CONFIG, doubleconversion):!contains(QT_CONFIG, system-doubleconversion) {
+    DEFINES += QT_NO_DOUBLECONVERSION
+}
+
 TARGET = ../tst_qlocale
 win32 {
     CONFIG(debug, debug|release) {
diff --git a/tests/auto/corelib/tools/qlocale/tst_qlocale.cpp b/tests/auto/corelib/tools/qlocale/tst_qlocale.cpp
index 96b91f4fd4..683f7490e5 100644
--- a/tests/auto/corelib/tools/qlocale/tst_qlocale.cpp
+++ b/tests/auto/corelib/tools/qlocale/tst_qlocale.cpp
@@ -772,20 +772,28 @@ void tst_QLocale::doubleToString_data()
     QTest::addColumn<char>("mode");
     QTest::addColumn<int>("precision");
 
-    QTest::newRow("C 3.4 f 5")  << QString("C") << QString("3.40000")     << 3.4 << 'f' << 5;
-    QTest::newRow("C 3.4 f 0")  << QString("C") << QString("3")           << 3.4 << 'f' << 0;
-    QTest::newRow("C 3.4 e 5")  << QString("C") << QString("3.40000e+00") << 3.4 << 'e' << 5;
-    QTest::newRow("C 3.4 e 0")  << QString("C") << QString("3e+00")       << 3.4 << 'e' << 0;
-    QTest::newRow("C 3.4 g 5")  << QString("C") << QString("3.4")         << 3.4 << 'g' << 5;
-    QTest::newRow("C 3.4 g 1")  << QString("C") << QString("3")           << 3.4 << 'g' << 1;
-
-    QTest::newRow("C 3.4 f 1")  << QString("C") << QString("3.4")     << 3.4 << 'f' << 1;
-    QTest::newRow("C 3.4 e 1")  << QString("C") << QString("3.4e+00") << 3.4 << 'e' << 1;
-    QTest::newRow("C 3.4 g 2")  << QString("C") << QString("3.4")     << 3.4 << 'g' << 2;
-
-    QTest::newRow("de_DE 3,4 f 1")  << QString("de_DE") << QString("3,4")     << 3.4 << 'f' << 1;
-    QTest::newRow("de_DE 3,4 e 1")  << QString("de_DE") << QString("3,4e+00") << 3.4 << 'e' << 1;
-    QTest::newRow("de_DE 3,4 g 2")  << QString("de_DE") << QString("3,4")     << 3.4 << 'g' << 2;
+    int shortest = QLocale::FloatingPointShortest;
+
+    QTest::newRow("C 3.4 f 5") << QString("C") << QString("3.40000")     << 3.4 << 'f' << 5;
+    QTest::newRow("C 3.4 f 0") << QString("C") << QString("3")           << 3.4 << 'f' << 0;
+    QTest::newRow("C 3.4 e 5") << QString("C") << QString("3.40000e+00") << 3.4 << 'e' << 5;
+    QTest::newRow("C 3.4 e 0") << QString("C") << QString("3e+00")       << 3.4 << 'e' << 0;
+    QTest::newRow("C 3.4 g 5") << QString("C") << QString("3.4")         << 3.4 << 'g' << 5;
+    QTest::newRow("C 3.4 g 1") << QString("C") << QString("3")           << 3.4 << 'g' << 1;
+
+    QTest::newRow("C 3.4 f 1") << QString("C") << QString("3.4")     << 3.4 << 'f' << 1;
+    QTest::newRow("C 3.4 f -") << QString("C") << QString("3.4")     << 3.4 << 'f' << shortest;
+    QTest::newRow("C 3.4 e 1") << QString("C") << QString("3.4e+00") << 3.4 << 'e' << 1;
+    QTest::newRow("C 3.4 e -") << QString("C") << QString("3.4e+00") << 3.4 << 'e' << shortest;
+    QTest::newRow("C 3.4 g 2") << QString("C") << QString("3.4")     << 3.4 << 'g' << 2;
+    QTest::newRow("C 3.4 g -") << QString("C") << QString("3.4")     << 3.4 << 'g' << shortest;
+
+    QTest::newRow("de_DE 3,4 f 1") << QString("de_DE") << QString("3,4")     << 3.4 << 'f' << 1;
+    QTest::newRow("de_DE 3,4 f -") << QString("de_DE") << QString("3,4")     << 3.4 << 'f' << shortest;
+    QTest::newRow("de_DE 3,4 e 1") << QString("de_DE") << QString("3,4e+00") << 3.4 << 'e' << 1;
+    QTest::newRow("de_DE 3,4 e -") << QString("de_DE") << QString("3,4e+00") << 3.4 << 'e' << shortest;
+    QTest::newRow("de_DE 3,4 g 2") << QString("de_DE") << QString("3,4")     << 3.4 << 'g' << 2;
+    QTest::newRow("de_DE 3,4 g -") << QString("de_DE") << QString("3,4")     << 3.4 << 'g' << shortest;
 
     QTest::newRow("C 0.035003945 f 12") << QString("C") << QString("0.035003945000")   << 0.035003945 << 'f' << 12;
     QTest::newRow("C 0.035003945 f 6")  << QString("C") << QString("0.035004")         << 0.035003945 << 'f' << 6;
@@ -794,13 +802,19 @@ void tst_QLocale::doubleToString_data()
     QTest::newRow("C 0.035003945 g 11") << QString("C") << QString("0.035003945")      << 0.035003945 << 'g' << 11;
     QTest::newRow("C 0.035003945 g 5")  << QString("C") << QString("0.035004")         << 0.035003945 << 'g' << 5;
 
-    QTest::newRow("C 0.035003945 f 9")  << QString("C") << QString("0.035003945")   << 0.035003945 << 'f' << 9;
-    QTest::newRow("C 0.035003945 e 7")  << QString("C") << QString("3.5003945e-02") << 0.035003945 << 'e' << 7;
-    QTest::newRow("C 0.035003945 g 8")  << QString("C") << QString("0.035003945")   << 0.035003945 << 'g' << 8;
+    QTest::newRow("C 0.035003945 f 9") << QString("C") << QString("0.035003945")   << 0.035003945 << 'f' << 9;
+    QTest::newRow("C 0.035003945 f -") << QString("C") << QString("0.035003945")   << 0.035003945 << 'f' << shortest;
+    QTest::newRow("C 0.035003945 e 7") << QString("C") << QString("3.5003945e-02") << 0.035003945 << 'e' << 7;
+    QTest::newRow("C 0.035003945 e -") << QString("C") << QString("3.5003945e-02") << 0.035003945 << 'e' << shortest;
+    QTest::newRow("C 0.035003945 g 8") << QString("C") << QString("0.035003945")   << 0.035003945 << 'g' << 8;
+    QTest::newRow("C 0.035003945 g -") << QString("C") << QString("0.035003945")   << 0.035003945 << 'g' << shortest;
 
-    QTest::newRow("de_DE 0,035003945 f 9")  << QString("de_DE") << QString("0,035003945")   << 0.035003945 << 'f' << 9;
-    QTest::newRow("de_DE 0,035003945 e 7")  << QString("de_DE") << QString("3,5003945e-02") << 0.035003945 << 'e' << 7;
-    QTest::newRow("de_DE 0,035003945 g 8")  << QString("de_DE") << QString("0,035003945")   << 0.035003945 << 'g' << 8;
+    QTest::newRow("de_DE 0,035003945 f 9") << QString("de_DE") << QString("0,035003945")   << 0.035003945 << 'f' << 9;
+    QTest::newRow("de_DE 0,035003945 f -") << QString("de_DE") << QString("0,035003945")   << 0.035003945 << 'f' << shortest;
+    QTest::newRow("de_DE 0,035003945 e 7") << QString("de_DE") << QString("3,5003945e-02") << 0.035003945 << 'e' << 7;
+    QTest::newRow("de_DE 0,035003945 e -") << QString("de_DE") << QString("3,5003945e-02") << 0.035003945 << 'e' << shortest;
+    QTest::newRow("de_DE 0,035003945 g 8") << QString("de_DE") << QString("0,035003945")   << 0.035003945 << 'g' << 8;
+    QTest::newRow("de_DE 0,035003945 g -") << QString("de_DE") << QString("0,035003945")   << 0.035003945 << 'g' << shortest;
 
     QTest::newRow("C 0.000003945 f 12") << QString("C") << QString("0.000003945000") << 0.000003945 << 'f' << 12;
     QTest::newRow("C 0.000003945 f 6")  << QString("C") << QString("0.000004")       << 0.000003945 << 'f' << 6;
@@ -809,13 +823,19 @@ void tst_QLocale::doubleToString_data()
     QTest::newRow("C 0.000003945 g 7")  << QString("C") << QString("3.945e-06")      << 0.000003945 << 'g' << 7;
     QTest::newRow("C 0.000003945 g 1")  << QString("C") << QString("4e-06")          << 0.000003945 << 'g' << 1;
 
-    QTest::newRow("C 0.000003945 f 9")  << QString("C") << QString("0.000003945") << 0.000003945 << 'f' << 9;
-    QTest::newRow("C 0.000003945 e 3")  << QString("C") << QString("3.945e-06")   << 0.000003945 << 'e' << 3;
-    QTest::newRow("C 0.000003945 g 4")  << QString("C") << QString("3.945e-06")   << 0.000003945 << 'g' << 4;
+    QTest::newRow("C 0.000003945 f 9") << QString("C") << QString("0.000003945") << 0.000003945 << 'f' << 9;
+    QTest::newRow("C 0.000003945 f -") << QString("C") << QString("0.000003945") << 0.000003945 << 'f' << shortest;
+    QTest::newRow("C 0.000003945 e 3") << QString("C") << QString("3.945e-06")   << 0.000003945 << 'e' << 3;
+    QTest::newRow("C 0.000003945 e -") << QString("C") << QString("3.945e-06")   << 0.000003945 << 'e' << shortest;
+    QTest::newRow("C 0.000003945 g 4") << QString("C") << QString("3.945e-06")   << 0.000003945 << 'g' << 4;
+    QTest::newRow("C 0.000003945 g -") << QString("C") << QString("3.945e-06")   << 0.000003945 << 'g' << shortest;
 
-    QTest::newRow("de_DE 0,000003945 f 9")  << QString("de_DE") << QString("0,000003945") << 0.000003945 << 'f' << 9;
-    QTest::newRow("de_DE 0,000003945 e 3")  << QString("de_DE") << QString("3,945e-06")   << 0.000003945 << 'e' << 3;
-    QTest::newRow("de_DE 0,000003945 g 4")  << QString("de_DE") << QString("3,945e-06")   << 0.000003945 << 'g' << 4;
+    QTest::newRow("de_DE 0,000003945 f 9") << QString("de_DE") << QString("0,000003945") << 0.000003945 << 'f' << 9;
+    QTest::newRow("de_DE 0,000003945 f -") << QString("de_DE") << QString("0,000003945") << 0.000003945 << 'f' << shortest;
+    QTest::newRow("de_DE 0,000003945 e 3") << QString("de_DE") << QString("3,945e-06")   << 0.000003945 << 'e' << 3;
+    QTest::newRow("de_DE 0,000003945 e -") << QString("de_DE") << QString("3,945e-06")   << 0.000003945 << 'e' << shortest;
+    QTest::newRow("de_DE 0,000003945 g 4") << QString("de_DE") << QString("3,945e-06")   << 0.000003945 << 'g' << 4;
+    QTest::newRow("de_DE 0,000003945 g -") << QString("de_DE") << QString("3,945e-06")   << 0.000003945 << 'g' << shortest;
 
     QTest::newRow("C 12456789012 f 3")  << QString("C") << QString("12456789012.000")     << 12456789012.0 << 'f' << 3;
     QTest::newRow("C 12456789012 e 13") << QString("C") << QString("1.2456789012000e+10") << 12456789012.0 << 'e' << 13;
@@ -824,12 +844,18 @@ void tst_QLocale::doubleToString_data()
     QTest::newRow("C 12456789012 g 8")  << QString("C") << QString("1.2456789e+10")       << 12456789012.0 << 'g' << 8;
 
     QTest::newRow("C 12456789012 f 0")  << QString("C") << QString("12456789012")      << 12456789012.0 << 'f' << 0;
+    QTest::newRow("C 12456789012 f -")  << QString("C") << QString("12456789012")      << 12456789012.0 << 'f' << shortest;
     QTest::newRow("C 12456789012 e 10") << QString("C") << QString("1.2456789012e+10") << 12456789012.0 << 'e' << 10;
+    QTest::newRow("C 12456789012 e -")  << QString("C") << QString("1.2456789012e+10") << 12456789012.0 << 'e' << shortest;
     QTest::newRow("C 12456789012 g 11") << QString("C") << QString("12456789012")      << 12456789012.0 << 'g' << 11;
+    QTest::newRow("C 12456789012 g -")  << QString("C") << QString("12456789012")      << 12456789012.0 << 'g' << shortest;
 
     QTest::newRow("de_DE 12456789012 f 0")  << QString("de_DE") << QString("12.456.789.012")   << 12456789012.0 << 'f' << 0;
+    QTest::newRow("de_DE 12456789012 f -")  << QString("de_DE") << QString("12.456.789.012")   << 12456789012.0 << 'f' << shortest;
     QTest::newRow("de_DE 12456789012 e 10") << QString("de_DE") << QString("1,2456789012e+10") << 12456789012.0 << 'e' << 10;
+    QTest::newRow("de_DE 12456789012 e -")  << QString("de_DE") << QString("1,2456789012e+10") << 12456789012.0 << 'e' << shortest;
     QTest::newRow("de_DE 12456789012 g 11") << QString("de_DE") << QString("12.456.789.012")   << 12456789012.0 << 'g' << 11;
+    QTest::newRow("de_DE 12456789012 g -")  << QString("de_DE") << QString("12.456.789.012")   << 12456789012.0 << 'g' << shortest;
 }
 
 void tst_QLocale::doubleToString()
@@ -840,6 +866,11 @@ void tst_QLocale::doubleToString()
     QFETCH(char, mode);
     QFETCH(int, precision);
 
+#ifdef QT_NO_DOUBLECONVERSION
+    if (precision == QLocale::FloatingPointShortest)
+        QSKIP("'Shortest' double conversion is not that short without libdouble-conversion");
+#endif
+
     const QLocale locale(locale_name);
     QCOMPARE(locale.toString(num, mode, precision), num_str);