Replace qdtoa and qstrtod implementation by a 3rdparty library

This also fixes the underlying cause of QTBUG-44039 and QTBUG-43885.

You can choose between system, qt, and no libdouble-conversion
support. If you choose "no", snprintf_l and sscanf_l will be
used.

By default, system double conversion is used if the system provides a
double-conversion library. Otherwise the bundled libdouble-conversion
is built. sscanf_l and snprintf_l are not used by default as the
planned "shortest" conversion mode to produce the shortest possible
string will give less precise results when implemented with snprintf_l.

Change-Id: I8ca08a0fca5c54cf7009e48e771385614f6aa031
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/corelib/tools/qlocale_p.h b/src/corelib/tools/qlocale_p.h
index b3fd7a96b8..d943612ff1 100644
--- a/src/corelib/tools/qlocale_p.h
+++ b/src/corelib/tools/qlocale_p.h
@@ -165,6 +165,17 @@ public:
                                              QLocale::Country country);
     static const QLocaleData *c();
 
+    // Maximum number of significant digits needed to represent a double.
+    // We cannot use std::numeric_limits here without constexpr.
+    static const int DoubleMantissaBits = 53;
+    static const int Log10_2_100000 = 30103;    // log10(2) * 100000
+    // same as C++11 std::numeric_limits<T>::max_digits10
+    static const int DoubleMaxSignificant = (DoubleMantissaBits * Log10_2_100000) / 100000 + 2;
+
+    // Maximum number of digits before decimal point to represent a double
+    // Same as std::numeric_limits<double>::max_exponent10 + 1
+    static const int DoubleMaxDigitsBeforeDecimal = 309;
+
     enum DoubleForm {
         DFExponent = 0,
         DFDecimal,