Use numeric_limits instead of hand-coded equivalents

As a comment noted, the reason for QLocaleData rolling its own values
describing the ranges of digits and exponents in a double were all
about std::numeric_limits's constants not being constexpr - which they
have now been since C++11, so we can do away with our own.

One of the constants was used in two places in the same way; so
abstract that use out into an inline function in qlocale_tools, to
save duplication and give somewhere to document it.

Change-Id: I7e3740ece9b499c0ec434de18d70abe69e1fe079
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 7 insertions, 6 deletions

diff --git a/src/corelib/text/qlocale_tools.cpp b/src/corelib/text/qlocale_tools.cpp
index a1838add72..874f42c8e5 100644
--- a/src/corelib/text/qlocale_tools.cpp
+++ b/src/corelib/text/qlocale_tools.cpp
@@ -139,7 +139,7 @@ void qt_doubleToAscii(double d, QLocaleData::DoubleForm form, int precision, cha
     if (precision > 999)
         precision = 999;
     else if (precision == QLocale::FloatingPointShortest)
-        precision = QLocaleData::DoubleMaxSignificant; // "shortest" mode not supported by snprintf
+        precision = std::numeric_limits<double>::max_digits10; // snprintf lacks "shortest" mode
 
     if (isZero(d)) {
         // Negative zero is expected as simple "0", not "-0". We cannot do d < 0, though.
@@ -167,8 +167,8 @@ void qt_doubleToAscii(double d, QLocaleData::DoubleForm form, int precision, cha
     switch (form) {
     case QLocaleData::DFDecimal:
         format[formatLength - 2] = 'f';
-        // <anything> '.' <precision> '\0' - optimize for numbers smaller than 512k
-        extraChars = (d > (1 << 19) ? QLocaleData::DoubleMaxDigitsBeforeDecimal : 6) + 2;
+        // <anything> '.' <precision> '\0'
+        extraChars = wholePartSpace(d) + 2;
         break;
     case QLocaleData::DFExponent:
         format[formatLength - 2] = 'e';
@@ -581,9 +581,10 @@ QString qdtoa(qreal d, int *decpt, int *sign)
     int length = 0;
 
     // Some versions of libdouble-conversion like an extra digit, probably for '\0'
-    char result[QLocaleData::DoubleMaxSignificant + 1];
-    qt_doubleToAscii(d, QLocaleData::DFSignificantDigits, QLocale::FloatingPointShortest, result,
-                     QLocaleData::DoubleMaxSignificant + 1, nonNullSign, length, nonNullDecpt);
+    constexpr int digits = std::numeric_limits<double>::max_digits10 + 1;
+    char result[digits];
+    qt_doubleToAscii(d, QLocaleData::DFSignificantDigits, QLocale::FloatingPointShortest,
+                     result, digits, nonNullSign, length, nonNullDecpt);
 
     if (sign)
         *sign = nonNullSign ? 1 : 0;