Json writer, emit full precision for floating point Number types

Previously Qt JSON writer would only emit 6 digits of precision as this
is the default with the formatter.

However with testing against NodeJS JSON.stringify() this behavior is
inconsistent with the defacto standard JSON implementation and conveys
a loss of precision.

Change-Id: Ie1845a6e0ee0b4c05f63ec0062f372e891855f0b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/tests/auto/corelib/json/tst_qtjson.cpp b/tests/auto/corelib/json/tst_qtjson.cpp
index 7cdf6deb87..bbc137d688 100644
--- a/tests/auto/corelib/json/tst_qtjson.cpp
+++ b/tests/auto/corelib/json/tst_qtjson.cpp
@@ -96,6 +96,7 @@ private Q_SLOTS:
 
     void toJson();
     void toJsonSillyNumericValues();
+    void toJsonLargeNumericValues();
     void fromJson();
     void fromJsonErrors();
     void fromBinary();
@@ -1110,6 +1111,57 @@ void tst_QtJson::toJsonSillyNumericValues()
     QCOMPARE(json, expected);
 }
 
+void tst_QtJson::toJsonLargeNumericValues()
+{
+    QJsonObject object;
+    QJsonArray array;
+    array.append(QJsonValue(1.234567)); // actual precision bug in Qt 5.0.0
+    array.append(QJsonValue(1.7976931348623157e+308)); // JS Number.MAX_VALUE
+    array.append(QJsonValue(5e-324));                  // JS Number.MIN_VALUE
+    array.append(QJsonValue(std::numeric_limits<double>::min()));
+    array.append(QJsonValue(std::numeric_limits<double>::max()));
+    array.append(QJsonValue(std::numeric_limits<double>::epsilon()));
+    array.append(QJsonValue(std::numeric_limits<double>::denorm_min()));
+    array.append(QJsonValue(0.0));
+    array.append(QJsonValue(-std::numeric_limits<double>::min()));
+    array.append(QJsonValue(-std::numeric_limits<double>::max()));
+    array.append(QJsonValue(-std::numeric_limits<double>::epsilon()));
+    array.append(QJsonValue(-std::numeric_limits<double>::denorm_min()));
+    array.append(QJsonValue(-0.0));
+    object.insert("Array", array);
+
+    QByteArray json = QJsonDocument(object).toJson();
+
+    QByteArray expected =
+            "{\n"
+            "    \"Array\": [\n"
+            "        1.234567,\n"
+            "        1.7976931348623157e+308,\n"
+            //     ((4.9406564584124654e-324 == 5e-324) == true)
+            // I can only think JavaScript has a special formatter to
+            //  emit this value for this IEEE754 bit pattern.
+            "        4.9406564584124654e-324,\n"
+            "        2.2250738585072014e-308,\n"
+            "        1.7976931348623157e+308,\n"
+            "        2.2204460492503131e-16,\n"
+            "        4.9406564584124654e-324,\n"
+            "        0,\n"
+            "        -2.2250738585072014e-308,\n"
+            "        -1.7976931348623157e+308,\n"
+            "        -2.2204460492503131e-16,\n"
+            "        -4.9406564584124654e-324,\n"
+            "        0\n"
+            "    ]\n"
+            "}\n";
+
+    QCOMPARE(json, expected);
+
+    QJsonDocument doc;
+    doc.setObject(object);
+    json = doc.toJson();
+    QCOMPARE(json, expected);
+}
+
 void tst_QtJson::fromJson()
 {
     {