Qt Json to XML

class JsonToXml{
    static int guessPrecision(double val){
        double junk;
        int precision = 0;
        for(;!qFuzzyIsNull(std::modf(val,&junk));++precision)
            val*=10.0;
        return precision;
    }
    static void jsonValueToXml(const QJsonValue& val, const QString& name, QXmlStreamWriter& writer){
        if(val.isNull() || val.isUndefined())
            return;
        if(val.isObject())
            return jsonObjectToXml(val.toObject(),name,writer);
        if(val.isArray())
            return jsonArrayToXml(val.toArray(),name,writer);
         writer.writeStartElement(name);
         writer.writeAttribute(QStringLiteral("type"),QStringLiteral("value"));
         if(val.isBool()){
             writer.writeAttribute(QStringLiteral("valueType"),QStringLiteral("boolean"));
             writer.writeCharacters(val.toBool() ? QStringLiteral("true") : QStringLiteral("false"));
         }
         else if(val.isDouble()){
             writer.writeAttribute(QStringLiteral("valueType"),QStringLiteral("double"));
             const double doubleVal = val.toDouble();
             writer.writeCharacters(QString::number(doubleVal,'f',guessPrecision(doubleVal)));
         }
         else{
             writer.writeAttribute(QStringLiteral("valueType"),QStringLiteral("string"));
             writer.writeCharacters(val.toString());
         }
         writer.writeEndElement();
    }
    static void jsonObjectToXml(const QJsonObject& obj, const QString& name, QXmlStreamWriter& writer ){
        if(obj.isEmpty())
            return;
        writer.writeStartElement(name);
        writer.writeAttribute(QStringLiteral("type"),QStringLiteral("object"));
        for(auto i=obj.constBegin(), objEnd = obj.constEnd();i!=objEnd;++i)
            jsonValueToXml(*i,i.key(),writer);
        writer.writeEndElement();
    }
    static void jsonArrayToXml(const QJsonArray& arr, const QString& name, QXmlStreamWriter& writer ){
        writer.writeStartElement(name);
        writer.writeAttribute(QStringLiteral("type"),QStringLiteral("array"));
        for(int i=0, arrSize= arr.size();i<arrSize;++i)
            jsonValueToXml(arr.at(i),name + QString::number(i),writer);
        writer.writeEndElement();
    }
public:
    static QString jsonToXml(const QJsonDocument& doc, const QString& rootElementName = "root"){
        QString result;
        if(doc.isEmpty() || doc.isNull())
            return result;
        QXmlStreamWriter writer(&result);
        writer.writeStartDocument();
        if(doc.isArray())
            jsonArrayToXml(doc.array(),rootElementName,writer);
        else if(doc.isObject())
            jsonObjectToXml(doc.object(),rootElementName,writer);
        return result;
    }
};