Allow Setting Value of GroupObject (KO) with Checking Change after Conversion by valueNoSendCompare(..)

* Return if Value was Changed
* Always Set the First Value
* Copy on Changes Only
* Make Comparison Independent of Sending
* Extend Doc of `valueNoSendCompare(..)`; Add Note for using `valueNoSend(..)`

src/knx/group_object.cpp

@@ -287,3 +287,27 @@ void GroupObject::valueNoSend(const KNXValue& value, const Dpt& type)
 
     KNX_Encode_Value(value, _data, _dataLength, type);
 }
+
+bool GroupObject::valueNoSendCompare(const KNXValue& value, const Dpt& type)
+{
+    if (_commFlag == Uninitialized)
+    {
+        // always set first value
+        this->valueNoSend(value, type);
+        return true;
+    }
+    else
+    {
+        // convert new value to given dtp
+        uint8_t newData[_dataLength];
+        memset(newData, 0, _dataLength);
+        KNX_Encode_Value(value, newData, _dataLength, type);
+
+        // check for change in converted value / update value on change only
+        const bool dataChanged = memcmp(_data, newData, _dataLength);
+        if (dataChanged)
+            memcpy(_data, newData, _dataLength);
+
+        return dataChanged;
+    }
+}

src/knx/group_object.h

@@ -181,6 +181,19 @@ class GroupObject
      * The parameters must fit the group object. Otherwise it will stay unchanged.
      */
     void valueNoSend(const KNXValue& value, const Dpt& type);
+
+    /**
+     * Check if the value (after conversion to dpt) will differ from current value of the group object and update if necessary.
+     * Use this method only, when the value change is relevant, otherwise valueNoSend(const KNXValue&, const Dpt&) will do the same (without overhead for comparing)
+     * @param value the value the group object is set to
+     * @param type the datapoint type used for the conversion.
+     * 
+     * The parameters must fit the group object. Otherwise it will stay unchanged.
+     * 
+     * @returns true if the value of the group object has changed
+     */
+    bool valueNoSendCompare(const KNXValue& value, const Dpt& type);
+
     /**
      * set the current value of the group object.
      * @param value the value the group object is set to