@Override
    protected void onDeserialize(Deserializer buf) {
        super.onDeserialize(buf);
        int b = buf.getByte(null);
        timePart = TimePart.valueOf(b & 0x7f);
        isGmt = (b & 0x80) != 0;
    }
<p>Create a bucket expression with the given width and the given subexpression.</p>

@param arg  The argument for this function.
@param part The part of time to retrieve.
@param gmt  Whether or not to treat time as GMT.
searchlib/src/main/java/com/yahoo/searchlib/expression/TimeStampFunctionNode.java