@Override
    protected void onDeserialize(Deserializer buf) {
        super.onDeserialize(buf);
        int b = buf.getByte(null);
        fnc = Function.valueOf(b & 0xff);
    }
This function is an instruction to negate its argument.

@author baldersheim
@author Simon Thoresen Hult
searchlib/src/main/java/com/yahoo/searchlib/expression/MathFunctionNode.java