private SexFormat(boolean useSign, int dp3) {
            this.useSign = useSign;
            this.dp3 = dp3;
            if (dp3 < 0) {
                throw new IllegalArgumentException();
            }
            buf = new char[(useSign ? 1 : 0) + 2 + 6 + ((dp3 > 0) ? 1 : 0) + dp3];
        }