Method plus

base/src/main/java/net/time4j/MachineTime.java:599–646

(
        long amount,
        U unit
    )

     * @since   2.0
     */
    public MachineTime<U> plus(
        long amount,
        U unit
    ) {

        long s = this.seconds;
        int f = this.nanos;

        if (this.scale == POSIX) {
            TimeUnit u = TimeUnit.class.cast(unit);

            if (u.compareTo(TimeUnit.SECONDS) >= 0) {
                s =
                    Math.addExact(
                        s,
                        Math.multiplyExact(
                            amount,
                            TimeUnit.SECONDS.convert(1, u))
                    );
            } else {
                long total =
                    Math.addExact(
                        f,
                        Math.multiplyExact(
                            amount,
                            TimeUnit.NANOSECONDS.convert(1, u))
                    );
                s = Math.addExact(s, Math.floorDiv(total, MRD));
                f = (int) Math.floorMod(total, MRD);
            }
        } else {
            switch (SI.class.cast(unit)) {
                case SECONDS:
                    s = Math.addExact(s, amount);
                    break;
                case NANOSECONDS:
                    long total = Math.addExact(f, amount);
                    s = Math.addExact(s, Math.floorDiv(total, MRD));
                    f = (int) Math.floorMod(total, MRD);
                    break;
                default:
                    throw new UnsupportedOperationException(unit.toString());
            }
        }

        return new MachineTime<>(s, f, this.scale);

    }

    /**
     * <p>Add given temporal amount to this machine time. </p>