Method between

base/src/main/java/net/time4j/Moment.java:2646–2705

(
            Moment start,
            Moment end
        )

        }

        @Override
        public long between(
            Moment start,
            Moment end
        ) {

            long delta;

            if (this.unit.compareTo(TimeUnit.SECONDS) >= 0) {
                delta = (end.getPosixTime() - start.getPosixTime());
                if (delta < 0) {
                    if (end.getNanosecond() > start.getNanosecond()) {
                        delta++;
                    }
                } else if (delta > 0) {
                    if (end.getNanosecond() < start.getNanosecond()) {
                        delta--;
                    }
                }
            } else { // MILLIS, MICROS, NANOS
                delta =
                    Math.addExact(
                        Math.multiplyExact(
                            Math.subtractExact(
                                end.getPosixTime(),
                                start.getPosixTime()
                            ),
                            MRD
                        ),
                        end.getNanosecond() - start.getNanosecond()
                    );
            }

            switch (this.unit) {
                case DAYS:
                    delta = delta / 86400;
                    break;
                case HOURS:
                    delta = delta / 3600;
                    break;
                case MINUTES:
                    delta = delta / 60;
                    break;
                case SECONDS:
                    break;
                case MILLISECONDS:
                    delta = delta / MIO;
                    break;
                case MICROSECONDS:
                    delta = delta / 1000;
                    break;
                case NANOSECONDS:
                    break;
                default:
                    throw new UnsupportedOperationException(this.unit.name());
            }

            return delta;