private void findPrevious() {

		try {
			long prevIndex = pm.getPreviousPropertyIndex(current);
            if (hasBoundaries && prevIndex < start) {
                doesHavePrevious = false;
                return;
            }
			current = prevIndex;
            doesHavePrevious = true;
            doesHaveNext = false;
		} catch (NoSuchIndexException e) {
			return;
		}
	}
Return whether there is a previous index; if there is,
"currentPrevious" has the value.
Ghidra/Framework/Generic/src/main/java/ghidra/util/map/LongIteratorImpl.java