modal verbs - Is there another way to say "needn't have done"?

I'm learning modal verbs now and get in trouble with "need" one.

In my textbook it is said that:

don't need to == needn't -- present simple
didn't need to -- past simple
needn't have done -- present perfect

In some inexplicable reason I think that needn't have done sounds weird (may be because I haven't ever heard of such construction).

So my question is: Is there a sentence that equal to needn't have done but without the needn't part (like the past simple one)? Or everything is just fine with it and I shouldn't keep in mind?

Answer

Actually, all of the examples are a little weird. Need is very rarely used as a modal any more, and it's likely that you'll be able to go your entire life without ever encountering it in speech. It is sufficient that you be able to recognize and understand sentences like the above, but don't expect to use them much. Just treat need like any other verb:

Present: don't need to

Present perfect: haven't needed to

Simple past: didn't need to

Past perfect: hadn't needed to

That said, the three examples are grammatically correct, strictly speaking. The phrase needn't have done is a fine, though archaic, way of saying didn't need to have done...