As there was a large amount of discussion, I've attached a truth table for a three input XOR gate, as well as a table showing the pattern for multi-input XOR gates. Hope someone finds it useful.

dj

 

I'll conceed the point as well. If they wanted an adder, one wonders why they didn't just call it an adder.

 

Because it's not exactly an adder. It's a cicuit that tells you if the sum is odd or even, it doesn't give you the sum itself.