2 Bit Adder: Inputs 0,1,0,1 Outputs

[SatellitePlus]

Hello! I've been working out the truth table to a logic gate which I've been told is a 2 Bit Adder. The inputs, in the order of the truth table below are 0, 1, 0, 1.

Inputs:                         Outputs: 
0	0	0	0	0	0	0
1	0	0	0	0	1	0
0	1	0	0	0	0	1
0	0	1	0	0	1	0
0	0	0	1	0	0	1
1	1	0	0	0	1	1
1	0	1	0	1	0	0
1	0	0	1	0	1	1
0	1	1	0	1	1	0
0	1	0	1	0	1	0
0	0	1	1	0	1	1
1	1	1	0	1	0	1
1	1	0	1	1	0	0
0	1	1	1	1	0	0
1	0	1	1	1	0	1
1	1	1	1	1	1	0

So can anyone tell me why this is a 2 bit adder? Just from the truth table. My guess would be that the outputs are never all ones, but I think that's just half the story. And how would I go about making a 3 bit adder?

 

[Janus]

I'd say its because if you take to the first two inputs as a 2 bit binary number and the second two inputs as another 2 bit binary number, the three outputs will give the sum of these two numbers as a three bit binary number. However, there appears to be a mistake on the 9th line. 01+10 does not equal 110, but instead 011. (1+2 does not equal 6, but instead 3)