This is a two wide tileable full adder. That means that you can put them next to each other and they will not mess eachother up in any way. Whats special about this one is that the Carry Out feeds directly into the Carry in of the next one. Unfortunately to make the inputs easier to access one of them has to be powered to be off. You can see why.

I don't really know about speed, but meh. I think its about 6 or 8 ticks.

And yes, the button is needed. It makes the torch realise its being powered, else the whole lot won't work.

The one in the save file is two of them, only to show where the torch needs to be placed to make it work.

This was done because I wanted to improve upon my chunky 32bit ripple adder, which uses a modified version of this. I can make it a whole 64 blocks smaller! A lot more busing though...

This is color coded to fit with TaviRiders world of redstone, that being, Green is gate, Blue is output, Red is input, light blue is insulator, light gray showing that a torch is powering it.

Thanks to Shrogg for figuring out a way to get the carry to work. Doesn't matter how obvious it was...