I suppose if you used a minicomputer in the 70s or 80s then you used this or something like this chip. This is another site giving some more history and data sheets of the 74181 [1].<p>The carry-lookahead adder used in the 74181 was patented by IBM in 1957 [2].<p>Carry-lookahead is O(log n) in time and 0(n log n) in space. Carry-skip and carry-save are O(sqrt n) in time and O(n) in space [3].<p>I couldn't figure out what Intel or ARM or even RISC-V use. But according to this [4], full-lookahead for 32b is 5 gate latency while only being 4 times larger than ripple.<p>[1] <a href="https://apollo181.wixsite.com/apollo181/about" rel="nofollow">https://apollo181.wixsite.com/apollo181/about</a><p>[2] <a href="https://patents.google.com/patent/US2966305" rel="nofollow">https://patents.google.com/patent/US2966305</a><p>[3] <a href="https://booksite.elsevier.com/9780123838728/references/appendix_j.pdf" rel="nofollow">https://booksite.elsevier.com/9780123838728/references/appen...</a><p>[4] <a href="http://www.cs.cornell.edu/courses/cs3410/2010sp/lecture/topic08-performance-i.pdf" rel="nofollow">http://www.cs.cornell.edu/courses/cs3410/2010sp/lecture/topi...</a><p>Does anyone know what Intel's Tiger Lake or ARM's A77 or RISC-V BOOM (and I looked at the Chisel source) use?