I recently came across carry look-ahead adder(CLA) in David and Sarah Harris's book(Digital Design and Computer Architecture). The circuitry for a 64 bit number (standard integer size in C) is probably huge and gets very complicated.The generate function has just too many gates.

My question is: are CLAs used in current processors such as the Intel i3 or in similar series? Also, are there any better implementations of carry adders?

I am aware of the fact that older processors like the Intel 8008 and the kind did use a CLA.

  • 2
    $\begingroup$ cs.stackexchange.com/questions/29368/… $\endgroup$ Commented Mar 28, 2019 at 17:36
  • $\begingroup$ Thank you @Emil. I did see the answer you mentioned prior to asking this question. The answers there were did not satisfy my curiosity. Hence this question. $\endgroup$
    – Shubhayu
    Commented Mar 29, 2019 at 15:38

1 Answer 1


“Huge and complicated” is no problem, as long as it is fast. It isn’t.

A good choice seems to be a conditional sum adder (CSA) which has a total delay of O(log n) gates. Log n is nice for 64 bit adders.


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