If you're interested in even more details you could also have a look at Tom's book about bignum arithmetics. C.f. third paragraph of https://github.com/libtom/l

If you're interested in even more details you could also have a look at Tom's book about bignum arithmetics. C.f. third paragraph of https://github.com/libtom/libtommath#summary https://github.com/libtom/libtommath#summary The library evolved since then, so the algorithm documentation only exists in code nowadays. FTR I'm involved in the project as maintainer.