http://benji3up2kxewkqfcq7buxk2xd6zwy3zggnurkrm3l4cvwy2iipvyyad.onion/mirrors/gmpdoc/Assembly-Loop-Unrolling.html
The limbs not a multiple of the unrolling can be handled in various ways, for
example A simple loop at the end (or the start) to process the excess. Care will be
wanted that it isn’t too much slower than the unrolled part. A set of binary tests, for example after an 8-limb unrolling, test for 4 more
limbs to process, then a further 2 more or not, and finally 1 more or not.