http://benji3up2kxewkqfcq7buxk2xd6zwy3zggnurkrm3l4cvwy2iipvyyad.onion/mirrors/gmpdoc/Single-Limb-Division.html
The calculation is
basically the same, but the inverse is two limbs and the divisor treated as if
padded with a low zero limb. This means more work, since the inverse will
need a 2x2 multiply, but the four 1x1s to do that are
independent and can therefore be done partly or wholly in parallel. Likewise
for a 2x1 calculating q*d .