Division Method
===============

Dividing a 256-bit block by a 128-bit number of the form B-3i. We are given:

	a = {mx, {x3, x2, x1, x0}}	Number to divide
	d = {b1, b0}			Divisor

Declare

	q = {0, {0, 0, 0, 0}}		Quotient we build
	r = {0, {0, mx, x3, x2}}	Collecting remainder

Algorithm:

	while r >= d:
		q.x[2]++
		r = r - d

	r = {0, {r.mx, r.x1, r.x2, a.x1}}

	while r >= d:
		q.x[1]++
		r = r - d

	r = {r.mx, {r.x2, r.x1, r.x0, a.x0}}

	while r >= d:
		q.x[0]++
		r = r - d

At the end, the remainder has the correct value, and the quotient is in q.