Commentary updates and minor optimization for bn_mont.c.

		size_t m1,m2;

		v=bn_sub_words(rp,ap,mont->N.d,ri);

		/* if (al==ri && !v) || al>ri)	nrp=rp; */

		/* this -----------------------^^ works even in al<ri case

		 * thanks to zealous zeroing of top of the vector in the

		 * beginning. */

		/* if (al==ri && !v) || al>ri) nrp=rp; else nrp=ap; */

		/* in other words if subtraction result is real, then

		 * trick unconditional memcpy below to make "refresh"

		 * instead of real copy. */

		 * trick unconditional memcpy below to perform in-place

		 * "refresh" instead of actual copy. */

		m1=0-(size_t)(((al-ri)>>(sizeof(al)*8-1))&1);	/* al<ri */

		m2=0-(size_t)(((ri-al)>>(sizeof(al)*8-1))&1);	/* al>ri */

		m1=~(m1|m2);		/* (al==ri) */

		m1&=~(0-(size_t)v);	/* (al==ri && !v) */

		m1|=m2;			/* (al==ri && !v) || al>ri */

		nrp=(BN_ULONG *)(((size_t)rp&m1)|((size_t)ap&~m1));

		m1|=m2;			/* (al!=ri) */

		m1|=(0-(size_t)v);	/* (al!=ri || v) */

		m1&=~m2;		/* (al!=ri || v) && !al>ri */

		nrp=(BN_ULONG *)(((size_t)rp&~m1)|((size_t)ap&m1));

		}

	/* 'i<ri' is chosen to eliminate dependency on input data, even

	 * though it results in redundant copy in al<ri case. */

	for (i=0,ri-=4; i<ri; i+=4)

		{

		BN_ULONG t1,t2,t3,t4;