bn_wexpand(r, at->top);
bn_expand2(r, at->top);
int	BN_GF2m_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)	{	int i;	const BIGNUM *at, *bt;	if (a->top < b->top) { at = b; bt = a; }	else { at = a; bt = b; }	bn_wexpand(r, at->top);	for (i = 0; i < bt->top; i++)		{		r->d[i] = at->d[i] ^ bt->d[i];		}	for (; i < at->top; i++)		{		r->d[i] = at->d[i];		}		r->top = at->top;	bn_fix_top(r);		return 1;	}