bn_check_top(r);
BIGNUM *BN_dup(const BIGNUM *a)	{	BIGNUM *r, *t;	if (a == NULL) return NULL;	bn_check_top(a);	t = BN_new();	if (t == NULL) return(NULL);	r = BN_copy(t, a);	/* now  r == t || r == NULL */	if (r == NULL)		BN_free(t);	return r;	}