function bnSubtract(a) {
        var r = nbi();
        this.subTo(a, r);
        return r;
    }

// (public) this * a
    function bnMultiply(a) {
        var r = nbi();
        this.multiplyTo(a, r);
        return r;
    }

// (public) this^2
    function bnSquare() {
        var r = nbi();
        this.squareTo(r);
        return r;
    }

// (public) this / a
    function bnDivide(a) {
        var r = nbi();
        this.divRemTo(a, r, null);
        return r;
    }

// (public) this % a
    function 