function BigInteger(a, b, c) {
        if (a != null)
            if ("number" == typeof a) this.fromNumber(a, b, c);
            else if (b == null && "string" != typeof a) this.fromString(a, 256);
        else this.fromString(a, b);
    }
Returns this Long with bits shifted to the right by the given amount, with
the new top bits matching the current sign bit.
@param {number} numBits The number of bits by which to shift.
@return {!goog.math.Long} This shifted to the right by the given amount, with
    zeros placed into the new leading bits.