bitLength(a) {
			const l = a.length;
			if (l === 0) {
				return 0;
			}
			const x = a[l - 1];
			return (l - 1) * 32 + bitArray.getPartial(x);
		}
Find the length of an array of bits.
@param {bitArray} a The array.
@return {Number} The length of a, in bits.