partial(len, x, _end) {
			if (len === 32) {
				return x;
			}
			return (_end ? x | 0 : x << (32 - len)) + len * 0x10000000000;
		}
Make a partial word for a bit array.
@param {Number} len The number of bits in the word.
@param {Number} x The bits.
@param {Number} [_end=0] Pass 1 if x has already been shifted to the high side.
@return {Number} The partial word.