aureooms/js-uint64

/**
 * Left shift a 64-bit unsigned integer given as a pair of two 32-bit signed
 * integers in big endian order.
 *
 * @param {Array} a
 * @param {Number} s `s >= 0`
 * @returns {Array}
 */
export function shl64(a, s) {
    if (s === 0) {
        return [a[0], a[1]];
    }

    if (s < 32) {
        return [(a[1] >>> (32 - s)) | (a[0] << s), (a[1] << s) | 0];
    }

    if (s < 64) {
        return [(a[1] << (s - 32)) | 0, 0];
    }

    return [a[0], a[1]];
}