aureooms/js-uint64

/**
 * Right rotate a 64-bit unsigned integer given as a pair of two 32-bit signed
 * integers in big endian order.
 *
 * NB: used in the sha2 family
 *
 * @param {Array} a
 * @param {Number} s `0 <= s <= 64`
 * @returns {Array}
 */

export function rotr64(a, s) {
    if (s === 0 || s === 64) {
        return [a[0], a[1]];
    }

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

    if (s === 32) {
        return [a[1], a[0]];
    }

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