src/rotr64.js

/**
 * 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)];
}