module.exports = rotate

/**
 * Rotates a mat3 by the given angle
 *
 * @alias mat3.rotate
 * @param {mat3} out the receiving matrix
 * @param {mat3} a the matrix to rotate
 * @param {Number} rad the angle to rotate the matrix by
 * @returns {mat3} out
 */
function rotate(out, a, rad) {
  var a00 = a[0], a01 = a[1], a02 = a[2]
  var a10 = a[3], a11 = a[4], a12 = a[5]
  var a20 = a[6], a21 = a[7], a22 = a[8]

  var s = Math.sin(rad)
  var c = Math.cos(rad)

  out[0] = c * a00 + s * a10
  out[1] = c * a01 + s * a11
  out[2] = c * a02 + s * a12

  out[3] = c * a10 - s * a00
  out[4] = c * a11 - s * a01
  out[5] = c * a12 - s * a02

  out[6] = a20
  out[7] = a21
  out[8] = a22

  return out
}