module.exports = transformQuat

/**
 * Transforms the vec4 with a quat
 *
 * @param {vec4} out the receiving vector
 * @param {vec4} a the vector to transform
 * @param {quat} q quaternion to transform with
 * @returns {vec4} out
 */
function transformQuat (out, a, q) {
  var x = a[0], y = a[1], z = a[2],
    qx = q[0], qy = q[1], qz = q[2], qw = q[3],

    // calculate quat * vec
    ix = qw * x + qy * z - qz * y,
    iy = qw * y + qz * x - qx * z,
    iz = qw * z + qx * y - qy * x,
    iw = -qx * x - qy * y - qz * z

  // calculate result * inverse quat
  out[0] = ix * qw + iw * -qx + iy * -qz - iz * -qy
  out[1] = iy * qw + iw * -qy + iz * -qx - ix * -qz
  out[2] = iz * qw + iw * -qz + ix * -qy - iy * -qx
  out[3] = a[3]
  return out
}