module.exports = invert

/**
 * Calculates the inverse of a quat
 *
 * @param {quat} out the receiving quaternion
 * @param {quat} a quat to calculate inverse of
 * @returns {quat} out
 */
function invert (out, a) {
  var a0 = a[0], a1 = a[1], a2 = a[2], a3 = a[3],
    dot = a0 * a0 + a1 * a1 + a2 * a2 + a3 * a3,
    invDot = dot ? 1.0 / dot : 0

  // TODO: Would be faster to return [0,0,0,0] immediately if dot == 0

  out[0] = -a0 * invDot
  out[1] = -a1 * invDot
  out[2] = -a2 * invDot
  out[3] = a3 * invDot
  return out
}