module.exports = calculateW

/**
 * Calculates the W component of a quat from the X, Y, and Z components.
 * Assumes that quaternion is 1 unit in length.
 * Any existing W component will be ignored.
 *
 * @param {quat} out the receiving quaternion
 * @param {quat} a quat to calculate W component of
 * @returns {quat} out
 */
function calculateW (out, a) {
  var x = a[0], y = a[1], z = a[2]

  out[0] = x
  out[1] = y
  out[2] = z
  out[3] = Math.sqrt(Math.abs(1.0 - x * x - y * y - z * z))
  return out
}