module.exports = multiply

/**
 * Multiplies two quat's
 *
 * @param {quat} out the receiving quaternion
 * @param {quat} a the first operand
 * @param {quat} b the second operand
 * @returns {quat} out
 */
function multiply (out, a, b) {
  var ax = a[0], ay = a[1], az = a[2], aw = a[3],
    bx = b[0], by = b[1], bz = b[2], bw = b[3]

  out[0] = ax * bw + aw * bx + ay * bz - az * by
  out[1] = ay * bw + aw * by + az * bx - ax * bz
  out[2] = az * bw + aw * bz + ax * by - ay * bx
  out[3] = aw * bw - ax * bx - ay * by - az * bz
  return out
}