function rotateZ$1(out, a, rad) {
    rad *= 0.5;
    var ax = a[0],
        ay = a[1],
        az = a[2],
        aw = a[3];
    var bz = Math.sin(rad),
        bw = Math.cos(rad);
    out[0] = ax * bw + ay * bz;
    out[1] = ay * bw - ax * bz;
    out[2] = az * bw + aw * bz;
    out[3] = aw * bw - az * bz;
    return out;
  }
Rotates a quaternion by the given angle about the Z axis

@param {quat} out quat receiving operation result
@param {ReadonlyQuat} a quat to rotate
@param {number} rad angle (in radians) to rotate
@returns {quat} out