Function atan2

Source/astcenc_vecmathlib.h:301–306

* @brief Return fast, but approximate, vector atan2(x, y). */

 * @brief Return fast, but approximate, vector atan2(x, y).
 */
ASTCENC_SIMD_INLINE vfloat atan2(vfloat y, vfloat x)
{
	vfloat z = atan(abs(y / x));
	vmask xmask = x < vfloat::zero();
	return change_sign(select(z, vfloat(astc::PI) - z, xmask), y);
}

/*
 * @brief Factory that returns a unit length 4 component vfloat4.