different quat2eul function from the internet

MshViewer/Source/Object.cpp

@@ -574,21 +574,20 @@ void Object::readUV(Segment* dataDestination, std::streampos position)
 
 void Object::quat2eul(float &quat0, float &quat1, float & quat2, float &quat3)
 {
-	float eulX = atan2(
-					2 * (quat0 * quat1 + quat2 * quat3),
-					1 - 2 * (pow(quat1, 2) + pow(quat2, 2))
-				 );
+	float ysqr = quat1 * quat1;
+	float t0 = -2.0f * (ysqr + quat2 * quat2) + 1.0f;
+	float t1 = +2.0f * (quat0 * quat1 - quat3 * quat2);
+	float t2 = -2.0f * (quat0 * quat2 + quat3 * quat1);
+	float t3 = +2.0f * (quat1 * quat2 - quat3 * quat0);
+	float t4 = -2.0f * (quat0 * quat0 + ysqr) + 1.0f;
 
-	float eulY = asin(2 * (quat0 * quat2 - quat3 * quat1));
+	t2 = t2 > 1.0f ? 1.0f : t2;
+	t2 = t2 < -1.0f ? -1.0f : t2;
 
-	float eulZ = atan2(
-		2 * (quat0 * quat3 + quat1 * quat2),
-		1 - 2 * (pow(quat2, 2) + pow(quat3, 2))
-	) - PI;
+	quat1 = std::asin(t2);
+	quat0 = std::atan2(t3, t4);
+	quat2 = std::atan2(t1, t0);
 
-	quat0 = eulX;
-	quat1 = eulY;
-	quat2 = eulZ;
 }