text: 
  #ifndef QUATERNION_H_
  #define QUATERNION_H_
  
  // quaternion.h
  //
  // Copyright (c) 2015 Iwe Labs
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included in
  // all copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  // THE SOFTWARE.
  
  #include <math.h>
  #include "datatypes.h"
  
  struct Vector;
  
  struct Quaternion {
      Quaternion();
      Quaternion(FLOAT a, FLOAT b, FLOAT c, FLOAT d);
      Quaternion(const Quaternion& q);
      Quaternion(const Vector& axis, FLOAT theta);
      explicit Quaternion(const Vector& v);
  
      void conjugate();
      void multiply(const Quaternion& q);
      
      FLOAT norm() const;
      FLOAT getPitch() const;
      FLOAT getYaw() const;
      FLOAT getRoll() const;
      bool equals(const Quaternion& q) const;
  	
  	FLOAT x;
  	FLOAT y;
  	FLOAT z;
  	FLOAT w;
  };
  
  #endif /*QUATERNION_H_*/
  