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diff --git a/extern/bullet2/BulletCollision/CollisionDispatch/btUnionFind.h b/extern/bullet2/BulletCollision/CollisionDispatch/btUnionFind.h
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+/*
+Bullet Continuous Collision Detection and Physics Library
+Copyright (c) 2003-2006 Erwin Coumans  http://continuousphysics.com/Bullet/
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose, 
+including commercial applications, and to alter it and redistribute it freely, 
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef UNION_FIND_H
+#define UNION_FIND_H
+
+#include "LinearMath/btAlignedObjectArray.h"
+
+	#define USE_PATH_COMPRESSION 1
+
+struct	btElement
+{
+	int	m_id;
+	int	m_sz;
+};
+
+///UnionFind calculates connected subsets
+// Implements weighted Quick Union with path compression
+// optimization: could use short ints instead of ints (halving memory, would limit the number of rigid bodies to 64k, sounds reasonable)
+class btUnionFind
+  {
+    private:
+		btAlignedObjectArray<btElement>	m_elements;
+
+    public:
+	  
+		btUnionFind();
+		~btUnionFind();
+
+	
+		//this is a special operation, destroying the content of btUnionFind.
+		//it sorts the elements, based on island id, in order to make it easy to iterate over islands
+		void	sortIslands();
+
+	  void	reset(int N);
+
+	  SIMD_FORCE_INLINE int	getNumElements() const
+	  {
+		  return int(m_elements.size());
+	  }
+	  SIMD_FORCE_INLINE bool  isRoot(int x) const
+	  {
+		  return (x == m_elements[x].m_id);
+	  }
+
+	  btElement&	getElement(int index)
+	  {
+		  return m_elements[index];
+	  }
+	  const btElement& getElement(int index) const
+	  {
+		  return m_elements[index];
+	  }
+   
+	  void	allocate(int N);
+	  void	Free();
+
+
+
+
+	  int find(int p, int q)
+		{ 
+			return (find(p) == find(q)); 
+		}
+
+		void unite(int p, int q)
+		{
+			int i = find(p), j = find(q);
+			if (i == j) 
+				return;
+
+#ifndef USE_PATH_COMPRESSION
+			//weighted quick union, this keeps the 'trees' balanced, and keeps performance of unite O( log(n) )
+			if (m_elements[i].m_sz < m_elements[j].m_sz)
+			{ 
+				m_elements[i].m_id = j; m_elements[j].m_sz += m_elements[i].m_sz; 
+			}
+			else 
+			{ 
+				m_elements[j].m_id = i; m_elements[i].m_sz += m_elements[j].m_sz; 
+			}
+#else
+			m_elements[i].m_id = j; m_elements[j].m_sz += m_elements[i].m_sz; 
+#endif //USE_PATH_COMPRESSION
+		}
+
+		int find(int x)
+		{ 
+			//btAssert(x < m_N);
+			//btAssert(x >= 0);
+
+			while (x != m_elements[x].m_id) 
+			{
+		//not really a reason not to use path compression, and it flattens the trees/improves find performance dramatically
+	
+		#ifdef USE_PATH_COMPRESSION
+				const btElement* elementPtr = &m_elements[m_elements[x].m_id];
+				m_elements[x].m_id = elementPtr->m_id;
+				x = elementPtr->m_id;			
+		#else//
+				x = m_elements[x].m_id;
+		#endif		
+				//btAssert(x < m_N);
+				//btAssert(x >= 0);
+
+			}
+			return x; 
+		}
+
+
+  };
+
+
+#endif //UNION_FIND_H