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// Copyright (c) 2008 Max-Planck-Institute Saarbruecken (Germany).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org); you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public License as
// published by the Free Software Foundation; version 2.1 of the License.
// See the file LICENSE.LGPL distributed with CGAL.
//
// Licensees holding a valid commercial license may use this file in
// accordance with the commercial license agreement provided with the software.
//
// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
//
// $URL: svn+ssh://scm.gforge.inria.fr/svn/cgal/branches/CGAL-3.6-branch/Algebraic_foundations/include/CGAL/ipower.h $
// $Id: ipower.h 52628 2009-10-20 08:59:26Z lrineau $
//
//
// Author(s) : Michael Hemmer
//
// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
//
// $URL: svn+ssh://scm.gforge.inria.fr/svn/cgal/branches/CGAL-3.6-branch/Algebraic_foundations/include/CGAL/ipower.h $
#ifndef CGAL_IPOWER_H
#define CGAL_IPOWER_H
CGAL_BEGIN_NAMESPACE
template <typename NT>
inline
NT ipower(const NT& base, int expn) {
// compute base^expn using square-and-multiply
CGAL_precondition(expn >= 0);
// handle trivial cases efficiently
if (expn == 0) return NT(1);
if (expn == 1) return base;
// find the most significant non-zero bit of expn
int e = expn, msb = 0;
while (e >>= 1) msb++;
// computing base^expn by square-and-multiply
NT res = base;
int b = 1<<msb;
while (b >>= 1) { // is there another bit right of what we saw so far?
res *= res;
if (expn & b) res *= base;
}
return res;
}
template <typename NT>
inline
NT ipower(const NT& base, long expn) {
// compute base^expn using square-and-multiply
CGAL_precondition(expn >= 0);
// handle trivial cases efficiently
if (expn == 0) return NT(1);
if (expn == 1) return base;
// find the most significant non-zero bit of expn
int e = expn, msb = 0;
while (e >>= 1) msb++;
// computing base^expn by square-and-multiply
NT res = base;
int b = 1<<msb;
while (b >>= 1) { // is there another bit right of what we saw so far?
res *= res;
if (expn & b) res *= base;
}
return res;
}
CGAL_END_NAMESPACE
#endif // CGAL_IPOWER_H
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