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// Copyright (c) 2008 Max-Planck-Institute Saarbruecken (Germany).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL: https://github.com/CGAL/cgal/blob/v6.1/Algebraic_foundations/include/CGAL/ipower.h $
// $Id: include/CGAL/ipower.h b26b07a1242 $
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
//
// 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: https://github.com/CGAL/cgal/blob/v6.1/Algebraic_foundations/include/CGAL/ipower.h $
#ifndef CGAL_IPOWER_H
#define CGAL_IPOWER_H
#include <CGAL/assertions.h>
namespace CGAL {
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
long e = expn, msb = 0;
while (e >>= 1) msb++;
// computing base^expn by square-and-multiply
NT res = base;
long b = 1L<<msb;
while (b >>= 1) { // is there another bit right of what we saw so far?
res *= res;
if (expn & b) res *= base;
}
return res;
}
} //namespace CGAL
#endif // CGAL_IPOWER_H
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