76 lines
2.0 KiB
C
76 lines
2.0 KiB
C
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// Copyright (c) 2008 Max-Planck-Institute Saarbruecken (Germany).
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// All rights reserved.
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//
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// This file is part of CGAL (www.cgal.org)
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//
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// $URL: https://github.com/CGAL/cgal/blob/v5.1/Algebraic_foundations/include/CGAL/ipower.h $
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// $Id: ipower.h 0779373 2020-03-26T13:31:46+01:00 Sébastien Loriot
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// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
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//
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//
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// Author(s) : Michael Hemmer
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//
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// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
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// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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//
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// $URL: https://github.com/CGAL/cgal/blob/v5.1/Algebraic_foundations/include/CGAL/ipower.h $
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#ifndef CGAL_IPOWER_H
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#define CGAL_IPOWER_H
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#include <CGAL/assertions.h>
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namespace CGAL {
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template <typename NT>
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inline
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NT ipower(const NT& base, int expn) {
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// compute base^expn using square-and-multiply
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CGAL_precondition(expn >= 0);
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// handle trivial cases efficiently
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if (expn == 0) return NT(1);
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if (expn == 1) return base;
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// find the most significant non-zero bit of expn
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int e = expn, msb = 0;
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while (e >>= 1) msb++;
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// computing base^expn by square-and-multiply
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NT res = base;
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int b = 1<<msb;
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while (b >>= 1) { // is there another bit right of what we saw so far?
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res *= res;
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if (expn & b) res *= base;
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}
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return res;
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}
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template <typename NT>
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inline
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NT ipower(const NT& base, long expn) {
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// compute base^expn using square-and-multiply
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CGAL_precondition(expn >= 0);
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// handle trivial cases efficiently
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if (expn == 0) return NT(1);
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if (expn == 1) return base;
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// find the most significant non-zero bit of expn
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long e = expn, msb = 0;
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while (e >>= 1) msb++;
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// computing base^expn by square-and-multiply
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NT res = base;
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long b = 1L<<msb;
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while (b >>= 1) { // is there another bit right of what we saw so far?
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res *= res;
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if (expn & b) res *= base;
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}
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return res;
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}
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} //namespace CGAL
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#endif // CGAL_IPOWER_H
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