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89 lines
2.3 KiB
C++
89 lines
2.3 KiB
C++
/*
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Copyright (c) Marshall Clow 2014.
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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Revision history:
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2 Dec 2014 mtc First version; power
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*/
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/// \file algorithm.hpp
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/// \brief Misc Algorithms
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/// \author Marshall Clow
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///
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#ifndef BOOST_ALGORITHM_HPP
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#define BOOST_ALGORITHM_HPP
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#include <functional> // for plus and multiplies
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#include <boost/utility/enable_if.hpp> // for boost::disable_if
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#include <boost/type_traits/is_integral.hpp>
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namespace boost { namespace algorithm {
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template <typename T>
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T identity_operation ( std::multiplies<T> ) { return T(1); }
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template <typename T>
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T identity_operation ( std::plus<T> ) { return T(0); }
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/// \fn power ( T x, Integer n )
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/// \return the value "x" raised to the power "n"
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///
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/// \param x The value to be exponentiated
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/// \param n The exponent (must be >= 0)
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///
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// \remark Taken from Knuth, The Art of Computer Programming, Volume 2:
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// Seminumerical Algorithms, Section 4.6.3
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template <typename T, typename Integer>
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typename boost::enable_if<boost::is_integral<Integer>, T>::type
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power (T x, Integer n) {
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T y = 1; // Should be "T y{1};"
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if (n == 0) return y;
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while (true) {
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if (n % 2 == 1) {
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y = x * y;
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if (n == 1)
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return y;
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}
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n = n / 2;
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x = x * x;
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}
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return y;
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}
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/// \fn power ( T x, Integer n, Operation op )
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/// \return the value "x" raised to the power "n"
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/// using the operation "op".
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///
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/// \param x The value to be exponentiated
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/// \param n The exponent (must be >= 0)
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/// \param op The operation used
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///
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// \remark Taken from Knuth, The Art of Computer Programming, Volume 2:
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// Seminumerical Algorithms, Section 4.6.3
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template <typename T, typename Integer, typename Operation>
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typename boost::enable_if<boost::is_integral<Integer>, T>::type
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power (T x, Integer n, Operation op) {
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T y = identity_operation(op);
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if (n == 0) return y;
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while (true) {
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if (n % 2 == 1) {
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y = op(x, y);
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if (n == 1)
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return y;
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}
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n = n / 2;
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x = op(x, x);
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}
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return y;
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}
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}}
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#endif // BOOST_ALGORITHM_HPP
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