power.hpp

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//****************************************************************************//
//     Copyright (C) 2016-2024 Florent Hivert <Florent.Hivert@lisn.fr>,       //
//                                                                            //
//  This file is part of HP-Combi <https://github.com/libsemigroups/HPCombi>  //
//                                                                            //
//  HP-Combi is free software: you can redistribute it and/or modify it       //
//  under the terms of the GNU General Public License as published by the     //
//  Free Software Foundation, either version 3 of the License, or             //
//  (at your option) any later version.                                       //
//                                                                            //
//  HP-Combi is distributed in the hope that it will be useful, but WITHOUT   //
//  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or     //
//  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License      //
//  for  more details.                                                        //
//                                                                            //
//  You should have received a copy of the GNU General Public License along   //
//  with HP-Combi. If not, see <https://www.gnu.org/licenses/>.               //
//****************************************************************************//
 
#ifndef HPCOMBI_POWER_HPP_
#define HPCOMBI_POWER_HPP_
 
namespace HPCombi {
 
namespace power_helper {
 
// Forward declaration
template <typename T> struct Monoid;
 
}  // namespace power_helper
 
template <typename T, typename M = power_helper::Monoid<T>>
const T square(const T x) {
    return M::prod(x, x);
}
 
template <unsigned exp, typename T, typename M = power_helper::Monoid<T>>
const T pow(const T x) {
    return (exp == 0) ? M::one()
           : (exp % 2 == 0)
               ? square<T, M>(pow<unsigned(exp / 2), T, M>(x))
               : M::prod(x, square<T, M>(pow<unsigned(exp / 2), T, M>(x)));
}
 
namespace power_helper {
 
template <typename T> struct Monoid {
    static const T one() { return 1; }
 
    static const T prod(T a, T b) { return a * b; }
};
 
}  // namespace power_helper
 
}  // namespace HPCombi
 
#endif  // HPCOMBI_POWER_HPP_