lcm.hpp

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/*################################################################################
  ##
  ##   Copyright (C) 2016-2022 Keith O'Hara
  ##
  ##   This file is part of the GCE-Math C++ library.
  ##
  ##   Licensed under the Apache License, Version 2.0 (the "License");
  ##   you may not use this file except in compliance with the License.
  ##   You may obtain a copy of the License at
  ##
  ##       http://www.apache.org/licenses/LICENSE-2.0
  ##
  ##   Unless required by applicable law or agreed to in writing, software
  ##   distributed under the License is distributed on an "AS IS" BASIS,
  ##   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ##   See the License for the specific language governing permissions and
  ##   limitations under the License.
  ##
  ################################################################################*/
 
#ifndef _gcem_lcm_HPP
#define _gcem_lcm_HPP
 
namespace internal
{
 
template<typename T>
constexpr
T
lcm_compute(const T a, const T b)
noexcept
{
    return abs(a * (b / gcd(a,b)));
}
 
template<typename T1, typename T2, typename TC = common_t<T1,T2>>
constexpr
TC
lcm_type_check(const T1 a, const T2 b)
noexcept
{
    return lcm_compute(static_cast<TC>(a),static_cast<TC>(b));
}
 
}
 
/**
 * Compile-time least common multiple (LCM) function
 *
 * @param a integral-valued input.
 * @param b integral-valued input.
 * @return the least common multiple between integers \c a and \c b using the representation \f[ \text{lcm}(a,b) = \dfrac{| a b |}{\text{gcd}(a,b)} \f]
 * where \f$ \text{gcd}(a,b) \f$ denotes the greatest common divisor between \f$ a \f$ and \f$ b \f$.
 */
 
template<typename T1, typename T2>
constexpr
common_t<T1,T2>
lcm(const T1 a, const T2 b)
noexcept
{
    return internal::lcm_type_check(a,b);
}
 
#endif