log2.hpp

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/*################################################################################
  ##
  ##   Copyright (C) 2016-2023 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.
  ##
  ################################################################################*/
 
/*
 * compile-time binary logarithm function
 */
 
#ifndef _gcem_log2_HPP
#define _gcem_log2_HPP
 
#include <cmath>
#include <type_traits>
 
namespace gcem
{
 
namespace internal
{
 
template<typename T>
constexpr
return_t<T>
log2_check(const T x)
noexcept
{
    // log_2(x) = ln(x) / ln(2)
    return return_t<T>(log(x) / GCEM_LOG_2);
}
 
}
 
/**
 * Compile-time binary logarithm function
 *
 * @param x a real-valued input.
 * @return \f$ \log_2(x) \f$ using \f[ \log_{2}(x) = \frac{\log_e(x)}{\log_e(2)} \f] 
 */
 
template<typename T>
constexpr
return_t<T>
log2(const T x)
noexcept
{
  if (std::is_constant_evaluated()) {
    return internal::log2_check( x );
  } else {
    return std::log2(x);
  }
}
 
}
 
#endif