find_exponent.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 find_exponent function
 */
 
#ifndef _gcem_find_exponent_HPP
#define _gcem_find_exponent_HPP
 
namespace gcem
{
 
namespace internal
{
 
template<typename T>
constexpr
llint_t
find_exponent(const T x, const llint_t exponent)
noexcept
{
    return( // < 1
            x < T(1e-03)  ? \
                find_exponent(x * T(1e+04), exponent - llint_t(4)) :
            x < T(1e-01)  ? \
                find_exponent(x * T(1e+02), exponent - llint_t(2)) :
            x < T(1)  ? \
                find_exponent(x * T(10), exponent - llint_t(1)) :
            // > 10
            x > T(10) ? \
                find_exponent(x / T(10), exponent + llint_t(1)) :
            x > T(1e+02) ? \
                find_exponent(x / T(1e+02), exponent + llint_t(2)) :
            x > T(1e+04) ? \
                find_exponent(x / T(1e+04), exponent + llint_t(4)) :
            // else
                exponent );
}
 
}
 
}
 
#endif