precision.hpp

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/*
  Copyright (C) 2017 Marcus N Campbell Bannerman <[email protected]>

  This file is part of stator.

  stator 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.

  stator 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 stator. If not, see <http://www.gnu.org/licenses/>.
*/

#pragma once
#include <cstddef>
#include <cstdlib>
#include <cmath>
#include <limits>
#include <type_traits>

namespace sym {
  template<class T>
  size_t subtraction_precision(const T f1, const T f2) {
    static_assert(std::is_floating_point<T>(), "Can only calculate the precision of addition between floating point types");
    
    //Catch the case where this is not actually a subtraction at all
    if ((f1 == 0) || (f2 == 0) || (std::signbit(f1) != std::signbit(f2)))
    return std::numeric_limits<size_t>::max();
    
    int exp1, exp2;
    std::frexp(f1, &exp1);
    std::frexp(f2, &exp2);
    return std::abs(exp1-exp2);
  }

  template<class T>
  size_t addition_precision(const T f1, const T f2) {
    return subtraction_precision(f1, -f2);
  }
  
}