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// Copyright 2019 Hans Dembinski
//
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt
// or copy at http://www.boost.org/LICENSE_1_0.txt)
#ifndef BOOST_HISTOGRAM_DETAIL_SAFE_COMPARISON_HPP
#define BOOST_HISTOGRAM_DETAIL_SAFE_COMPARISON_HPP
#include <boost/mp11/utility.hpp>
#include <boost/type.hpp>
#include <type_traits>
namespace boost {
namespace histogram {
namespace detail {
template <class T>
auto make_unsigned(const T& t) noexcept {
static_assert(std::is_integral<T>::value, "");
return static_cast<std::make_unsigned_t<T>>(t);
}
template <class T>
using number_category =
mp11::mp_if<std::is_integral<T>,
mp11::mp_if<std::is_signed<T>, type<int>, type<unsigned>>, type<void>>;
// version of std::equal_to<> which handles signed and unsigned integers correctly
struct safe_equal {
template <class T, class U>
bool operator()(const T& t, const U& u) const noexcept {
return impl(number_category<T>{}, number_category<U>{}, t, u);
}
template <class C1, class C2, class T, class U>
bool impl(C1, C2, const T& t, const U& u) const noexcept {
return t == u;
}
template <class T, class U>
bool impl(type<int>, type<unsigned>, const T& t, const U& u) const noexcept {
return t >= 0 && make_unsigned(t) == u;
}
template <class T, class U>
bool impl(type<unsigned>, type<int>, const T& t, const U& u) const noexcept {
return impl(type<int>{}, type<unsigned>{}, u, t);
}
};
// version of std::less<> which handles signed and unsigned integers correctly
struct safe_less {
template <class T, class U>
bool operator()(const T& t, const U& u) const noexcept {
return impl(number_category<T>{}, number_category<U>{}, t, u);
}
template <class C1, class C2, class T, class U>
bool impl(C1, C2, const T& t, const U& u) const noexcept {
return t < u;
}
template <class T, class U>
bool impl(type<int>, type<unsigned>, const T& t, const U& u) const noexcept {
return t < 0 || make_unsigned(t) < u;
}
template <class T, class U>
bool impl(type<unsigned>, type<int>, const T& t, const U& u) const noexcept {
return 0 < u && t < make_unsigned(u);
}
};
// version of std::greater<> which handles signed and unsigned integers correctly
struct safe_greater {
template <class T, class U>
bool operator()(const T& t, const U& u) const noexcept {
return safe_less()(u, t);
}
};
} // namespace detail
} // namespace histogram
} // namespace boost
#endif
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