97 lines
2.9 KiB
C++
97 lines
2.9 KiB
C++
// Copyright 2023 Matt Borland
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// Distributed under the Boost Software License, Version 1.0.
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// https://www.boost.org/LICENSE_1_0.txt
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#ifndef BOOST_CHARCONV_LIMITS_HPP
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#define BOOST_CHARCONV_LIMITS_HPP
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#include <boost/charconv/detail/config.hpp>
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#include <limits>
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#include <type_traits>
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namespace boost { namespace charconv {
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// limits<T>::max_chars10: the minimum size of the buffer that needs to be
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// passed to to_chars to guarantee successful conversion for all values of
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// type T, when either no base is passed, or base 10 is passed
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//
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// limits<T>::max_chars: the minimum size of the buffer that needs to be
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// passed to to_chars to guarantee successful conversion for all values of
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// type T, for any value of base
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namespace detail
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{
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constexpr int exp_digits( int exp )
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{
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return exp < 100? 2: exp < 1000? 3: exp < 10000? 4: 5;
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}
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#if defined(BOOST_HAS_INT128)
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template<class T> struct is_int128: std::is_same<T, boost::int128_type> {};
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template<class T> struct is_uint128: std::is_same<T, boost::int128_type> {};
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#else
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template<class T> struct is_int128: std::false_type {};
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template<class T> struct is_uint128: std::false_type {};
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#endif
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} // namespace detail
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template<typename T> struct limits
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{
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BOOST_ATTRIBUTE_UNUSED static constexpr int max_chars10 =
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// int128_t
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detail::is_int128<T>::value? 38+2: // digits10 + 1 + sign
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// uint128_t
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detail::is_uint128<T>::value? 38+1: // digits10 + 1
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// integral
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std::numeric_limits<T>::is_integer? std::numeric_limits<T>::digits10 + 1 + std::numeric_limits<T>::is_signed:
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// floating point
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std::numeric_limits<T>::max_digits10 + 3 + 2 + detail::exp_digits( std::numeric_limits<T>::max_exponent10 ); // -1.(max_digits10)e+(max_exp)
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BOOST_ATTRIBUTE_UNUSED static constexpr int max_chars =
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// int128_t
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detail::is_int128<T>::value? 127+2: // digits + 1 + sign
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// uint128_t
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detail::is_uint128<T>::value? 128+1: // digits + 1
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// integral
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std::numeric_limits<T>::is_integer? std::numeric_limits<T>::digits + 1 + std::numeric_limits<T>::is_signed:
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// floating point
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std::numeric_limits<T>::max_digits10 + 3 + 2 + detail::exp_digits( std::numeric_limits<T>::max_exponent10 ); // as above
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};
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#if defined(BOOST_CHARCONV_HAS_QUADMATH)
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template <> struct limits<__float128>
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{
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BOOST_ATTRIBUTE_UNUSED static constexpr int max_chars10 = 33 + 3 + 2 + 5;
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BOOST_ATTRIBUTE_UNUSED static constexpr int max_chars = max_chars10;
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};
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#endif
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#if defined(BOOST_NO_CXX17_INLINE_VARIABLES)
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// Definitions of in-class constexpr members are allowed but deprecated in C++17
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template<typename T> BOOST_ATTRIBUTE_UNUSED constexpr int limits<T>::max_chars10;
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template<typename T> BOOST_ATTRIBUTE_UNUSED constexpr int limits<T>::max_chars;
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#endif // defined(BOOST_NO_CXX17_INLINE_VARIABLES)
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}} // namespace boost::charconv
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#endif // BOOST_CHARCONV_LIMITS_HPP
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