diff options
Diffstat (limited to 'libstdc++-v3/include/std/numeric')
| -rw-r--r-- | libstdc++-v3/include/std/numeric | 75 |
1 files changed, 42 insertions, 33 deletions
diff --git a/libstdc++-v3/include/std/numeric b/libstdc++-v3/include/std/numeric index 5388239ef04..60a99d18ffd 100644 --- a/libstdc++-v3/include/std/numeric +++ b/libstdc++-v3/include/std/numeric @@ -68,6 +68,7 @@ #if __cplusplus >= 201402L # include <type_traits> # include <bit> +# include <ext/numeric_traits.h> #endif #if __cplusplus >= 201703L @@ -93,19 +94,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION #if __cplusplus >= 201402L namespace __detail { - // std::abs is not constexpr, doesn't support unsigned integers, - // and std::abs(std::numeric_limits<T>::min()) is undefined. - template<typename _Up, typename _Tp> - constexpr _Up - __absu(_Tp __val) + // Like std::abs, but supports unsigned types and returns the specified type, + // so |std::numeric_limits<_Tp>::min()| is OK if representable in _Res. + template<typename _Res, typename _Tp> + constexpr _Res + __abs_r(_Tp __val) { - static_assert(is_unsigned<_Up>::value, "result type must be unsigned"); - static_assert(sizeof(_Up) >= sizeof(_Tp), + static_assert(sizeof(_Res) >= sizeof(_Tp), "result type must be at least as wide as the input type"); - return __val < 0 ? -(_Up)__val : (_Up)__val; + + if (__val >= 0) + return __val; +#ifdef _GLIBCXX_ASSERTIONS + if (!__is_constant_evaluated()) // overflow already detected in constexpr + __glibcxx_assert(__val != __gnu_cxx::__int_traits<_Res>::__min); +#endif + return -static_cast<_Res>(__val); } - template<typename _Up> void __absu(bool) = delete; + template<typename> void __abs_r(bool) = delete; // GCD implementation, using Stein's algorithm template<typename _Tp> @@ -142,16 +149,6 @@ namespace __detail __n >>= std::__countr_zero(__n); } } - - // LCM implementation - template<typename _Tp> - constexpr _Tp - __lcm(_Tp __m, _Tp __n) - { - return (__m != 0 && __n != 0) - ? (__m / __detail::__gcd(__m, __n)) * __n - : 0; - } } // namespace __detail #if __cplusplus >= 201703L @@ -166,13 +163,14 @@ namespace __detail constexpr common_type_t<_Mn, _Nn> gcd(_Mn __m, _Nn __n) noexcept { - static_assert(is_integral_v<_Mn>, "std::gcd arguments must be integers"); - static_assert(is_integral_v<_Nn>, "std::gcd arguments must be integers"); - static_assert(_Mn(2) != _Mn(1), "std::gcd arguments must not be bool"); - static_assert(_Nn(2) != _Nn(1), "std::gcd arguments must not be bool"); - using _Up = make_unsigned_t<common_type_t<_Mn, _Nn>>; - return __detail::__gcd(__detail::__absu<_Up>(__m), - __detail::__absu<_Up>(__n)); + static_assert(is_integral_v<_Mn> && is_integral_v<_Nn>, + "std::gcd arguments must be integers"); + static_assert(_Mn(2) == 2 && _Nn(2) == 2, + "std::gcd arguments must not be bool"); + using _Ct = common_type_t<_Mn, _Nn>; + const _Ct __m2 = __detail::__abs_r<_Ct>(__m); + const _Ct __n2 = __detail::__abs_r<_Ct>(__n); + return __detail::__gcd<make_unsigned_t<_Ct>>(__m2, __n2); } /// Least common multiple @@ -180,13 +178,24 @@ namespace __detail constexpr common_type_t<_Mn, _Nn> lcm(_Mn __m, _Nn __n) noexcept { - static_assert(is_integral_v<_Mn>, "std::lcm arguments must be integers"); - static_assert(is_integral_v<_Nn>, "std::lcm arguments must be integers"); - static_assert(_Mn(2) == 2, "std::lcm arguments must not be bool"); - static_assert(_Nn(2) == 2, "std::lcm arguments must not be bool"); - using _Up = make_unsigned_t<common_type_t<_Mn, _Nn>>; - return __detail::__lcm(__detail::__absu<_Up>(__m), - __detail::__absu<_Up>(__n)); + static_assert(is_integral_v<_Mn> && is_integral_v<_Nn>, + "std::lcm arguments must be integers"); + static_assert(_Mn(2) == 2 && _Nn(2) == 2, + "std::lcm arguments must not be bool"); + using _Ct = common_type_t<_Mn, _Nn>; + const _Ct __m2 = __detail::__abs_r<_Ct>(__m); + const _Ct __n2 = __detail::__abs_r<_Ct>(__n); + if (__m2 == 0 || __n2 == 0) + return 0; + _Ct __r = __m2 / __detail::__gcd<make_unsigned_t<_Ct>>(__m2, __n2); + + if constexpr (is_signed_v<_Ct>) + if (__is_constant_evaluated()) + return __r * __n2; // constant evaluation can detect overflow here. + + bool __overflow = __builtin_mul_overflow(__r, __n2, &__r); + __glibcxx_assert(!__overflow); + return __r; } #endif // C++17 |