long-double

Author: izvolov

libcxx/include/__algorithm/radix_sort.h

@@ -31,7 +31,6 @@
 #include <__algorithm/move.h>
 #include <__bit/bit_cast.h>
 #include <__bit/bit_log2.h>
-#include <__bit/countl.h>
 #include <__config>
 #include <__cstddef/size_t.h>
 #include <__functional/identity.h>
@@ -44,12 +43,15 @@
 #include <__numeric/partial_sum.h>
 #include <__type_traits/decay.h>
 #include <__type_traits/enable_if.h>
+#include <__type_traits/integral_constant.h>
 #include <__type_traits/invoke.h>
 #include <__type_traits/is_assignable.h>
 #include <__type_traits/is_enum.h>
 #include <__type_traits/is_integral.h>
 #include <__type_traits/is_unsigned.h>
 #include <__type_traits/make_unsigned.h>
+#include <__type_traits/void_t.h>
+#include <__utility/declval.h>
 #include <__utility/forward.h>
 #include <__utility/integer_sequence.h>
 #include <__utility/move.h>
@@ -379,6 +381,20 @@ _LIBCPP_HIDE_FROM_ABI constexpr auto __to_ordered_integral(_Floating __f) {
 template <class _Enum, enable_if_t< is_enum<_Enum>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI constexpr auto __to_ordered_integral(_Enum __e) = delete;
 
+// `long double` varies significantly across platforms and compilers, making it practically
+// impossible to determine its actual bit width for conversion to an ordered integer.
+inline _LIBCPP_HIDE_FROM_ABI constexpr auto __to_ordered_integral(long double) = delete;
+
+template <class _Tp, class = void>
+struct __is_ordered_integer_representable : false_type {};
+
+template <class _Tp>
+struct __is_ordered_integer_representable<_Tp, __void_t<decltype(__to_ordered_integral(std::declval<_Tp>()))>>
+    : true_type {};
+
+template <class _Tp>
+inline constexpr auto __is_ordered_integer_representable_v = __is_ordered_integer_representable<_Tp>::value;
+
 struct __low_byte_fn {
   template <class _Ip>
   _LIBCPP_HIDE_FROM_ABI constexpr uint8_t operator()(_Ip __integer) const {

libcxx/include/__algorithm/stable_sort.h

@@ -202,7 +202,7 @@ struct __stable_sort_switch {
 #if _LIBCPP_STD_VER >= 17
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI constexpr unsigned __radix_sort_min_bound() {
-  static_assert(is_integral_v<_Tp > || numeric_limits<_Tp>::is_iec559);
+  static_assert(__is_ordered_integer_representable_v<_Tp>);
   if constexpr (sizeof(_Tp) == 1) {
     return 1 << 8;
   }
@@ -212,7 +212,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr unsigned __radix_sort_min_bound() {
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI constexpr unsigned __radix_sort_max_bound() {
-  static_assert(is_integral_v<_Tp > || numeric_limits<_Tp>::is_iec559);
+  static_assert(__is_ordered_integer_representable_v<_Tp>);
   if constexpr (sizeof(_Tp) >= 8) {
     return 1 << 15;
   }
@@ -248,7 +248,7 @@ _LIBCPP_CONSTEXPR_SINCE_CXX26 void __stable_sort(
 #if _LIBCPP_STD_VER >= 17
   constexpr auto __default_comp = __desugars_to_v<__less_tag, _Compare, value_type, value_type >;
   constexpr auto __arithmetic_value =
-      (is_integral_v<value_type > || numeric_limits<value_type>::is_iec559) &&
+      __is_ordered_integer_representable_v<value_type> &&
       is_same_v< value_type&, __iter_reference<_RandomAccessIterator>>;
   if constexpr (__default_comp && __arithmetic_value) {
     if (__len <= __buff_size && __len >= static_cast<difference_type>(std::__radix_sort_min_bound<value_type>()) &&

libcxx/test/std/algorithms/alg.sorting/alg.sort/stable.sort/stable_sort.pass.cpp

@@ -250,6 +250,7 @@ int main(int, char**) {
   test<int>();
   test_floating<float>();
   test_floating<double>();
+  test_floating<long double>();
   test_enum();
 #if TEST_STD_VER >= 26
   static_assert(test<int>());