[libcxx-commits] [libcxx] [libcxx][algorithm] Optimize std::stable_sort via radix sort algorithm (PR #104683)

[Дмитрий Изволов via libcxx-commits]

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@@ -212,6 +240,22 @@ void __stable_sort(_RandomAccessIterator __first,
     std::__insertion_sort<_AlgPolicy, _Compare>(__first, __last, __comp);
     return;
   }
+
+#if _LIBCPP_STD_VER >= 17
+  constexpr auto __default_comp =
+      __desugars_to_v<__totally_ordered_less_tag, __remove_cvref_t<_Compare>, value_type, value_type >;
+  constexpr auto __integral_value =
+      is_integral_v<value_type > && is_same_v< value_type&, __iter_reference<_RandomAccessIterator>>;
+  constexpr auto __allowed_radix_sort = __default_comp && __integral_value;
+  if constexpr (__allowed_radix_sort) {
+    if (__len <= __buff_size && __len >= static_cast<difference_type>(__radix_sort_min_bound<value_type>()) &&
+        __len <= static_cast<difference_type>(__radix_sort_max_bound<value_type>())) {
+      std::__radix_sort(__first, __last, __buff);
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izvolov wrote:

I've extented test cases so we test both `int` and `float` arrays of sizes relevant to radix sort to ensure that both branches are covered.

https://github.com/llvm/llvm-project/pull/104683