Allow using counting_iterator with datapar policies

Signed-off-by: Hartmut Kaiser <hartmut.kaiser@gmail.com>

Author: hkaiser

.github/workflows/linux_crosscompile_arm_eve_sve_release.yml

@@ -50,6 +50,7 @@ jobs:
           cmake --build build --target core
           cmake --build build --target tests.unit.modules.algorithms.datapar_algorithms
           cmake --build build --target tests.regressions.modules.algorithms.for_each_datapar
+          cmake --build build --target tests.regressions.modules.algorithms.counting_iterator_datapar
     - name: Test
       shell: bash
       run: |

.github/workflows/linux_crosscompile_arm_sve_release.yml

@@ -50,6 +50,7 @@ jobs:
           cmake --build build --target core
           cmake --build build --target tests.unit.modules.algorithms.datapar_algorithms
           cmake --build build --target tests.regressions.modules.algorithms.for_each_datapar
+          cmake --build build --target tests.regressions.modules.algorithms.counting_iterator_datapar
     - name: Test
       shell: bash
       run: |

libs/core/algorithms/include/hpx/parallel/algorithms/count.hpp

@@ -272,9 +272,9 @@ namespace hpx::parallel {
             count_iteration& operator=(count_iteration&&) = default;
 
             template <typename Iter>
-            HPX_HOST_DEVICE HPX_FORCEINLINE constexpr
-                typename std::iterator_traits<Iter>::difference_type
-                operator()(Iter part_begin, std::size_t part_size)
+            HPX_HOST_DEVICE HPX_FORCEINLINE constexpr std::iterator_traits<
+                Iter>::difference_type
+            operator()(Iter part_begin, std::size_t part_size)
             {
                 typename std::iterator_traits<Iter>::difference_type ret = 0;
                 util::loop_n<execution_policy_type>(part_begin, part_size,
@@ -283,8 +283,8 @@ namespace hpx::parallel {
             }
 
             template <typename Iter>
-            HPX_HOST_DEVICE HPX_FORCEINLINE constexpr void operator()(Iter curr,
-                typename std::iterator_traits<Iter>::difference_type& ret)
+            HPX_HOST_DEVICE HPX_FORCEINLINE constexpr void operator()(
+                Iter curr, std::iterator_traits<Iter>::difference_type& ret)
             {
                 ret += traits::count_bits(
                     HPX_INVOKE(op_, HPX_INVOKE(proj_, *curr)));
@@ -295,7 +295,7 @@ namespace hpx::parallel {
         HPX_CXX_CORE_EXPORT template <typename Value>
         struct count : public algorithm<count<Value>, Value>
         {
-            typedef Value difference_type;
+            using difference_type = Value;
 
             constexpr count() noexcept
               : algorithm<count, Value>("count")
@@ -430,20 +430,16 @@ namespace hpx {
     private:
         template <typename ExPolicy, typename FwdIter,
             typename T = typename std::iterator_traits<FwdIter>::value_type>
-        // clang-format off
-            requires (
-                hpx::is_execution_policy_v<ExPolicy> &&
-                hpx::traits::is_iterator_v<FwdIter>
-            )
-        // clang-format on
+            requires(hpx::is_execution_policy_v<ExPolicy> &&
+                hpx::traits::is_iterator_v<FwdIter>)
         friend decltype(auto) tag_fallback_invoke(count_t, ExPolicy&& policy,
             FwdIter first, FwdIter last, T const& value)
         {
             static_assert(std::forward_iterator<FwdIter>,
                 "Required at least forward iterator.");
 
             using difference_type =
-                typename std::iterator_traits<FwdIter>::difference_type;
+                std::iterator_traits<FwdIter>::difference_type;
 
             return hpx::parallel::detail::count<difference_type>().call(
                 HPX_FORWARD(ExPolicy, policy), first, last, value,
@@ -452,19 +448,15 @@ namespace hpx {
 
         template <typename InIter,
             typename T = typename std::iterator_traits<InIter>::value_type>
-        // clang-format off
-            requires (
-                hpx::traits::is_iterator_v<InIter>
-            )
-        // clang-format on
-        friend typename std::iterator_traits<InIter>::difference_type
-        tag_fallback_invoke(count_t, InIter first, InIter last, T const& value)
+            requires(hpx::traits::is_iterator_v<InIter>)
+        friend decltype(auto) tag_fallback_invoke(
+            count_t, InIter first, InIter last, T const& value)
         {
             static_assert(std::input_iterator<InIter>,
                 "Required at least input iterator.");
 
             using difference_type =
-                typename std::iterator_traits<InIter>::difference_type;
+                std::iterator_traits<InIter>::difference_type;
 
             return hpx::parallel::detail::count<difference_type>().call(
                 hpx::execution::seq, first, last, value, hpx::identity_v);
@@ -494,30 +486,25 @@ namespace hpx {
                 "Required at least forward iterator.");
 
             using difference_type =
-                typename std::iterator_traits<FwdIter>::difference_type;
+                std::iterator_traits<FwdIter>::difference_type;
 
             return hpx::parallel::detail::count_if<difference_type>().call(
                 HPX_FORWARD(ExPolicy, policy), first, last, HPX_MOVE(f),
                 hpx::identity_v);
         }
 
         template <typename InIter, typename F>
-        // clang-format off
-            requires (
-                hpx::traits::is_iterator_v<InIter> &&
+            requires(hpx::traits::is_iterator_v<InIter> &&
                 hpx::is_invocable_v<F,
-                    typename std::iterator_traits<InIter>::value_type
-                >
-            )
-        // clang-format on
-        friend typename std::iterator_traits<InIter>::difference_type
-        tag_fallback_invoke(count_if_t, InIter first, InIter last, F f)
+                    typename std::iterator_traits<InIter>::value_type>)
+        friend decltype(auto) tag_fallback_invoke(
+            count_if_t, InIter first, InIter last, F f)
         {
             static_assert(std::input_iterator<InIter>,
                 "Required at least input iterator.");
 
             using difference_type =
-                typename std::iterator_traits<InIter>::difference_type;
+                std::iterator_traits<InIter>::difference_type;
 
             return hpx::parallel::detail::count_if<difference_type>().call(
                 hpx::execution::seq, first, last, HPX_MOVE(f), hpx::identity_v);