From 294fbfbf97c6cd9175b33d9a685f4228c996d04e Mon Sep 17 00:00:00 2001
From: sleepingeight <theallrounder.mst@gmail.com>
Date: Thu, 26 Feb 2026 23:20:05 +0530
Subject: [PATCH] 1/n: conforming parallel range algos to the standard

Signed-off-by: sleepingeight <theallrounder.mst@gmail.com>
---
 .../adjacent_difference.hpp                   | 141 ++++--------------
 .../adjacentdifference_range.cpp              |   4 +-
 .../adjacentdifference_range_sender.cpp       |   2 +-
 .../unit/container_algorithms/test_utils.hpp  |  13 +-
 4 files changed, 45 insertions(+), 115 deletions(-)

diff --git a/libs/core/algorithms/include/hpx/parallel/container_algorithms/adjacent_difference.hpp b/libs/core/algorithms/include/hpx/parallel/container_algorithms/adjacent_difference.hpp
index 37c8a9b1a4be..6cf32ed2120f 100644
--- a/libs/core/algorithms/include/hpx/parallel/container_algorithms/adjacent_difference.hpp
+++ b/libs/core/algorithms/include/hpx/parallel/container_algorithms/adjacent_difference.hpp
@@ -353,172 +353,91 @@ namespace hpx::ranges {
       : hpx::detail::tag_parallel_algorithm<adjacent_difference_t>
     {
     private:
-        template <typename FwdIter1, typename FwdIter2, typename Sent>
-        // clang-format off
-             requires (
-                hpx::traits::is_iterator_v<FwdIter1> &&
-                hpx::traits::is_iterator_v<FwdIter2> &&
-                std::sentinel_for<Sent, FwdIter1>
-            )
-        // clang-format on
+        template <std::forward_iterator FwdIter1,
+            std::forward_iterator FwdIter2, std::sentinel_for<FwdIter1> Sent>
         friend FwdIter2 tag_fallback_invoke(hpx::ranges::adjacent_difference_t,
             FwdIter1 first, Sent last, FwdIter2 dest)
         {
-            static_assert(std::forward_iterator<FwdIter1>,
-                "Required at least forward iterator.");
-            static_assert(std::forward_iterator<FwdIter2>,
-                "Required at least forward iterator.");
-
             return hpx::parallel::detail::adjacent_difference<FwdIter2>().call(
                 hpx::execution::seq, first, last, dest, std::minus<>());
         }
 
-        template <typename Rng, typename FwdIter2>
-        // clang-format off
-            requires(std::ranges::range<Rng> &&
-                hpx::traits::is_iterator_v<FwdIter2>)
-        // clang-format on
+        template <std::ranges::forward_range Rng,
+            std::forward_iterator FwdIter2>
         friend FwdIter2 tag_fallback_invoke(
             hpx::ranges::adjacent_difference_t, Rng&& rng, FwdIter2 dest)
         {
-            static_assert(std::forward_iterator<std::ranges::iterator_t<Rng>>,
-                "Required at least forward iterator.");
-            static_assert(std::forward_iterator<FwdIter2>,
-                "Required at least forward iterator.");
-
             return hpx::parallel::detail::adjacent_difference<FwdIter2>().call(
                 hpx::execution::seq, hpx::util::begin(rng), hpx::util::end(rng),
                 dest, std::minus<>());
         }
 
-        template <typename ExPolicy, typename FwdIter1, typename Sent,
-            typename FwdIter2>
-        // clang-format off
-            requires (
-                hpx::is_execution_policy_v<ExPolicy> &&
-                hpx::traits::is_iterator_v<FwdIter1> &&
-                hpx::traits::is_iterator_v<FwdIter2> &&
-                std::sentinel_for<Sent, FwdIter1>
-            )
-        // clang-format on
+        template <hpx::execution_policy ExPolicy,
+            std::random_access_iterator RaIter1,
+            std::sized_sentinel_for<RaIter1> Sent,
+            std::random_access_iterator RaIter2>
         friend decltype(auto) tag_fallback_invoke(
             hpx::ranges::adjacent_difference_t, ExPolicy&& policy,
-            FwdIter1 first, Sent last, FwdIter2 dest)
+            RaIter1 first, Sent last, RaIter2 dest)
         {
-            static_assert(std::forward_iterator<FwdIter1>,
-                "Required at least forward iterator.");
-            static_assert(std::forward_iterator<FwdIter2>,
-                "Required at least forward iterator.");
-
-            return hpx::parallel::detail::adjacent_difference<FwdIter2>().call(
+            return hpx::parallel::detail::adjacent_difference<RaIter2>().call(
                 HPX_FORWARD(ExPolicy, policy), first, last, dest,
                 std::minus<>());
         }
 
-        template <typename ExPolicy, typename Rng, typename FwdIter2>
-        // clang-format off
-            requires (
-                hpx::is_execution_policy_v<ExPolicy> &&
-                std::ranges::range<Rng> &&
-                hpx::traits::is_iterator_v<FwdIter2>
-            )
-        // clang-format on
+        template <hpx::execution_policy ExPolicy,
+            std::ranges::random_access_range Rng,
+            std::random_access_iterator RaIter2>
         friend decltype(auto) tag_fallback_invoke(
             hpx::ranges::adjacent_difference_t, ExPolicy&& policy, Rng&& rng,
-            FwdIter2 dest)
+            RaIter2 dest)
         {
-            static_assert(std::forward_iterator<std::ranges::iterator_t<Rng>>,
-                "Required at least forward iterator.");
-            static_assert(std::forward_iterator<FwdIter2>,
-                "Required at least forward iterator.");
-
-            return hpx::parallel::detail::adjacent_difference<FwdIter2>().call(
+            return hpx::parallel::detail::adjacent_difference<RaIter2>().call(
                 HPX_FORWARD(ExPolicy, policy), hpx::util::begin(rng),
                 hpx::util::end(rng), dest, std::minus<>());
         }
 
-        template <typename FwdIter1, typename Sent, typename FwdIter2,
+        template <std::forward_iterator FwdIter1,
+            std::sentinel_for<FwdIter1> Sent, std::forward_iterator FwdIter2,
             typename Op>
-        // clang-format off
-            requires(hpx::traits::is_iterator_v<FwdIter1> &&
-                hpx::traits::is_iterator_v<FwdIter2> &&
-                std::sentinel_for<Sent, FwdIter1>)
-        // clang-format on
         friend FwdIter2 tag_fallback_invoke(hpx::ranges::adjacent_difference_t,
             FwdIter1 first, Sent last, FwdIter2 dest, Op op)
         {
-            static_assert(std::forward_iterator<FwdIter1>,
-                "Required at least forward iterator.");
-            static_assert(std::forward_iterator<FwdIter2>,
-                "Required at least forward iterator.");
-
             return hpx::parallel::detail::adjacent_difference<FwdIter2>().call(
                 hpx::execution::sequenced_policy{}, first, last, dest,
                 HPX_MOVE(op));
         }
 
-        template <typename Rng, typename FwdIter2, typename Op>
-        // clang-format off
-             requires (
-                std::ranges::range<Rng> &&
-                hpx::traits::is_iterator_v<FwdIter2>
-            )
-        // clang-format on
+        template <std::ranges::forward_range Rng,
+            std::forward_iterator FwdIter2, typename Op>
         friend FwdIter2 tag_fallback_invoke(
             hpx::ranges::adjacent_difference_t, Rng&& rng, FwdIter2 dest, Op op)
         {
-            static_assert(std::forward_iterator<std::ranges::iterator_t<Rng>>,
-                "Required at least forward iterator.");
-            static_assert(std::forward_iterator<FwdIter2>,
-                "Required at least forward iterator.");
-
             return hpx::parallel::detail::adjacent_difference<FwdIter2>().call(
                 hpx::execution::seq, hpx::util::begin(rng), hpx::util::end(rng),
                 dest, HPX_MOVE(op));
         }
 
-        template <typename ExPolicy, typename FwdIter1, typename Sent,
-            typename FwdIter2, typename Op>
-        // clang-format off
-            requires (
-                hpx::is_execution_policy_v<ExPolicy> &&
-                hpx::traits::is_iterator_v<FwdIter1> &&
-                hpx::traits::is_iterator_v<FwdIter2> &&
-                std::sentinel_for<Sent, FwdIter1>
-            )
-        // clang-format on
+        template <hpx::execution_policy ExPolicy,
+            std::random_access_iterator RaIter1,
+            std::sized_sentinel_for<RaIter1> Sent,
+            std::random_access_iterator RaIter2, typename Op>
         friend decltype(auto) tag_fallback_invoke(
             hpx::ranges::adjacent_difference_t, ExPolicy&& policy,
-            FwdIter1 first, Sent last, FwdIter2 dest, Op op)
+            RaIter1 first, Sent last, RaIter2 dest, Op op)
         {
-            static_assert(std::forward_iterator<FwdIter1>,
-                "Required at least forward iterator.");
-            static_assert(std::forward_iterator<FwdIter2>,
-                "Required at least forward iterator.");
-
-            return hpx::parallel::detail::adjacent_difference<FwdIter2>().call(
+            return hpx::parallel::detail::adjacent_difference<RaIter2>().call(
                 HPX_FORWARD(ExPolicy, policy), first, last, dest, HPX_MOVE(op));
         }
 
-        template <typename ExPolicy, typename Rng, typename FwdIter2,
-            typename Op>
-        // clang-format off
-            requires (
-                hpx::is_execution_policy_v<ExPolicy> &&
-                std::ranges::range<Rng> &&
-                hpx::traits::is_iterator_v<FwdIter2>
-            )
-        // clang-format on
+        template <hpx::execution_policy ExPolicy,
+            std::ranges::random_access_range Rng,
+            std::random_access_iterator RaIter2, typename Op>
         friend decltype(auto) tag_fallback_invoke(
             hpx::ranges::adjacent_difference_t, ExPolicy&& policy, Rng&& rng,
-            FwdIter2 dest, Op op)
+            RaIter2 dest, Op op)
         {
-            static_assert(std::forward_iterator<std::ranges::iterator_t<Rng>>,
-                "Required at least forward iterator.");
-            static_assert(std::forward_iterator<FwdIter2>,
-                "Required at least forward iterator.");
-
-            return hpx::parallel::detail::adjacent_difference<FwdIter2>().call(
+            return hpx::parallel::detail::adjacent_difference<RaIter2>().call(
                 HPX_FORWARD(ExPolicy, policy), hpx::util::begin(rng),
                 hpx::util::end(rng), dest, HPX_MOVE(op));
         }
diff --git a/libs/core/algorithms/tests/unit/container_algorithms/adjacentdifference_range.cpp b/libs/core/algorithms/tests/unit/container_algorithms/adjacentdifference_range.cpp
index 0d52f56ca4e1..6b95c8eed39e 100644
--- a/libs/core/algorithms/tests/unit/container_algorithms/adjacentdifference_range.cpp
+++ b/libs/core/algorithms/tests/unit/container_algorithms/adjacentdifference_range.cpp
@@ -31,8 +31,8 @@ void test_sen(ExPolicy policy)
     std::vector<std::size_t> d(10007);
     std::vector<std::size_t> d_ans(10007);
 
-    auto it = hpx::ranges::adjacent_difference(
-        policy, std::begin(c), sentinel<std::size_t>{10007}, std::begin(d));
+    auto it = hpx::ranges::adjacent_difference(policy, std::begin(c),
+        test::sentinel_from_iterator(std::end(c) - 1), std::begin(d));
     std::adjacent_difference(std::begin(c), std::end(c), std::begin(d_ans));
 
     HPX_TEST(std::equal(std::begin(d), std::end(d) - 1, std::begin(d_ans),
diff --git a/libs/core/algorithms/tests/unit/container_algorithms/adjacentdifference_range_sender.cpp b/libs/core/algorithms/tests/unit/container_algorithms/adjacentdifference_range_sender.cpp
index 0f9f127aded6..6e7275f098ea 100644
--- a/libs/core/algorithms/tests/unit/container_algorithms/adjacentdifference_range_sender.cpp
+++ b/libs/core/algorithms/tests/unit/container_algorithms/adjacentdifference_range_sender.cpp
@@ -39,7 +39,7 @@ void test_sen_direct(Policy l, ExPolicy&& policy)
 
     auto exec = ex::explicit_scheduler_executor(scheduler_t(l));
     auto it = hpx::ranges::adjacent_difference(policy.on(exec), std::begin(c),
-        sentinel<std::size_t>{10007}, std::begin(d));
+        test::sentinel_from_iterator(std::end(c) - 1), std::begin(d));
 
     std::adjacent_difference(std::begin(c), std::end(c), std::begin(d_ans));
 
diff --git a/libs/core/algorithms/tests/unit/container_algorithms/test_utils.hpp b/libs/core/algorithms/tests/unit/container_algorithms/test_utils.hpp
index 1416bf683a10..e08a61fb090e 100644
--- a/libs/core/algorithms/tests/unit/container_algorithms/test_utils.hpp
+++ b/libs/core/algorithms/tests/unit/container_algorithms/test_utils.hpp
@@ -18,7 +18,6 @@
 #include <iterator>
 #include <numeric>
 #include <random>
-#include <sys/stat.h>
 #include <type_traits>
 #include <utility>
 #include <vector>
@@ -63,6 +62,18 @@ namespace test {
             return i != s.get();
         }
 
+        friend auto operator-(sentinel_from_iterator<IterType> s, IterType i)
+            requires std::random_access_iterator<IterType>
+        {
+            return s.get() - i;
+        }
+
+        friend auto operator-(IterType i, sentinel_from_iterator<IterType> s)
+            requires std::random_access_iterator<IterType>
+        {
+            return i - s.get();
+        }
+
     private:
         IterType end;
     };