Python like Range

docs/sphinx/user_guide/feature/iteration_spaces.rst

@@ -94,3 +94,68 @@ and two types:
 
 Thus, any iterable type that defines these methods and types appropriately
 can be used as a segment with RAJA kernel execution templates.
+
+Python-like Range Helpers
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+RAJA also provides ``RAJA::range(...)`` helpers that construct the segment
+type for common half-open iteration patterns. These helpers are intended to
+mirror the shape of Python's ``range`` while returning RAJA segment objects
+that can be passed directly to ``RAJA::forall`` and other execution
+interfaces.
+
+The supported forms are::
+
+  RAJA::range(end)                 // [0, end)
+  RAJA::range<IndexT>(end)         // [0, end) with explicit storage type
+  RAJA::range(begin, end)          // [begin, end)
+  RAJA::range(begin, end, stride)  // [begin, end) with stride
+
+The return type depends on the arguments:
+
+* ``RAJA::range(end)`` and ``RAJA::range(begin, end)`` return a
+  ``RAJA::TypedRangeSegment``.
+* ``RAJA::range(begin, end, stride)`` returns a
+  ``RAJA::TypedRangeStrideSegment``.
+* When one of the bounds is a RAJA strong index type, such as a type created
+  with ``RAJA_INDEX_VALUE``, that strong type is preserved for the loop
+  variable when possible.
+* Providing an explicit template argument, such as
+  ``RAJA::range<MyIndex>(end)``, overrides the deduced storage type.
+
+For example::
+
+  RAJA_INDEX_VALUE(CellIndex, "CellIndex");
+
+  RAJA::forall<RAJA::seq_exec>(RAJA::range(N), [=](RAJA::Index_type i) {
+    values[i] = i * i;
+  });
+
+  RAJA::forall<RAJA::seq_exec>(RAJA::range<CellIndex>(N), [=](CellIndex i) {
+    typed_values[*i] = *i + 10;
+  });
+
+  RAJA::forall<RAJA::seq_exec>(RAJA::range(2, 6), [=](int i) {
+    subrange_values[i] = i;
+  });
+
+  RAJA::forall<RAJA::seq_exec>(RAJA::range(CellIndex {1}, N, 2),
+                               [=](CellIndex i) {
+                                 strided_values[*i] = *i;
+                               });
+
+Strided ranges follow the same half-open interval convention as
+``RAJA::TypedRangeStrideSegment``. Positive strides move forward, and negative
+strides move backward. For example, ``RAJA::range(N - 1, -1, -2)`` visits
+``N - 1, N - 3, ...`` down to the first value that remains greater than
+``-1``. A zero stride is invalid and causes RAJA to abort or throw, depending
+on the build configuration.
+
+The older ``RAJA::make_range`` and ``RAJA::make_strided_range`` helpers remain
+available. Use ``RAJA::range(...)`` when the Python-like spelling improves
+readability or when you want the one-argument ``[0, end)`` shorthand.
+
+The complete example added in this branch is shown below:
+
+.. literalinclude:: ../../../../examples/raja-ranges.cpp
+   :language: c++

examples/CMakeLists.txt

@@ -19,6 +19,10 @@ raja_add_executable(
   NAME resource-forall
   SOURCES resource-forall.cpp)
 
+raja_add_executable(
+  NAME raja-ranges
+  SOURCES raja-ranges.cpp)
+
 raja_add_executable(
   NAME dynamic-forall
   SOURCES dynamic-forall.cpp)

examples/raja-ranges.cpp

@@ -0,0 +1,113 @@
+//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~//
+// Copyright (c) Lawrence Livermore National Security, LLC and other
+// RAJA Project Developers. See top-level LICENSE and COPYRIGHT
+// files for dates and other details. No copyright assignment is required
+// to contribute to RAJA.
+//
+// SPDX-License-Identifier: (BSD-3-Clause)
+//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~//
+
+#include <iostream>
+
+#include "RAJA/RAJA.hpp"
+
+/*
+ * RAJA ranges example
+ *
+ * Demonstrates Python-like range helpers backed by RAJA segments:
+ *   1. RAJA::range(N) for [0, N)
+ *   2. RAJA::range<T>(N) for a TypedRangeSegment<T> over [0, N)
+ *   3. RAJA::range(begin, end) for [begin, end)
+ *   4. RAJA::range(begin, end, step) for a strided half-open interval
+ *   5. Mixed strong/numeric begin/end and strided ranges
+ */
+
+RAJA_INDEX_VALUE(CellIndex, "CellIndex");
+
+int main(int RAJA_UNUSED_ARG(argc), char** RAJA_UNUSED_ARG(argv))
+{
+  constexpr RAJA::Index_type N = 8;
+
+  int values[N] = {};
+  int typed_values[N] = {};
+  int subrange_values[N] = {};
+  int odd_values[N] = {};
+  int mixed_end_values[N] = {};
+  int mixed_stride_values[N] = {};
+
+  // Equivalent to Python range(N): [0, N)
+  RAJA::forall<RAJA::seq_exec>(RAJA::range(N), [&](RAJA::Index_type i) {
+    values[i] = static_cast<int>(i * i);
+  });
+
+  // Equivalent to Python range(N), but preserving a strong index type.
+  RAJA::forall<RAJA::seq_exec>(RAJA::range<CellIndex>(N), [&](CellIndex i) {
+    typed_values[*i] = static_cast<int>(*i + 10);
+  });
+
+  // Equivalent to Python range(2, 6): [2, 6)
+  RAJA::forall<RAJA::seq_exec>(RAJA::range(2, 6), [&](int i) {
+    subrange_values[i] = i;
+  });
+
+  // Equivalent to Python range(1, N, 2): odd indices in [1, N)
+  RAJA::forall<RAJA::seq_exec>(RAJA::range(1, N, 2), [&](int i) {
+    odd_values[i] = i;
+  });
+
+  // Mixed numeric/strong range: preserves CellIndex for the loop index.
+  RAJA::forall<RAJA::seq_exec>(RAJA::range(1, CellIndex {6}), [&](CellIndex i) {
+    mixed_end_values[*i] = static_cast<int>(*i * 10);
+  });
+
+  // Mixed strong begin with numeric end/stride for a strided range.
+  RAJA::forall<RAJA::seq_exec>(RAJA::range(CellIndex {1}, N, 2),
+                               [&](CellIndex i) {
+                                 mixed_stride_values[*i] =
+                                     static_cast<int>(*i * 100);
+                               });
+
+  std::cout << "range(N):";
+  for (auto i : RAJA::range(N)) {
+    std::cout << ' ' << values[i];
+  }
+  std::cout << '\n';
+
+  std::cout << "range<CellIndex>(N):";
+  for (auto i : RAJA::range<CellIndex>(N)) {
+    std::cout << ' ' << typed_values[*i];
+  }
+  std::cout << '\n';
+
+  std::cout << "range(2, 6):";
+  for (auto i : RAJA::range(2, 6)) {
+    std::cout << ' ' << subrange_values[i];
+  }
+  std::cout << '\n';
+
+  std::cout << "range(1, N, 2):";
+  for (auto i : RAJA::range(1, N, 2)) {
+    std::cout << ' ' << odd_values[i];
+  }
+  std::cout << '\n';
+
+  std::cout << "range(1, CellIndex{6}):";
+  for (auto i : RAJA::range(1, CellIndex {6})) {
+    std::cout << ' ' << mixed_end_values[*i];
+  }
+  std::cout << '\n';
+
+  std::cout << "range(CellIndex{1}, N, 2):";
+  for (auto i : RAJA::range(CellIndex {1}, N, 2)) {
+    std::cout << ' ' << mixed_stride_values[*i];
+  }
+  std::cout << '\n';
+
+  std::cout << "range(N - 1, -1, -2):";
+  for (auto i : RAJA::range(N - 1, -1, -2)) {
+    std::cout << ' ' << i;
+  }
+  std::cout << '\n';
+
+  return 0;
+}