Port aligned_accessor from the Raft fork of Kokkos to mainline.

include/experimental/__p0009_bits/aligned_accessor.hpp

@@ -0,0 +1,177 @@
+/*
+//@HEADER
+// ************************************************************************
+//
+//                        Kokkos v. 2.0
+//              Copyright (2019) Sandia Corporation
+//
+// Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation,
+// the U.S. Government retains certain rights in this software.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// 1. Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright
+// notice, this list of conditions and the following disclaimer in the
+// documentation and/or other materials provided with the distribution.
+//
+// 3. Neither the name of the Corporation nor the names of the
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY SANDIA CORPORATION "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SANDIA CORPORATION OR THE
+// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// Questions? Contact Christian R. Trott ([email protected])
+//
+// ************************************************************************
+//@HEADER
+*/
+
+
+// NOTE: This code is prematurely taken from an example based on
+// https://github.com/kokkos/mdspan/pull/176
+
+#pragma once
+
+#include "macros.hpp"
+#include "trait_backports.hpp"
+#include "default_accessor.hpp"
+#include "extents.hpp"
+#include <bit>
+#include <cassert>
+#include <iostream>
+#include <memory>
+#include <type_traits>
+
+namespace MDSPAN_IMPL_STANDARD_NAMESPACE {
+namespace MDSPAN_IMPL_PROPOSED_NAMESPACE {
+
+// Prefer std::assume_aligned if available, as it is in the C++ Standard.
+// Otherwise, use a compiler-specific equivalent if available.
+
+// NOTE (mfh 2022/08/08) BYTE_ALIGNMENT must be unsigned and a power of 2.
+#if defined(__cpp_lib_assume_aligned)
+#  define MDSPAN_IMPL_ASSUME_ALIGNED( ELEMENT_TYPE, POINTER, BYTE_ALIGNMENT ) (std::assume_aligned< BYTE_ALIGNMENT >( POINTER ))
+  constexpr char assume_aligned_method[] = "std::assume_aligned";
+#elif defined(__ICL)
+#  define _MDSPAN_ASSUME_ALIGNED( ELEMENT_TYPE, POINTER, BYTE_ALIGNMENT ) POINTER
+  constexpr char assume_aligned_method[] = "(none)";
+#elif defined(__ICC)
+#  define _MDSPAN_ASSUME_ALIGNED( ELEMENT_TYPE, POINTER, BYTE_ALIGNMENT ) POINTER
+  constexpr char assume_aligned_method[] = "(none)";
+#elif defined(__clang__)
+#  define _MDSPAN_ASSUME_ALIGNED( ELEMENT_TYPE, POINTER, BYTE_ALIGNMENT ) POINTER
+  constexpr char assume_aligned_method[] = "(none)";
+#elif defined(__GNUC__)
+  // __builtin_assume_aligned returns void*
+#  define _MDSPAN_ASSUME_ALIGNED( ELEMENT_TYPE, POINTER, BYTE_ALIGNMENT ) reinterpret_cast< ELEMENT_TYPE* >(__builtin_assume_aligned( POINTER, BYTE_ALIGNMENT ))
+  constexpr char assume_aligned_method[] = "__builtin_assume_aligned";
+#else
+#  define _MDSPAN_ASSUME_ALIGNED( ELEMENT_TYPE, POINTER, BYTE_ALIGNMENT ) POINTER
+  constexpr char assume_aligned_method[] = "(none)";
+#endif
+
+// Some compilers other than Clang or GCC like to define __clang__ or __GNUC__.
+// Thus, we order the tests from most to least specific.
+#if defined(__ICL)
+#  define _MDSPAN_ALIGN_VALUE_ATTRIBUTE( BYTE_ALIGNMENT ) __declspec(align_value( BYTE_ALIGNMENT ));
+  constexpr char align_attribute_method[] = "__declspec(align_value(BYTE_ALIGNMENT))";
+#elif defined(__ICC)
+#  define _MDSPAN_ALIGN_VALUE_ATTRIBUTE( BYTE_ALIGNMENT ) __attribute__((align_value( BYTE_ALIGNMENT )));
+  constexpr char align_attribute_method[] = "__attribute__((align_value(BYTE_ALIGNMENT)))";
+#elif defined(__clang__)
+#  define _MDSPAN_ALIGN_VALUE_ATTRIBUTE( BYTE_ALIGNMENT ) __attribute__((align_value( BYTE_ALIGNMENT )));
+  constexpr char align_attribute_method[] = "__attribute__((align_value(BYTE_ALIGNMENT)))";
+#else
+#  define _MDSPAN_ALIGN_VALUE_ATTRIBUTE( BYTE_ALIGNMENT )
+  constexpr char align_attribute_method[] = "(none)";
+#endif
+
+constexpr bool
+is_nonzero_power_of_two(const std::size_t x)
+{
+// Just checking __cpp_lib_int_pow2 isn't enough for some GCC versions.
+// The <bit> header exists, but std::has_single_bit does not.
+#if defined(__cpp_lib_int_pow2) && __cplusplus >= 202002L
+  return std::has_single_bit(x);
+#else
+  return x != 0 && (x & (x - 1)) == 0;
+#endif
+}
+
+template<class ElementType>
+constexpr bool
+valid_byte_alignment(const std::size_t byte_alignment)
+{
+  return is_nonzero_power_of_two(byte_alignment) && byte_alignment >= alignof(ElementType);
+}
+
+// We define aligned_pointer_t through a struct
+// so we can check whether the byte alignment is valid.
+// This makes it impossible to use the alias
+// with an invalid byte alignment.
+template<class ElementType, std::size_t byte_alignment>
+struct aligned_pointer {
+  static_assert(valid_byte_alignment<ElementType>(byte_alignment),
+		"byte_alignment must be a power of two no less than "
+		"the minimum required alignment of ElementType.");
+  using type = ElementType* _MDSPAN_ALIGN_VALUE_ATTRIBUTE( byte_alignment );
+};
+
+
+template<class ElementType, std::size_t byte_alignment>
+using aligned_pointer_t = typename aligned_pointer<ElementType, byte_alignment>::type;
+
+template<class ElementType, std::size_t byte_alignment>
+aligned_pointer_t<ElementType, byte_alignment>
+bless(ElementType* ptr, std::integral_constant<std::size_t, byte_alignment> /* ba */ )
+{
+  return _MDSPAN_ASSUME_ALIGNED( ElementType, ptr, byte_alignment );
+}
+
+
+template<class ElementType, std::size_t byte_alignment>
+struct aligned_accessor {
+  using offset_policy = MDSPAN_IMPL_STANDARD_NAMESPACE::default_accessor<ElementType>;
+  using element_type = ElementType;
+  using reference = ElementType&;
+  using data_handle_type = aligned_pointer_t<ElementType, byte_alignment>;
+
+  constexpr aligned_accessor() noexcept = default;
+
+  MDSPAN_TEMPLATE_REQUIRES(
+    class OtherElementType,
+    std::size_t OtherByteAlignment,
+    /* requires */ (std::is_convertible<OtherElementType(*)[], element_type(*)[]>::value && OtherByteAlignment >= byte_alignment)
+    )
+  constexpr aligned_accessor(aligned_accessor<OtherElementType, other_byte_alignment>) noexcept {}
+
+  constexpr reference access(data_handle_type p, size_t i) const noexcept {
+    // This may declare alignment twice, depending on
+    // if we have an attribute for marking pointer types.
+    return _MDSPAN_ASSUME_ALIGNED( ElementType, p, byte_alignment )[i];
+  }
+
+  constexpr typename offset_policy::data_handle_type
+  offset(data_handle_type p, size_t i) const noexcept {
+    return p + i;
+  }
+};
+
+
+}  // namespace MDSPAN_IMPL_PROPOSED_NAMESPACE
+}  // namespace MDSPAN_IMPL_STANDARD_NAMESPACE