// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// Kokkos v. 4.0
// Copyright (2022) National Technology & Engineering
// Solutions of Sandia, LLC (NTESS).
//
// Under the terms of Contract DE-NA0003525 with NTESS,
// the U.S. Government retains certain rights in this software.
//
//===---------------------------------------------------------------------===//
#ifndef _LIBCPP___MDSPAN_LAYOUT_STRIDE_H
#define _LIBCPP___MDSPAN_LAYOUT_STRIDE_H
#include <__assert>
#include <__concepts/same_as.h>
#include <__config>
#include <__fwd/mdspan.h>
#include <__mdspan/extents.h>
#include <__type_traits/common_type.h>
#include <__type_traits/is_constructible.h>
#include <__type_traits/is_convertible.h>
#include <__type_traits/is_integral.h>
#include <__type_traits/is_nothrow_constructible.h>
#include <__type_traits/is_same.h>
#include <__utility/as_const.h>
#include <__utility/integer_sequence.h>
#include <__utility/swap.h>
#include <array>
#include <cinttypes>
#include <cstddef>
#include <limits>
#include <span>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
_LIBCPP_PUSH_MACROS
#include <__undef_macros>
_LIBCPP_BEGIN_NAMESPACE_STD
#if _LIBCPP_STD_VER >= 23
namespace __mdspan_detail {
template <class _Layout, class _Mapping>
constexpr bool __is_mapping_of =
is_same_v<typename _Layout::template mapping<typename _Mapping::extents_type>, _Mapping>;
template <class _Mapping>
concept __layout_mapping_alike = requires {
requires __is_mapping_of<typename _Mapping::layout_type, _Mapping>;
requires __is_extents_v<typename _Mapping::extents_type>;
{ _Mapping::is_always_strided() } -> same_as<bool>;
{ _Mapping::is_always_exhaustive() } -> same_as<bool>;
{ _Mapping::is_always_unique() } -> same_as<bool>;
bool_constant<_Mapping::is_always_strided()>::value;
bool_constant<_Mapping::is_always_exhaustive()>::value;
bool_constant<_Mapping::is_always_unique()>::value;
};
} // namespace __mdspan_detail
template <class _Extents>
class layout_stride::mapping {
public:
static_assert(__mdspan_detail::__is_extents<_Extents>::value,
"layout_stride::mapping template argument must be a specialization of extents.");
using extents_type = _Extents;
using index_type = typename extents_type::index_type;
using size_type = typename extents_type::size_type;
using rank_type = typename extents_type::rank_type;
using layout_type = layout_stride;
private:
static constexpr rank_type __rank_ = extents_type::rank();
// Used for default construction check and mandates
_LIBCPP_HIDE_FROM_ABI static constexpr bool __required_span_size_is_representable(const extents_type& __ext) {
if constexpr (__rank_ == 0)
return true;
index_type __prod = __ext.extent(0);
for (rank_type __r = 1; __r < __rank_; __r++) {
bool __overflowed = __builtin_mul_overflow(__prod, __ext.extent(__r), &__prod);
if (__overflowed)
return false;
}
return true;
}
template <class _OtherIndexType>
_LIBCPP_HIDE_FROM_ABI static constexpr bool
__required_span_size_is_representable(const extents_type& __ext, span<_OtherIndexType, __rank_> __strides) {
if constexpr (__rank_ == 0)
return true;
index_type __size = 1;
for (rank_type __r = 0; __r < __rank_; __r++) {
// We can only check correct conversion of _OtherIndexType if it is an integral
if constexpr (is_integral_v<_OtherIndexType>) {
using _CommonType = common_type_t<index_type, _OtherIndexType>;
if (static_cast<_CommonType>(__strides[__r]) > static_cast<_CommonType>(numeric_limits<index_type>::max()))
return false;
}
if (__ext.extent(__r) == static_cast<index_type>(0))
return true;
index_type __prod = (__ext.extent(__r) - 1);
bool __overflowed_mul = __builtin_mul_overflow(__prod, static_cast<index_type>(__strides[__r]), &__prod);
if (__overflowed_mul)
return false;
bool __overflowed_add = __builtin_add_overflow(__size, __prod, &__size);
if (__overflowed_add)
return false;
}
return true;
}
// compute offset of a strided layout mapping
template <class _StridedMapping>
_LIBCPP_HIDE_FROM_ABI static constexpr index_type __offset(const _StridedMapping& __mapping) {
if constexpr (_StridedMapping::extents_type::rank() == 0) {
return static_cast<index_type>(__mapping());
} else if (__mapping.required_span_size() == static_cast<typename _StridedMapping::index_type>(0)) {
return static_cast<index_type>(0);
} else {
return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
return static_cast<index_type>(__mapping((_Pos ? 0 : 0)...));
}(make_index_sequence<__rank_>());
}
}
// compute the permutation for sorting the stride array
// we never actually sort the stride array
_LIBCPP_HIDE_FROM_ABI constexpr void __bubble_sort_by_strides(array<rank_type, __rank_>& __permute) const {
for (rank_type __i = __rank_ - 1; __i > 0; __i--) {
for (rank_type __r = 0; __r < __i; __r++) {
if (__strides_[__permute[__r]] > __strides_[__permute[__r + 1]]) {
swap(__permute[__r], __permute[__r + 1]);
} else {
// if two strides are the same then one of the associated extents must be 1 or 0
// both could be, but you can't have one larger than 1 come first
if ((__strides_[__permute[__r]] == __strides_[__permute[__r + 1]]) &&
(__extents_.extent(__permute[__r]) > static_cast<index_type>(1)))
swap(__permute[__r], __permute[__r + 1]);
}
}
}
}
static_assert(extents_type::rank_dynamic() > 0 || __required_span_size_is_representable(extents_type()),
"layout_stride::mapping product of static extents must be representable as index_type.");
public:
// [mdspan.layout.stride.cons], constructors
_LIBCPP_HIDE_FROM_ABI constexpr mapping() noexcept : __extents_(extents_type()) {
// Note the nominal precondition is covered by above static assert since
// if rank_dynamic is != 0 required_span_size is zero for default construction
if constexpr (__rank_ > 0) {
index_type __stride = 1;
for (rank_type __r = __rank_ - 1; __r > static_cast<rank_type>(0); __r--) {
__strides_[__r] = __stride;
__stride *= __extents_.extent(__r);
}
__strides_[0] = __stride;
}
}
_LIBCPP_HIDE_FROM_ABI constexpr mapping(const mapping&) noexcept = default;
template <class _OtherIndexType>
requires(is_convertible_v<const _OtherIndexType&, index_type> &&
is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
_LIBCPP_HIDE_FROM_ABI constexpr mapping(const extents_type& __ext, span<_OtherIndexType, __rank_> __strides) noexcept
: __extents_(__ext), __strides_([&]<size_t... _Pos>(index_sequence<_Pos...>) {
return __mdspan_detail::__possibly_empty_array<index_type, __rank_>{
static_cast<index_type>(std::as_const(__strides[_Pos]))...};
}(make_index_sequence<__rank_>())) {
_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
([&]<size_t... _Pos>(index_sequence<_Pos...>) {
// For integrals we can do a pre-conversion check, for other types not
if constexpr (is_integral_v<_OtherIndexType>) {
return ((__strides[_Pos] > static_cast<_OtherIndexType>(0)) && ... && true);
} else {
return ((static_cast<index_type>(__strides[_Pos]) > static_cast<index_type>(0)) && ... && true);
}
}(make_index_sequence<__rank_>())),
"layout_stride::mapping ctor: all strides must be greater than 0");
_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
__required_span_size_is_representable(__ext, __strides),
"layout_stride::mapping ctor: required span size is not representable as index_type.");
if constexpr (__rank_ > 1) {
_LIBCPP_ASSERT_UNCATEGORIZED(
([&]<size_t... _Pos>(index_sequence<_Pos...>) {
// basically sort the dimensions based on strides and extents, sorting is represented in permute array
array<rank_type, __rank_> __permute{_Pos...};
__bubble_sort_by_strides(__permute);
// check that this permutations represents a growing set
for (rank_type __i = 1; __i < __rank_; __i++)
if (static_cast<index_type>(__strides[__permute[__i]]) <
static_cast<index_type>(__strides[__permute[__i - 1]]) * __extents_.extent(__permute[__i - 1]))
return false;
return true;
}(make_index_sequence<__rank_>())),
"layout_stride::mapping ctor: the provided extents and strides lead to a non-unique mapping");
}
}
template <class _OtherIndexType>
requires(is_convertible_v<const _OtherIndexType&, index_type> &&
is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
_LIBCPP_HIDE_FROM_ABI constexpr mapping(const extents_type& __ext,
const array<_OtherIndexType, __rank_>& __strides) noexcept
: mapping(__ext, span(__strides)) {}
template <class _StridedLayoutMapping>
requires(__mdspan_detail::__layout_mapping_alike<_StridedLayoutMapping> &&
is_constructible_v<extents_type, typename _StridedLayoutMapping::extents_type> &&
_StridedLayoutMapping::is_always_unique() && _StridedLayoutMapping::is_always_strided())
_LIBCPP_HIDE_FROM_ABI constexpr explicit(
!(is_convertible_v<typename _StridedLayoutMapping::extents_type, extents_type> &&
(__mdspan_detail::__is_mapping_of<layout_left, _StridedLayoutMapping> ||
__mdspan_detail::__is_mapping_of<layout_right, _StridedLayoutMapping> ||
__mdspan_detail::__is_mapping_of<layout_stride, _StridedLayoutMapping>)))
mapping(const _StridedLayoutMapping& __other) noexcept
: __extents_(__other.extents()), __strides_([&]<size_t... _Pos>(index_sequence<_Pos...>) {
// stride() only compiles for rank > 0
if constexpr (__rank_ > 0) {
return __mdspan_detail::__possibly_empty_array<index_type, __rank_>{
static_cast<index_type>(__other.stride(_Pos))...};
} else {
return __mdspan_detail::__possibly_empty_array<index_type, 0>{};
}
}(make_index_sequence<__rank_>())) {
// stride() only compiles for rank > 0
if constexpr (__rank_ > 0) {
_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
([&]<size_t... _Pos>(index_sequence<_Pos...>) {
return ((static_cast<index_type>(__other.stride(_Pos)) > static_cast<index_type>(0)) && ... && true);
}(make_index_sequence<__rank_>())),
"layout_stride::mapping converting ctor: all strides must be greater than 0");
}
_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
__mdspan_detail::__is_representable_as<index_type>(__other.required_span_size()),
"layout_stride::mapping converting ctor: other.required_span_size() must be representable as index_type.");
_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(static_cast<index_type>(0) == __offset(__other),
"layout_stride::mapping converting ctor: base offset of mapping must be zero.");
}
_LIBCPP_HIDE_FROM_ABI constexpr mapping& operator=(const mapping&) noexcept = default;
// [mdspan.layout.stride.obs], observers
_LIBCPP_HIDE_FROM_ABI constexpr const extents_type& extents() const noexcept { return __extents_; }
_LIBCPP_HIDE_FROM_ABI constexpr array<index_type, __rank_> strides() const noexcept {
return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
return array<index_type, __rank_>{__strides_[_Pos]...};
}(make_index_sequence<__rank_>());
}
_LIBCPP_HIDE_FROM_ABI constexpr index_type required_span_size() const noexcept {
if constexpr (__rank_ == 0) {
return static_cast<index_type>(1);
} else {
return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
if ((__extents_.extent(_Pos) * ... * 1) == 0)
return static_cast<index_type>(0);
else
return static_cast<index_type>(
static_cast<index_type>(1) +
(((__extents_.extent(_Pos) - static_cast<index_type>(1)) * __strides_[_Pos]) + ... +
static_cast<index_type>(0)));
}(make_index_sequence<__rank_>());
}
}
template <class... _Indices>
requires((sizeof...(_Indices) == __rank_) && (is_convertible_v<_Indices, index_type> && ...) &&
(is_nothrow_constructible_v<index_type, _Indices> && ...))
_LIBCPP_HIDE_FROM_ABI constexpr index_type operator()(_Indices... __idx) const noexcept {
// Mappings are generally meant to be used for accessing allocations and are meant to guarantee to never
// return a value exceeding required_span_size(), which is used to know how large an allocation one needs
// Thus, this is a canonical point in multi-dimensional data structures to make invalid element access checks
// However, mdspan does check this on its own, so for now we avoid double checking in hardened mode
_LIBCPP_ASSERT_UNCATEGORIZED(__mdspan_detail::__is_multidimensional_index_in(__extents_, __idx...),
"layout_stride::mapping: out of bounds indexing");
return [&]<size_t... _Pos>(index_sequence<_Pos...>) {
return ((static_cast<index_type>(__idx) * __strides_[_Pos]) + ... + index_type(0));
}(make_index_sequence<sizeof...(_Indices)>());
}
_LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_unique() noexcept { return true; }
_LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_exhaustive() noexcept { return false; }
_LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_strided() noexcept { return true; }
_LIBCPP_HIDE_FROM_ABI static constexpr bool is_unique() noexcept { return true; }
// The answer of this function is fairly complex in the case where one or more
// extents are zero.
// Technically it is meaningless to query is_exhaustive() in that case, but unfortunately
// the way the standard defines this function, we can't give a simple true or false then.
_LIBCPP_HIDE_FROM_ABI constexpr bool is_exhaustive() const noexcept {
if constexpr (__rank_ == 0)
return true;
else {
index_type __span_size = required_span_size();
if (__span_size == static_cast<index_type>(0)) {
if constexpr (__rank_ == 1)
return __strides_[0] == 1;
else {
rank_type __r_largest = 0;
for (rank_type __r = 1; __r < __rank_; __r++)
if (__strides_[__r] > __strides_[__r_largest])
__r_largest = __r;
for (rank_type __r = 0; __r < __rank_; __r++)
if (__extents_.extent(__r) == 0 && __r != __r_largest)
return false;
return true;
}
} else {
return required_span_size() == [&]<size_t... _Pos>(index_sequence<_Pos...>) {
return (__extents_.extent(_Pos) * ... * static_cast<index_type>(1));
}(make_index_sequence<__rank_>());
}
}
}
_LIBCPP_HIDE_FROM_ABI static constexpr bool is_strided() noexcept { return true; }
// according to the standard layout_stride does not have a constraint on stride(r) for rank>0
// it still has the precondition though
_LIBCPP_HIDE_FROM_ABI constexpr index_type stride(rank_type __r) const noexcept {
_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__r < __rank_, "layout_stride::mapping::stride(): invalid rank index");
return __strides_[__r];
}
template <class _OtherMapping>
requires(__mdspan_detail::__layout_mapping_alike<_OtherMapping> &&
(_OtherMapping::extents_type::rank() == __rank_) && _OtherMapping::is_always_strided())
_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const mapping& __lhs, const _OtherMapping& __rhs) noexcept {
if (__offset(__rhs))
return false;
if constexpr (__rank_ == 0)
return true;
else {
return __lhs.extents() == __rhs.extents() && [&]<size_t... _Pos>(index_sequence<_Pos...>) {
// avoid warning when comparing signed and unsigner integers and pick the wider of two types
using _CommonType = common_type_t<index_type, typename _OtherMapping::index_type>;
return ((static_cast<_CommonType>(__lhs.stride(_Pos)) == static_cast<_CommonType>(__rhs.stride(_Pos))) && ... &&
true);
}(make_index_sequence<__rank_>());
}
}
private:
_LIBCPP_NO_UNIQUE_ADDRESS extents_type __extents_{};
_LIBCPP_NO_UNIQUE_ADDRESS __mdspan_detail::__possibly_empty_array<index_type, __rank_> __strides_{};
};
#endif // _LIBCPP_STD_VER >= 23
_LIBCPP_END_NAMESPACE_STD
_LIBCPP_POP_MACROS
#endif // _LIBCPP___MDSPAN_LAYOUT_STRIDE_H
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