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| 1 | //===-- include/flang/Common/static-multimap-view.h -------------*- C++ -*-===// |
|---|---|
| 2 | // |
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | // See https://llvm.org/LICENSE.txt for license information. |
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | // |
| 7 | //===----------------------------------------------------------------------===// |
| 8 | |
| 9 | #ifndef FORTRAN_COMMON_STATIC_MULTIMAP_VIEW_H_ |
| 10 | #define FORTRAN_COMMON_STATIC_MULTIMAP_VIEW_H_ |
| 11 | #include <algorithm> |
| 12 | #include <utility> |
| 13 | |
| 14 | /// StaticMultimapView is a constexpr friendly multimap implementation over |
| 15 | /// sorted constexpr arrays. As the View name suggests, it does not duplicate |
| 16 | /// the sorted array but only brings range and search concepts over it. It |
| 17 | /// mainly erases the array size from the type and ensures the array is sorted |
| 18 | /// at compile time. When C++20 brings std::span and constexpr std::is_sorted, |
| 19 | /// this can most likely be replaced by those. |
| 20 | |
| 21 | namespace Fortran::common { |
| 22 | |
| 23 | template <typename V> class StaticMultimapView { |
| 24 | public: |
| 25 | using Key = typename V::Key; |
| 26 | using const_iterator = const V *; |
| 27 | |
| 28 | constexpr const_iterator begin() const { return begin_; } |
| 29 | constexpr const_iterator end() const { return end_; } |
| 30 | // Be sure to static_assert(map.Verify(), "must be sorted"); for |
| 31 | // every instance constexpr created. Sadly this cannot be done in |
| 32 | // the ctor since there is no way to know whether the ctor is actually |
| 33 | // called at compile time or not. |
| 34 | template <std::size_t N> |
| 35 | constexpr StaticMultimapView(const V (&array)[N]) |
| 36 | : begin_{&array[0]}, end_{&array[0] + N} {} |
| 37 | |
| 38 | // std::equal_range will be constexpr in C++20 only, so far there is actually |
| 39 | // no need for equal_range to be constexpr anyway. |
| 40 | std::pair<const_iterator, const_iterator> equal_range(const Key &key) const { |
| 41 | return std::equal_range(begin_, end_, key); |
| 42 | } |
| 43 | |
| 44 | // Check that the array is sorted. This used to assert at compile time that |
| 45 | // the array is indeed sorted. When C++20 is required for flang, |
| 46 | // std::is_sorted can be used here since it will be constexpr. |
| 47 | constexpr bool Verify() const { |
| 48 | const V *lastSeen{begin_}; |
| 49 | bool isSorted{true}; |
| 50 | for (const auto *x{begin_}; x != end_; ++x) { |
| 51 | isSorted &= lastSeen->key <= x->key; |
| 52 | lastSeen = x; |
| 53 | } |
| 54 | return isSorted; |
| 55 | } |
| 56 | |
| 57 | private: |
| 58 | const_iterator begin_{nullptr}; |
| 59 | const_iterator end_{nullptr}; |
| 60 | }; |
| 61 | } // namespace Fortran::common |
| 62 | #endif // FORTRAN_COMMON_STATIC_MULTIMAP_VIEW_H_ |
| 63 |
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