early-access version 1272

src/common/parent_of_member.h

@@ -0,0 +1,204 @@
+/*
+ * Copyright (c) 2018-2020 Atmosph<70>re-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <type_traits>
+
+#include "common/assert.h"
+#include "common/common_types.h"
+
+namespace Common {
+
+template <typename T, size_t Size, size_t Align>
+struct TypedStorage {
+    typename std::aligned_storage<Size, Align>::type _storage;
+};
+
+#define TYPED_STORAGE(...) TypedStorage<__VA_ARGS__, sizeof(__VA_ARGS__), alignof(__VA_ARGS__)>
+
+template <typename T>
+static constexpr T* GetPointer(TYPED_STORAGE(T) & ts) {
+    return static_cast<T*>(static_cast<void*>(std::addressof(ts._storage)));
+}
+
+template <typename T>
+static constexpr const T* GetPointer(const TYPED_STORAGE(T) & ts) {
+    return static_cast<const T*>(static_cast<const void*>(std::addressof(ts._storage)));
+}
+
+namespace impl {
+
+template <size_t MaxDepth>
+struct OffsetOfUnionHolder {
+    template <typename ParentType, typename MemberType, size_t Offset>
+    union UnionImpl {
+        using PaddingMember = char;
+        static constexpr size_t GetOffset() {
+            return Offset;
+        }
+
+#pragma pack(push, 1)
+        struct {
+            PaddingMember padding[Offset];
+            MemberType members[(sizeof(ParentType) / sizeof(MemberType)) + 1];
+        } data;
+#pragma pack(pop)
+        UnionImpl<ParentType, MemberType, Offset + 1> next_union;
+    };
+
+    template <typename ParentType, typename MemberType>
+    union UnionImpl<ParentType, MemberType, 0> {
+        static constexpr size_t GetOffset() {
+            return 0;
+        }
+
+        struct {
+            MemberType members[(sizeof(ParentType) / sizeof(MemberType)) + 1];
+        } data;
+        UnionImpl<ParentType, MemberType, 1> next_union;
+    };
+
+    template <typename ParentType, typename MemberType>
+    union UnionImpl<ParentType, MemberType, MaxDepth> { /* Empty ... */
+    };
+};
+
+template <typename ParentType, typename MemberType>
+struct OffsetOfCalculator {
+    using UnionHolder =
+        typename OffsetOfUnionHolder<sizeof(MemberType)>::template UnionImpl<ParentType, MemberType,
+                                                                             0>;
+    union Union {
+        char c;
+        UnionHolder first_union;
+        TYPED_STORAGE(ParentType) parent;
+
+        /* This coerces the active member to be c. */
+        constexpr Union() : c() { /* ... */
+        }
+    };
+    static constexpr Union U = {};
+
+    static constexpr const MemberType* GetNextAddress(const MemberType* start,
+                                                      const MemberType* target) {
+        while (start < target) {
+            start++;
+        }
+        return start;
+    }
+
+    static constexpr std::ptrdiff_t GetDifference(const MemberType* start,
+                                                  const MemberType* target) {
+        return (target - start) * sizeof(MemberType);
+    }
+
+    template <typename CurUnion>
+    static constexpr std::ptrdiff_t OffsetOfImpl(MemberType ParentType::*member,
+                                                 CurUnion& cur_union) {
+        constexpr size_t Offset = CurUnion::GetOffset();
+        const auto target = std::addressof(GetPointer(U.parent)->*member);
+        const auto start = std::addressof(cur_union.data.members[0]);
+        const auto next = GetNextAddress(start, target);
+
+        if (next != target) {
+            if constexpr (Offset < sizeof(MemberType) - 1) {
+                return OffsetOfImpl(member, cur_union.next_union);
+            } else {
+                UNREACHABLE();
+            }
+        }
+
+        return (next - start) * sizeof(MemberType) + Offset;
+    }
+
+    static constexpr std::ptrdiff_t OffsetOf(MemberType ParentType::*member) {
+        return OffsetOfImpl(member, U.first_union);
+    }
+};
+
+template <typename T>
+struct GetMemberPointerTraits;
+
+template <typename P, typename M>
+struct GetMemberPointerTraits<M P::*> {
+    using Parent = P;
+    using Member = M;
+};
+
+template <auto MemberPtr>
+using GetParentType = typename GetMemberPointerTraits<decltype(MemberPtr)>::Parent;
+
+template <auto MemberPtr>
+using GetMemberType = typename GetMemberPointerTraits<decltype(MemberPtr)>::Member;
+
+template <auto MemberPtr, typename RealParentType = GetParentType<MemberPtr>>
+static inline std::ptrdiff_t OffsetOf = [] {
+    using DeducedParentType = GetParentType<MemberPtr>;
+    using MemberType = GetMemberType<MemberPtr>;
+    static_assert(std::is_base_of<DeducedParentType, RealParentType>::value ||
+                  std::is_same<RealParentType, DeducedParentType>::value);
+
+    return OffsetOfCalculator<RealParentType, MemberType>::OffsetOf(MemberPtr);
+}();
+
+} // namespace impl
+
+template <auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
+constexpr RealParentType& GetParentReference(impl::GetMemberType<MemberPtr>* member) {
+    std::ptrdiff_t Offset = impl::OffsetOf<MemberPtr, RealParentType>;
+    return *static_cast<RealParentType*>(
+        static_cast<void*>(static_cast<uint8_t*>(static_cast<void*>(member)) - Offset));
+}
+
+template <auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
+constexpr RealParentType const& GetParentReference(impl::GetMemberType<MemberPtr> const* member) {
+    std::ptrdiff_t Offset = impl::OffsetOf<MemberPtr, RealParentType>;
+    return *static_cast<const RealParentType*>(static_cast<const void*>(
+        static_cast<const uint8_t*>(static_cast<const void*>(member)) - Offset));
+}
+
+template <auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
+constexpr RealParentType* GetParentPointer(impl::GetMemberType<MemberPtr>* member) {
+    return std::addressof(GetParentReference<MemberPtr, RealParentType>(member));
+}
+
+template <auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
+constexpr RealParentType const* GetParentPointer(impl::GetMemberType<MemberPtr> const* member) {
+    return std::addressof(GetParentReference<MemberPtr, RealParentType>(member));
+}
+
+template <auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
+constexpr RealParentType& GetParentReference(impl::GetMemberType<MemberPtr>& member) {
+    return GetParentReference<MemberPtr, RealParentType>(std::addressof(member));
+}
+
+template <auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
+constexpr RealParentType const& GetParentReference(impl::GetMemberType<MemberPtr> const& member) {
+    return GetParentReference<MemberPtr, RealParentType>(std::addressof(member));
+}
+
+template <auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
+constexpr RealParentType* GetParentPointer(impl::GetMemberType<MemberPtr>& member) {
+    return std::addressof(GetParentReference<MemberPtr, RealParentType>(member));
+}
+
+template <auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
+constexpr RealParentType const* GetParentPointer(impl::GetMemberType<MemberPtr> const& member) {
+    return std::addressof(GetParentReference<MemberPtr, RealParentType>(member));
+}
+
+} // namespace Common