2 files changed, 228 insertions, 0 deletions

diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index 85926fc8f..bf3f3b781 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -121,6 +121,7 @@ add_library(common STATIC
     settings_input.cpp
     settings_input.h
     settings_setting.h
+    slot_vector.h
     socket_types.h
     spin_lock.cpp
     spin_lock.h
diff --git a/src/common/slot_vector.h b/src/common/slot_vector.h
new file mode 100644
index 000000000..34ff7de94
--- /dev/null
+++ b/src/common/slot_vector.h
@@ -0,0 +1,227 @@
+// SPDX-FileCopyrightText: Copyright 2020 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <algorithm>
+#include <bit>
+#include <numeric>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include "common/assert.h"
+#include "common/common_types.h"
+#include "common/polyfill_ranges.h"
+
+namespace Common {
+
+struct SlotId {
+    static constexpr u32 INVALID_INDEX = std::numeric_limits<u32>::max();
+
+    constexpr auto operator<=>(const SlotId&) const noexcept = default;
+
+    constexpr explicit operator bool() const noexcept {
+        return index != INVALID_INDEX;
+    }
+
+    u32 index = INVALID_INDEX;
+};
+
+template <class T>
+    requires std::is_nothrow_move_assignable_v<T> && std::is_nothrow_move_constructible_v<T>
+class SlotVector {
+public:
+    class Iterator {
+        friend SlotVector<T>;
+
+    public:
+        constexpr Iterator() = default;
+
+        Iterator& operator++() noexcept {
+            const u64* const bitset = slot_vector->stored_bitset.data();
+            const u32 size = static_cast<u32>(slot_vector->stored_bitset.size()) * 64;
+            if (id.index < size) {
+                do {
+                    ++id.index;
+                } while (id.index < size && !IsValid(bitset));
+                if (id.index == size) {
+                    id.index = SlotId::INVALID_INDEX;
+                }
+            }
+            return *this;
+        }
+
+        Iterator operator++(int) noexcept {
+            const Iterator copy{*this};
+            ++*this;
+            return copy;
+        }
+
+        bool operator==(const Iterator& other) const noexcept {
+            return id.index == other.id.index;
+        }
+
+        bool operator!=(const Iterator& other) const noexcept {
+            return id.index != other.id.index;
+        }
+
+        std::pair<SlotId, T*> operator*() const noexcept {
+            return {id, std::addressof((*slot_vector)[id])};
+        }
+
+        T* operator->() const noexcept {
+            return std::addressof((*slot_vector)[id]);
+        }
+
+    private:
+        Iterator(SlotVector<T>* slot_vector_, SlotId id_) noexcept
+            : slot_vector{slot_vector_}, id{id_} {}
+
+        bool IsValid(const u64* bitset) const noexcept {
+            return ((bitset[id.index / 64] >> (id.index % 64)) & 1) != 0;
+        }
+
+        SlotVector<T>* slot_vector;
+        SlotId id;
+    };
+
+    ~SlotVector() noexcept {
+        size_t index = 0;
+        for (u64 bits : stored_bitset) {
+            for (size_t bit = 0; bits; ++bit, bits >>= 1) {
+                if ((bits & 1) != 0) {
+                    values[index + bit].object.~T();
+                }
+            }
+            index += 64;
+        }
+        delete[] values;
+    }
+
+    [[nodiscard]] T& operator[](SlotId id) noexcept {
+        ValidateIndex(id);
+        return values[id.index].object;
+    }
+
+    [[nodiscard]] const T& operator[](SlotId id) const noexcept {
+        ValidateIndex(id);
+        return values[id.index].object;
+    }
+
+    template <typename... Args>
+    [[nodiscard]] SlotId insert(Args&&... args) noexcept {
+        const u32 index = FreeValueIndex();
+        new (&values[index].object) T(std::forward<Args>(args)...);
+        SetStorageBit(index);
+
+        return SlotId{index};
+    }
+
+    void erase(SlotId id) noexcept {
+        values[id.index].object.~T();
+        free_list.push_back(id.index);
+        ResetStorageBit(id.index);
+    }
+
+    [[nodiscard]] Iterator begin() noexcept {
+        const auto it = std::ranges::find_if(stored_bitset, [](u64 value) { return value != 0; });
+        if (it == stored_bitset.end()) {
+            return end();
+        }
+        const u32 word_index = static_cast<u32>(std::distance(it, stored_bitset.begin()));
+        const SlotId first_id{word_index * 64 + static_cast<u32>(std::countr_zero(*it))};
+        return Iterator(this, first_id);
+    }
+
+    [[nodiscard]] Iterator end() noexcept {
+        return Iterator(this, SlotId{SlotId::INVALID_INDEX});
+    }
+
+    [[nodiscard]] size_t size() const noexcept {
+        return values_capacity - free_list.size();
+    }
+
+private:
+    struct NonTrivialDummy {
+        NonTrivialDummy() noexcept {}
+    };
+
+    union Entry {
+        Entry() noexcept : dummy{} {}
+        ~Entry() noexcept {}
+
+        NonTrivialDummy dummy;
+        T object;
+    };
+
+    void SetStorageBit(u32 index) noexcept {
+        stored_bitset[index / 64] |= u64(1) << (index % 64);
+    }
+
+    void ResetStorageBit(u32 index) noexcept {
+        stored_bitset[index / 64] &= ~(u64(1) << (index % 64));
+    }
+
+    bool ReadStorageBit(u32 index) noexcept {
+        return ((stored_bitset[index / 64] >> (index % 64)) & 1) != 0;
+    }
+
+    void ValidateIndex(SlotId id) const noexcept {
+        DEBUG_ASSERT(id);
+        DEBUG_ASSERT(id.index / 64 < stored_bitset.size());
+        DEBUG_ASSERT(((stored_bitset[id.index / 64] >> (id.index % 64)) & 1) != 0);
+    }
+
+    [[nodiscard]] u32 FreeValueIndex() noexcept {
+        if (free_list.empty()) {
+            Reserve(values_capacity ? (values_capacity << 1) : 1);
+        }
+        const u32 free_index = free_list.back();
+        free_list.pop_back();
+        return free_index;
+    }
+
+    void Reserve(size_t new_capacity) noexcept {
+        Entry* const new_values = new Entry[new_capacity];
+        size_t index = 0;
+        for (u64 bits : stored_bitset) {
+            for (size_t bit = 0; bits; ++bit, bits >>= 1) {
+                const size_t i = index + bit;
+                if ((bits & 1) == 0) {
+                    continue;
+                }
+                T& old_value = values[i].object;
+                new (&new_values[i].object) T(std::move(old_value));
+                old_value.~T();
+            }
+            index += 64;
+        }
+
+        stored_bitset.resize((new_capacity + 63) / 64);
+
+        const size_t old_free_size = free_list.size();
+        free_list.resize(old_free_size + (new_capacity - values_capacity));
+        std::iota(free_list.begin() + old_free_size, free_list.end(),
+                  static_cast<u32>(values_capacity));
+
+        delete[] values;
+        values = new_values;
+        values_capacity = new_capacity;
+    }
+
+    Entry* values = nullptr;
+    size_t values_capacity = 0;
+
+    std::vector<u64> stored_bitset;
+    std::vector<u32> free_list;
+};
+
+} // namespace Common
+
+template <>
+struct std::hash<Common::SlotId> {
+    size_t operator()(const Common::SlotId& id) const noexcept {
+        return std::hash<u32>{}(id.index);
+    }
+};