[common] Switch to boost::unordered_flat containers (#4326)

Replaces all instances of ankerl's unordered map/set with boost's
`unordered_flat_*` classes. This uses std::hash since boost::hash is
actually a lot slower.

Also adds an abstraction layer in `Common` so future changes are quicker
and easier.

Other implementation details:
- ankerl provided hash specializations for tuple and pair, so those were
  ported here
- std::erase_if doesn't work on boost, so just used the ADL'd erase_if

This should be about equal or superior performance as unordered_dense for everything except iteration.

Signed-off-by: crueter <crueter@eden-emu.dev>

- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md)
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.

-------------------

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4326
Reviewed-by: Lizzie and Samuel <lizzie@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

9 files changed, 81 insertions, 14 deletions

diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index 10e8cd0cc7..d90190e6a0 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -147,7 +147,8 @@ add_library(
     cpu_features.cpp
     cpu_features.h
     httplib.h
-    net/net.h net/net.cpp)
+    net/net.h net/net.cpp
+    container/unordered_map.h container/unordered_set.h)
 
 if(WIN32)
     target_sources(common PRIVATE windows/timer_resolution.cpp
@@ -241,7 +242,7 @@ if (lz4_ADDED)
     target_include_directories(common PRIVATE ${lz4_SOURCE_DIR}/lib)
 endif()
 
-target_link_libraries(common PUBLIC fmt::fmt stb::headers Threads::Threads unordered_dense::unordered_dense)
+target_link_libraries(common PUBLIC fmt::fmt stb::headers Threads::Threads)
 target_link_libraries(common PRIVATE lz4::lz4 zstd::zstd)
 
 # Please refer to src/common/demangle.cpp
diff --git a/src/common/container/unordered_map.h b/src/common/container/unordered_map.h
new file mode 100644
index 0000000000..7d9e49fd80
--- /dev/null
+++ b/src/common/container/unordered_map.h
@@ -0,0 +1,16 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include "common/container_hash.h"
+
+#include <boost/unordered/unordered_flat_map.hpp>
+
+namespace Common {
+
+template <class Key, class T, class Hash = std::hash<Key>, class Pred = std::equal_to<Key>,
+          class Allocator = std::allocator<std::pair<const Key, T>>>
+using unordered_map = boost::unordered::unordered_flat_map<Key, T, Hash, Pred, Allocator>;
+
+}
diff --git a/src/common/container/unordered_set.h b/src/common/container/unordered_set.h
new file mode 100644
index 0000000000..54d71406a1
--- /dev/null
+++ b/src/common/container/unordered_set.h
@@ -0,0 +1,16 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include "common/container_hash.h"
+
+#include <boost/unordered/unordered_flat_set.hpp>
+
+namespace Common {
+
+template <class Key, class Hash = std::hash<Key>, class Pred = std::equal_to<Key>,
+          class Allocator = std::allocator<Key>>
+using unordered_set = boost::unordered::unordered_flat_set<Key, Hash, Pred, Allocator>;
+
+}
diff --git a/src/common/container_hash.h b/src/common/container_hash.h
index b6d8e02e26..d7477f7e4f 100644
--- a/src/common/container_hash.h
+++ b/src/common/container_hash.h
@@ -10,8 +10,11 @@
 #include <array>
 #include <climits>
 #include <cstdint>
+#include <functional>
 #include <limits>
+#include <tuple>
 #include <type_traits>
+#include <utility>
 #include <vector>
 
 namespace Common {
@@ -69,10 +72,17 @@ struct HashCombineImpl<64> {
 } // namespace detail
 
 template <typename T>
+    requires std::is_unsigned_v<T>
 inline void HashCombine(std::size_t& seed, const T& v) {
     seed = detail::HashCombineImpl<sizeof(std::size_t) * CHAR_BIT>::fn(seed, detail::HashValue(v));
 }
 
+template <typename T>
+    requires (!std::is_unsigned_v<T>)
+inline void HashCombine(std::size_t& seed, const T& v) {
+    seed = detail::HashCombineImpl<sizeof(std::size_t) * CHAR_BIT>::fn(seed, std::hash<T>{}(v));
+}
+
 template <typename It>
 inline std::size_t HashRange(It first, It last) {
     std::size_t seed = 0;
@@ -95,3 +105,26 @@ std::size_t HashValue(const std::vector<T, Allocator>& v) {
 }
 
 } // namespace Common
+
+namespace std {
+
+template <typename... Args>
+struct hash<std::tuple<Args...>> {
+    std::size_t operator()(const std::tuple<Args...>& t) const noexcept {
+        std::size_t seed = 0;
+        std::apply([&seed](const Args&... args) { (Common::HashCombine(seed, args), ...); }, t);
+        return seed;
+    }
+};
+
+template <class A, class B>
+struct hash<std::pair<A, B>> {
+    std::size_t operator()(const std::pair<A, B>& p) const noexcept {
+        std::size_t seed = 0;
+        Common::HashCombine(seed, p.first);
+        Common::HashCombine(seed, p.second);
+        return seed;
+    }
+};
+
+} // namespace std
diff --git a/src/common/fs/path_util.cpp b/src/common/fs/path_util.cpp
index 9adf210ab7..b4c7eae343 100644
--- a/src/common/fs/path_util.cpp
+++ b/src/common/fs/path_util.cpp
@@ -7,7 +7,7 @@
 #include <algorithm>
 #include <iostream>
 #include <sstream>
-#include <ankerl/unordered_dense.h>
+#include "common/container/unordered_map.h"
 
 #include "common/assert.h"
 #include "common/fs/fs.h"
@@ -196,8 +196,8 @@ private:
         SetLegacyPathImpl(legacy_path, new_path);
     }
 
-    ankerl::unordered_dense::map<EdenPath, fs::path> eden_paths;
-    ankerl::unordered_dense::map<EmuPath, fs::path> legacy_paths;
+    ::Common::unordered_map<EdenPath, fs::path> eden_paths;
+    ::Common::unordered_map<EmuPath, fs::path> legacy_paths;
 };
 
 bool ValidatePath(const fs::path& path) {
diff --git a/src/common/host_memory.cpp b/src/common/host_memory.cpp
index 445d34c444..fa30b2c047 100644
--- a/src/common/host_memory.cpp
+++ b/src/common/host_memory.cpp
@@ -7,7 +7,7 @@
 #ifdef _WIN32
 
 #include <iterator>
-#include <ankerl/unordered_dense.h>
+#include "common/container/unordered_map.h"
 #include <boost/icl/separate_interval_set.hpp>
 #include <windows.h>
 #include "common/dynamic_library.h"
@@ -391,7 +391,7 @@ private:
 
     std::mutex placeholder_mutex;                                 ///< Mutex for placeholders
     boost::icl::separate_interval_set<size_t> placeholders;       ///< Mapped placeholders
-    ankerl::unordered_dense::map<size_t, size_t> placeholder_host_pointers; ///< Placeholder backing offset
+    ::Common::unordered_map<size_t, size_t> placeholder_host_pointers; ///< Placeholder backing offset
 };
 
 #elif defined(__OPENORBIS__) || defined(__managarm__)
diff --git a/src/common/input.h b/src/common/input.h
index bd9b2d1656..514f93b494 100644
--- a/src/common/input.h
+++ b/src/common/input.h
@@ -9,7 +9,7 @@
 #include <functional>
 #include <memory>
 #include <string>
-#include <ankerl/unordered_dense.h>
+#include "common/container/unordered_map.h"
 #include <utility>
 #include <vector>
 #include "common/logging.h"
@@ -412,7 +412,7 @@ public:
 namespace Impl {
 
 template <typename InputDeviceType>
-using FactoryListType = ankerl::unordered_dense::map<std::string, std::shared_ptr<Factory<InputDeviceType>>>;
+using FactoryListType = ::Common::unordered_map<std::string, std::shared_ptr<Factory<InputDeviceType>>>;
 
 template <typename InputDeviceType>
 struct FactoryList {
diff --git a/src/common/param_package.h b/src/common/param_package.h
index 0216863a39..5561dc1b7b 100644
--- a/src/common/param_package.h
+++ b/src/common/param_package.h
@@ -8,14 +8,14 @@
 
 #include <initializer_list>
 #include <string>
-#include <ankerl/unordered_dense.h>
+#include "common/container/unordered_map.h"
 
 namespace Common {
 
 /// A string-based key-value container supporting serializing to and deserializing from a string
 class ParamPackage {
 public:
-    using DataType = ankerl::unordered_dense::map<std::string, std::string>;
+    using DataType = ::Common::unordered_map<std::string, std::string>;
 
     ParamPackage() = default;
     explicit ParamPackage(const std::string& serialized);
diff --git a/src/common/x64/xbyak.h b/src/common/x64/xbyak.h
index 5288c5184f..11d3e2b184 100644
--- a/src/common/x64/xbyak.h
+++ b/src/common/x64/xbyak.h
@@ -22,10 +22,11 @@
 #endif
 
 // You must ensure this matches with src/common/x64/xbyak.h on root dir
-#include <ankerl/unordered_dense.h>
+#include "common/container/unordered_map.h"
+#include "common/container/unordered_set.h"
 #include <boost/unordered_map.hpp>
-#define XBYAK_STD_UNORDERED_SET ankerl::unordered_dense::set
-#define XBYAK_STD_UNORDERED_MAP ankerl::unordered_dense::map
+#define XBYAK_STD_UNORDERED_SET ::Common::unordered_set
+#define XBYAK_STD_UNORDERED_MAP ::Common::unordered_map
 #define XBYAK_STD_UNORDERED_MULTIMAP boost::unordered_multimap
 #include <xbyak/xbyak.h>
 #include <xbyak/xbyak_util.h>