3 files changed, 131 insertions, 0 deletions
diff --git a/asl/handle_pool/BUILD.bazel b/asl/handle_pool/BUILD.bazel
new file mode 100644
index 0000000..e5048d3
--- /dev/null
+++ b/asl/handle_pool/BUILD.bazel
@@ -0,0 +1,33 @@
+# Copyright 2025 Steven Le Rouzic
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+package(
+    default_applicable_licenses = ["//:license"],
+)
+
+cc_library(
+    name = "index_pool",
+    hdrs = [
+        "index_pool.hpp",
+    ],
+    deps = [
+        "//asl/memory",
+        "//asl/memory:allocator",
+        "//asl/base",
+        "//asl/containers:chunked_buffer",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+cc_test(
+    name = "index_pool_tests",
+    srcs = [
+        "index_pool_tests.cpp",
+    ],
+    deps = [
+        ":index_pool",
+        "//asl/tests:utils",
+        "//asl/testing",
+    ],
+)
diff --git a/asl/handle_pool/index_pool.hpp b/asl/handle_pool/index_pool.hpp
new file mode 100644
index 0000000..377f6f4
--- /dev/null
+++ b/asl/handle_pool/index_pool.hpp
@@ -0,0 +1,88 @@
+// Copyright 2025 Steven Le Rouzic
+//
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "asl/base/integers.hpp"
+#include "asl/base/meta.hpp"
+#include "asl/containers/chunked_buffer.hpp"
+#include "asl/memory/allocator.hpp"
+
+namespace asl
+{
+
+template<
+    int kIndexSize_,
+    int kGenSize_,
+    int kUserSize_ = 0
+>
+requires (
+    kUserSize_ >= 0
+    && kGenSize_ > 0
+    && kIndexSize_ > 0
+    && (kUserSize_ + kGenSize_ + kIndexSize_ <= 63)
+)
+struct index_pool_config
+{
+    static constexpr int kUserSize  = kUserSize_;
+    static constexpr int kGenSize   = kGenSize_;
+    static constexpr int kIndexSize = kIndexSize_;
+
+    static constexpr bool kHasUser  = kUserSize > 0;
+
+    using handle_type = smallest_unsigned_integer_type_for_width<kGenSize + kIndexSize + kUserSize>;
+    using user_type   = select_t<kHasUser, smallest_unsigned_integer_type_for_width<kUserSize>, empty>;
+};
+
+
+template<
+    int kIndexSize_,
+    int kGenSize_,
+    typename UserType = empty,
+    int kUserSize_ = 0
+>
+requires (
+    same_as<UserType, empty> || (kUserSize_ <= size_of<UserType> * 8 && trivially_copy_constructible<UserType>)
+)
+class index_pool_handle_base
+{
+    static constexpr int kUserSizeComputed =
+        same_as<UserType, empty> ? 0 : (kUserSize_ == 0 ? size_of<UserType> * 8 : kUserSize_); // NOLINT
+
+public:
+    using config = index_pool_config<kIndexSize_, kGenSize_, kUserSizeComputed>;
+
+private:
+    using handle_type        = config::handle_type;
+    using user_type          = config::user_type;
+    using user_type_external = UserType;
+    
+    static constexpr handle_type kHasValueMask = ~(~handle_type{0} >> 1);
+
+    static constexpr handle_type kIndexMask = (handle_type{1} << config::kIndexSize) - 1;
+
+    static constexpr int         kGenShift = config::kIndexSize;
+    static constexpr handle_type kGenMask  = ((handle_type{1} << config::kGenSize) - 1) << kGenShift;
+
+    static constexpr int         kUserShift = config::kIndexSize + config::kGenSize;
+    static constexpr handle_type kUserMask  = ((handle_type{1} << config::kUserSize) - 1) << kUserShift;
+                                        
+    handle_type m_handle{};
+
+public:
+    [[nodiscard]] constexpr bool has_value() const { return m_handle & kHasValueMask; }
+
+    [[nodiscard]] constexpr user_type_external user() const
+        requires config::kHasUser
+    {
+        return bit_cast<user_type_external>(
+            static_cast<user_type>((m_handle & kUserMask) >> kUserShift)
+        );
+    }
+};
+
+class IndexPool
+{
+};
+
+} // namespace asl
+
diff --git a/asl/handle_pool/index_pool_tests.cpp b/asl/handle_pool/index_pool_tests.cpp
new file mode 100644
index 0000000..1dd2816
--- /dev/null
+++ b/asl/handle_pool/index_pool_tests.cpp
@@ -0,0 +1,10 @@
+// Copyright 2025 Steven Le Rouzic
+//
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "asl/testing/testing.hpp"
+
+ASL_TEST(test)
+{
+}
+