From d2cfbb676327ba277c995ac108e178cd141752ef Mon Sep 17 00:00:00 2001
From: CHatingPython <real.catdev@gmail.com>
Date: Mon, 25 May 2026 14:59:42 +0200
Subject: [PATCH] Add arena to furlang

Signed-off-by: CHatingPython <chatingpython@gmail.com>
---
 furc/CMakeLists.txt               |  1 +
 furlang/CMakeLists.txt            |  4 ++
 furlang/include/furlang/arena.hpp | 48 ++++++++++++++++++++
 furlang/src/arena.cpp             | 75 +++++++++++++++++++++++++++++++
 4 files changed, 128 insertions(+)
 create mode 100644 furlang/include/furlang/arena.hpp
 create mode 100644 furlang/src/arena.cpp

diff --git a/furc/CMakeLists.txt b/furc/CMakeLists.txt
index ce04753..e89257e 100644
--- a/furc/CMakeLists.txt
+++ b/furc/CMakeLists.txt
@@ -4,6 +4,7 @@ add_library(libfurc ${FURC_SRCS} ${FURC_HDRS})
 target_include_directories(libfurc PUBLIC include/)
 target_compile_definitions(libfurc PRIVATE LIBFURC)
 set_target_properties(libfurc PROPERTIES PREFIX "")
+target_link_libraries(libfurc PUBLIC furlang)
 add_executable(furc src/main.cpp)
 target_link_libraries(furc PRIVATE libfurc)
 
diff --git a/furlang/CMakeLists.txt b/furlang/CMakeLists.txt
index e69de29..dd9a48b 100644
--- a/furlang/CMakeLists.txt
+++ b/furlang/CMakeLists.txt
@@ -0,0 +1,4 @@
+file(GLOB_RECURSE FURLANG_SRCS "src/**.cpp")
+file(GLOB_RECURSE FURLANG_HDRS "include/**.hpp")
+add_library(furlang STATIC ${FURLANG_SRCS} ${FURLANG_HDRS})
+target_include_directories(furlang PUBLIC include/)
\ No newline at end of file
diff --git a/furlang/include/furlang/arena.hpp b/furlang/include/furlang/arena.hpp
new file mode 100644
index 0000000..857146c
--- /dev/null
+++ b/furlang/include/furlang/arena.hpp
@@ -0,0 +1,48 @@
+#ifndef FURLANG_ARENA_HPP
+#define FURLANG_ARENA_HPP
+
+#include <cstddef>
+#include <cstdint>
+
+namespace furlang {
+
+class arena {
+private:
+    struct region {
+        using value_type = std::uintptr_t;
+
+        static region* create(std::size_t capacity);
+
+        region*     next;
+        std::size_t capacity;
+        std::size_t used;
+        value_type  storage[];
+
+        std::size_t free() const { return capacity - used; }
+    };
+public:
+    arena(std::size_t minCapacity = 4 * 1024ULL);
+    ~arena();
+
+    arena(arena&& other) noexcept;
+    arena(const arena&) = delete;
+    arena& operator=(arena&& other) noexcept;
+    arena& operator=(const arena&) = delete;
+public:
+    template <typename T>
+    T* allocate(std::size_t count = 1) {
+        return reinterpret_cast<T*>(allocate(sizeof(T), count));
+    }
+
+    void reset();
+private:
+    void* allocate(std::size_t size, std::size_t count);
+private:
+    std::size_t m_minCapacity;
+    region*     m_head = nullptr;
+    region*     m_tail = nullptr;
+};
+
+} // namespace furlang
+
+#endif // FURLANG_ARENA_HPP
\ No newline at end of file
diff --git a/furlang/src/arena.cpp b/furlang/src/arena.cpp
new file mode 100644
index 0000000..5863483
--- /dev/null
+++ b/furlang/src/arena.cpp
@@ -0,0 +1,75 @@
+#include "furlang/arena.hpp"
+
+#include <algorithm>
+#include <cstdlib>
+
+namespace furlang {
+
+arena::region* arena::region::create(std::size_t capacity) {
+    arena::region* region =
+        reinterpret_cast<arena::region*>(std::malloc(sizeof(*region) + (sizeof(value_type) * capacity))); // NOLINT
+    if (region == nullptr) return nullptr;
+    region->next     = nullptr;
+    region->capacity = capacity;
+    region->used     = 0;
+    return region;
+}
+
+arena::arena(std::size_t minCapacity)
+  : m_minCapacity(minCapacity) {}
+
+arena::~arena() {
+    region* next = nullptr;
+    for (region* region = m_head; region != nullptr; region = next) {
+        next = region->next;
+        delete region;
+    }
+}
+
+arena::arena(arena&& other) noexcept
+  : m_minCapacity(other.m_minCapacity), m_head(other.m_head), m_tail(other.m_tail) {
+    other.m_minCapacity = 0;
+    other.m_head        = nullptr;
+    other.m_tail        = nullptr;
+}
+
+arena& arena::operator=(arena&& other) noexcept {
+    if (this == &other) return *this;
+    m_minCapacity       = other.m_minCapacity;
+    m_head              = other.m_head;
+    m_tail              = other.m_tail;
+    other.m_minCapacity = 0;
+    other.m_head        = nullptr;
+    other.m_tail        = nullptr;
+    return *this;
+}
+
+void arena::reset() {
+    for (region* region = m_head; region != nullptr; region = region->next) {
+        region->used = 0;
+    }
+}
+
+void* arena::allocate(std::size_t size, std::size_t count) {
+    std::size_t sizeInBytes = size * count;
+    std::size_t sizeInWords = (sizeInBytes + sizeof(region::value_type) - 1) / sizeof(region::value_type);
+
+    if (m_head == nullptr) {
+        m_head = m_tail = region::create(std::min(sizeInWords, m_minCapacity));
+    }
+
+    region* region = m_head;
+    while (region != nullptr && region->free() < sizeInWords)
+        region = region->next;
+
+    if (region == nullptr) {
+        region = region::create(std::min(sizeInWords, m_minCapacity));
+        m_tail = m_tail->next = region;
+    }
+
+    uintptr_t* allocated = &region->storage[region->used];
+    region->used        += sizeInWords;
+    return allocated;
+}
+
+} // namespace furlang
\ No newline at end of file