Add arena to furlang

Signed-off-by: CHatingPython <chatingpython@gmail.com>

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