1 files changed, 47 insertions, 5 deletions
diff --git a/prb_arena.h b/prb_arena.h
index 2d3453f..0a6de9b 100644
--- a/prb_arena.h
+++ b/prb_arena.h
@@ -1,6 +1,48 @@
-#define PRB_DEFAULT_ALLOC_SIZE	KB(4)
+#define DEFAULT_ARENA_SIZE kilobytes(4)
 
-Arena	*alloc_arena(U64 cap);
-void	release_arena(Arena *a);
-void	*push_arena(Arena *a, U64 size);
-void	pop_arena(Arena *a, U64 size);
+arena_t	alloc_arena(u64 capacity)
+{
+	void *sys_alloc(u64 length);
+
+	/* TODO(pryazha): Find reasonable maximum capacity through testing */
+	assert(capacity <= (u64)gigabytes(16));
+
+	if (!capacity)
+		capacity = DEFAULT_ARENA_SIZE;
+
+	/* TODO(pryazha): Use OS specific memory allocator
+	 * (like VirtualAlloc on Windows or mmap on Linux)
+	 */
+	void *memory = sys_alloc(capacity);
+	assert(memory);
+
+	arena_t arena = {memory, capacity, 0};
+
+	return arena;
+}
+
+void release_arena(arena_t *arena)
+{
+	void sys_free(void *memory, u64 length);
+
+	assert(arena);
+	sys_free(arena->memory, arena->capacity);
+	arena->memory = 0;
+	arena->capacity = 0;
+	arena->used = 0;
+}
+
+void *push_arena(arena_t *arena, u64 size)
+{
+	assert(arena);
+	assert(arena->used + size <= arena->capacity);
+	void *memory = arena->memory + arena->used;
+	arena->used += size;
+	return memory;
+}
+
+void pop_arena(arena_t *arena, u64 size)
+{
+	assert(arena);
+	arena->used -= min(size, arena->used);
+}