Arena *alloc_arena(U64 cap)
{
	Arena	*a;

	/* TODO(pryazha): Use OS specific memory allocator
	 * (like VirtualAlloc on Windows or mmap on Linux)
	 */
	a = malloc(sizeof(Arena));
	ASSERT(a);

	if (!cap)
		cap = PRB_DEFAULT_ALLOC_SIZE;

	a->mem = malloc(cap);
	ASSERT(a->mem);
	a->cap = cap;
	a->used = 0;

	return a;
}

void release_arena(Arena *a)
{
	free(a->mem);
	MEM0STRUCT(a);
	free(a);
}

void *push_arena(Arena *a, U64 size)
{
	ASSERT(a);
	ASSERT(a->used+size <= a->cap);

	void	*r;

	r = a->mem+a->used;
	a->used += size;

	return r;
}

void pop_arena(Arena *a, U64 size)
{
	ASSERT(a);
	U64	clamped;
	clamped = CLAMPTOP(size, a->used);
	a->used = a->used-clamped;
}