add temp arenas

alloc.d

@@ -31,7 +31,14 @@ struct Arena
 	SLList!(ArenaPool) pools;
 	u64                pool_length;
 	u64                length;
-};
+}
+
+struct TempArena
+{
+	Arena*            arena;
+	Node!(ArenaPool)* start_node;
+	u64               start_pos;
+}
 
 T*
 MAlloc(T)()
@@ -93,8 +100,61 @@ CreateArena(u64 size)
 	AddArenaPool(&arena);
 
 	return arena;
+}
+
+TempArena
+BeginTempArena(Arena* arena)
+{
+	TempArena t = {
+		arena: arena,
 	};
 
+	auto n = arena.pools.first;
+	for(;;)
+	{
+		if(n.next == null)
+		{
+			t.start_node = n;
+			t.start_pos  = n.value.pos;
+			break;
+		}
+
+		n = n.next;
+	}
+
+	return t;
+}
+
+void
+End(TempArena* t)
+{
+	bool resetting = false;
+	for(auto n = t.arena.pools.first; n != null; n = n.next)
+	{
+		if(t.start_node == n)
+		{
+			n.value.pos = t.start_pos;
+			resetting = true;
+		}
+		else if(resetting)
+		{
+			n.value.pos = 0;
+		}
+	}
+}
+
+T[]
+AllocArray(T)(TempArena* t, u64 count)
+{
+	return AllocArray!(T)(t.arena, count);
+}
+
+T*
+Alloc(T)(TempArena* t)
+{
+	return Alloc!(T)(t.arena);
+}
+
 void
 AddArenaPool(Arena* arena)
 {