new macro 'intop' (to perform integer arithmetic on unsigned types)

lvm.h

@@ -1,5 +1,5 @@
 /*
-** $Id: lvm.h,v 2.21 2013/04/26 16:03:50 roberto Exp roberto $
+** $Id: lvm.h,v 2.22 2013/04/29 17:12:50 roberto Exp roberto $
 ** Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -21,6 +21,8 @@
 #define tointeger(o,i) \
 	(ttisinteger(o) ? (*(i) = ivalue(o), 1) : luaV_tointeger_(o,i))
 
+#define intop(op,v1,v2) \
+	cast_integer(cast_unsigned(v1) op cast_unsigned(v2))
 
 #define luaV_rawequalobj(t1,t2)		luaV_equalobj(NULL,t1,t2)