-XBT_PUBLIC(void*) xbt_swag_remove(void *obj, xbt_swag_t swag);
-XBT_PUBLIC(void*)xbt_swag_extract(xbt_swag_t swag);
-XBT_PUBLIC(int) xbt_swag_size(xbt_swag_t swag);
-XBT_PUBLIC(int) xbt_swag_belongs(void *obj, xbt_swag_t swag);
+XBT_PUBLIC(void *) xbt_swag_remove(void *obj, xbt_swag_t swag);
+XBT_PUBLIC(void *) xbt_swag_extract(xbt_swag_t swag);
+XBT_PUBLIC(int) xbt_swag_size(const_xbt_swag_t swag);
+
+#define xbt_swag_getPrev(obj, offset) (((xbt_swag_hookup_t)(((char *) (obj)) + (offset)))->prev)
+#define xbt_swag_getNext(obj, offset) (((xbt_swag_hookup_t)(((char *) (obj)) + (offset)))->next)
+#define xbt_swag_belongs(obj, swag) (xbt_swag_getNext((obj), (swag)->offset) || (swag)->tail == (obj))