#define PTR_TO(s, i) &((s*)0)->i
#define OFFSETOF(s, i) ((unsigned int) PTR_TO(s, i))
#define SKIP_BACK(s, i, p) ((s *)((char *)p - OFFSETOF(s, i)))
#define PTR_TO(s, i) &((s*)0)->i
#define OFFSETOF(s, i) ((unsigned int) PTR_TO(s, i))
#define SKIP_BACK(s, i, p) ((s *)((char *)p - OFFSETOF(s, i)))