SLP_FLAGS
#define slp_get_overflow(h) ((h)[SLP_FLAGS] & SLP_OVERFLOW)
#define slp_set_overflow(h) (h)[SLP_FLAGS] |= SLP_OVERFLOW
#define slp_set_fresh(h) (h)[SLP_FLAGS] |= SLP_FRESH
#define slp_set_mcast(h) (h)[SLP_FLAGS] |= SLP_MCAST