FATP_NTAGS
#define FATP_NXT_WIDTH (sizeof(fatp_word_t) * NBBY - FATP_NTAGS)
fatp_word_t inuse : FATP_NTAGS; /* (1+15)*4 == CL_SIZE */
fatp_word_t tag[FATP_NTAGS]; /* 15 tags per CL */
return FATP_NTAGS;
full.inuse = (1U << FATP_NTAGS) - 1U;