BPN
(bpb.bpbSecPerClust ? 16 : 12) / BPN,
howmany((RESFTE + maxcls(fat)) * (fat / BPN),
fat / BPN * bpb.bpbFATs);
x2 = howmany((RESFTE + MIN(x, maxcls(fat))) * (fat / BPN),
x = (u_int64_t)bpb.bpbBigFATsecs * bpb.bpbBytesPerSec * NPB / (fat / BPN) -