SYNCOOKIE_WNDBITS
#define SYNCOOKIE_WNDMASK ((1 << SYNCOOKIE_WNDBITS) - 1)
#define SYNCOOKIE_NSECRETS (1 << SYNCOOKIE_WNDBITS)
(hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT))
#define SYNCOOKIE_DATAMASK ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK)
data = (data << SYNCOOKIE_WNDBITS) | idx;
data = data >> SYNCOOKIE_WNDBITS;