gistfile1.txt

/* The low-order bit of lock->Ptr is set when the lock is held. If _only_ */
/* the low-order bit is set, the lock is held in exclusive mode. */
BOOLEAN TryAcquireSRWLockExclusive(SRWLOCK* lock) {
  if (sizeof lock->Ptr == sizeof LONG) {
    return InterlockedBitTestAndSet((LONG*) lock->Ptr, 0);
  } else if (sizeof lock->Ptr == sizeof LONG64) {
    return InterlockedBitTestAndSet64((LONG64*) lock->Ptr, 0);
  } else {
    abort();
  }
}