// * We are more responsive to completion than timeouts. This is because parkNanos depends on
  //   system scheduling and as such we could either miss our deadline, or unpark() could be delayed
  //   so that it looks like we timed out even though we didn't. For comparison FutureTask respects
  //   completion preferably and AQS is non-deterministic (depends on where in the queue the waiter

              if (bitToFlip == index.size()) {
                return endOfData();
              }

              /*
               * The current set in sorted order looks like
               * {firstSetBit, firstSetBit + 1, ..., bitToFlip - 1, ...}
               * where it does *not* contain bitToFlip.
               *
               * The next combination is
               *