*   <li>awaits executor service termination for half of the specified timeout.
   *   <li>if the timeout expires, it calls {@link ExecutorService#shutdownNow()}, cancelling
   *       pending tasks and interrupting running tasks.
   *   <li>awaits executor service termination for the other half of the specified timeout.
   * </ol>
   *

      /*
       * The sum of the sums of the hash codes in each subset is just the sum of
       * each input element's hash code times the number of sets that element
       * appears in. Each element appears in exactly half of the 2^n sets, so:
       */
      return inputSet.keySet().hashCode() << (inputSet.size() - 1);
    }

    @Override
    public String toString() {
      return "powerSet(" + inputSet + ")";

    Builder<Integer, String> builder = ImmutableMap.builder();
    Map<Integer, String> expected = new LinkedHashMap<>();
    for (int i = 0; i < 1000; i++) {
      // Truncate to even key, so we have put(0, "0") then put(0, "1"). Half the entries are
      // duplicates.
      Integer key = i & ~1;
      String value = String.valueOf(i);
      builder.put(key, value);
      expected.put(key, value);
    }

     */
    double fractionOfBitsSet = (double) bitCount / bitSize;
    return DoubleMath.roundToLong(
        -Math.log1p(-fractionOfBitsSet) * bitSize / numHashFunctions, RoundingMode.HALF_UP);
  }

  /** Returns the number of bits in the underlying bit array. */
  @VisibleForTesting
  long bitSize() {
    return bits.bitSize();
  }

  /**

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