private static final int BYTE_MASK = (1 << Byte.SIZE) - 1; // 2^8 - 1 = 255
  private static final int SHORT_MASK = (1 << Short.SIZE) - 1; // 2^16 - 1 = 65_535

  @SuppressWarnings("unchecked")
  static final ImmutableMap<Object, Object> EMPTY =
      new RegularImmutableMap<>(null, new Object[0], 0);

  /*

  private static final int BYTE_MASK = (1 << Byte.SIZE) - 1; // 2^8 - 1 = 255

  private static final int SHORT_MAX_SIZE = 1 << Short.SIZE; // 2^16 = 65_536
  private static final int SHORT_MASK = (1 << Short.SIZE) - 1; // 2^16 - 1 = 65_535

  /**
   * Returns the power of 2 hashtable size required to hold the expected number of items or the
   * minimum hashtable size, whichever is greater.
   */

  private static final int BYTE_MASK = (1 << Byte.SIZE) - 1; // 2^8 - 1 = 255

  private static final int SHORT_MAX_SIZE = 1 << Short.SIZE; // 2^16 = 65_536
  private static final int SHORT_MASK = (1 << Short.SIZE) - 1; // 2^16 - 1 = 65_535

  /**
   * Returns the power of 2 hashtable size required to hold the expected number of items or the
   * minimum hashtable size, whichever is greater.
   */

  /*
   * Arrays are a mess from a nullness perspective, and Class instances for object-array types are
   * even worse. For now, we just suppress and move on with our lives.
   *
   * - https://github.com/jspecify/jspecify/issues/65
   *
   * - https://github.com/jspecify/jdk/commit/71d826792b8c7ef95d492c50a274deab938f2552
   */
  /*
   * TODO(cpovirk): Is the unchecked cast avoidable? Would System.arraycopy be similarly fast (if

    bigValues.add(BigInteger.valueOf(Long.MAX_VALUE).add(ONE));
    // Now add values near 2^N for lots of values of N.
    for (int exponent :
        asList(
            64,
            65,
            71,
            72,
            73,
            79,
            80,
            81,
            255,
            256,
            257,
            511,
            512,

    bigValues.add(BigInteger.valueOf(Long.MAX_VALUE).add(ONE));
    // Now add values near 2^N for lots of values of N.
    for (int exponent :
        asList(
            64,
            65,
            71,
            72,
            73,
            79,
            80,
            81,
            255,
            256,
            257,
            511,
            512,