for (int z = 0; z < 100; z++) {
      int[] codePoints = new int[rng.nextInt(8)];
      for (int i = 0; i < codePoints.length; i++) {
        do {
          codePoints[i] = rng.nextInt(0x800);
        } while (!Character.isValidCodePoint(codePoints[i])
            || (codePoints[i] >= Character.MIN_SURROGATE
                && codePoints[i] <= Character.MAX_SURROGATE));
      }

      StringBuilder sb = new StringBuilder();
      for (int j = 0; j < charCount; j++) {
        int codePoint;
        // discard illegal surrogate "codepoints"
        do {
          codePoint = rnd.nextInt(maxCodePoint.value);
        } while (Character.isSurrogate((char) codePoint));
        sb.appendCodePoint(codePoint);
      }
      strings[i] = sb.toString();
    }
  }

  @Benchmark

      StringBuilder sb = new StringBuilder();
      for (int j = 0; j < charCount; j++) {
        int codePoint;
        // discard illegal surrogate "codepoints"
        do {
          codePoint = rnd.nextInt(maxCodePoint.value);
        } while (Character.isSurrogate((char) codePoint));
        sb.appendCodePoint(codePoint);
      }
      strings[i] = sb.toString();
    }
  }

  @Benchmark

        if (byte2 > (byte) 0xBF
            // Overlong? 5 most significant bits must not all be zero.
            || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
            // Check for illegal surrogate codepoints.
            || (byte1 == (byte) 0xED && (byte) 0xA0 <= byte2)
            // Third byte trailing-byte test.
            || bytes[index++] > (byte) 0xBF) {
          return false;
        }
      } else {

  private static long codePointToFourUtf8Bytes(int codePoint) {
    // codePoint has at most 21 bits
    return ((0xFL << 4) | (codePoint >>> 18))
        | ((0x80L | (0x3F & (codePoint >>> 12))) << 8)
        | ((0x80L | (0x3F & (codePoint >>> 6))) << 16)
        | ((0x80L | (0x3F & codePoint)) << 24);
  }

  private static long charToThreeUtf8Bytes(char c) {
    return ((0x7L << 5) | (c >>> 12))