}

	// check for proceeding surrogate pair
	c = d.next()
	if !utf16.IsSurrogate(r) || c != '\\' {
		d.scratch.addRune(r)
		goto scan
	}
	if c = d.next(); c != 'u' {
		d.scratch.addRune(r)
		goto scan_esc
	}

	r2 := d.u4()
	if r2 < 0 {
		return "", d.mkError(ErrSyntax, "in unicode escape sequence")
	}

	// write surrogate pair
	d.scratch.addRune(utf16.DecodeRune(r, r2))

      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

        utf8Length += (0x7f - c) >>> 31; // branch free!
      } else {
        utf8Length += 2;
        // We can't use Character.isSurrogate(c) here and below because of GWT.
        if (MIN_SURROGATE <= c && c <= MAX_SURROGATE) {
          // Check that we have a well-formed surrogate pair.
          if (Character.codePointAt(sequence, i) == c) {
            throw new IllegalArgumentException(unpairedSurrogateMsg(i));
          }

        utf8Length += (0x7f - c) >>> 31; // branch free!
      } else {
        utf8Length += 2;
        // We can't use Character.isSurrogate(c) here and below because of GWT.
        if (MIN_SURROGATE <= c && c <= MAX_SURROGATE) {
          // Check that we have a well-formed surrogate pair.
          if (Character.codePointAt(sequence, i) == c) {
            throw new IllegalArgumentException(unpairedSurrogateMsg(i));
          }

      MAX_LOW_SURROGATE, MAX_HIGH_SURROGATE, MIN_LOW_SURROGATE, MIN_HIGH_SURROGATE,
    };
    for (char surrogate : surrogates) {
      builder.add(newString(surrogate));
      builder.add(newString(surrogate, 'n'));
      builder.add(newString('n', surrogate));
      builder.add(newString(surrogate, surrogate));
    }
    builder.add(newString(MIN_LOW_SURROGATE, MAX_HIGH_SURROGATE));
    ILL_FORMED_STRINGS = builder.build();
  }

    pos: Int,
    limit: Int,
  ): List<Int> {
    val result = mutableListOf<Int>()
    var i = pos
    while (i < limit) {
      val c = this[i]
      result +=
        when {
          c.isSurrogate() -> {
            val low = (if (i + 1 < limit) this[i + 1] else '\u0000')
            if (c.isLowSurrogate() || !low.isLowSurrogate()) {
              '?'.code
            } else {
              i++

   *             surrogate is returned.</b>
   *         <li><b>If the next character was a valid low surrogate, the code point value of the
   *             high/low surrogate pair is returned.</b>
   *         <li>If the next character was not a low surrogate value, then {@link
   *             IllegalArgumentException} is thrown.
   *       </ol>

    assertThat(Strings.commonPrefix(new StringBuilder("abcdef"), "abcxyz")).isEqualTo("abc");

    // Identical valid surrogate pairs.
    assertThat(Strings.commonPrefix("abc\uD8AB\uDCABdef", "abc\uD8AB\uDCABxyz"))
        .isEqualTo("abc\uD8AB\uDCAB");
    // Differing valid surrogate pairs.
    assertThat(Strings.commonPrefix("abc\uD8AB\uDCABdef", "abc\uD8AB\uDCACxyz")).isEqualTo("abc");
    // One invalid pair.

    // Build up a range of surrogate pair characters to test
    int min = Character.MIN_SUPPLEMENTARY_CODE_POINT;
    int max = Character.MAX_CODE_POINT;
    int range = max - min;
    int s1 = min + (1 * range) / 4;
    int s2 = min + (2 * range) / 4;
    int s3 = min + (3 * range) / 4;
    char[] dst = new char[12];

    // Put surrogate pairs at odd indices so they can be split easily

    assertThat(Strings.commonPrefix(new StringBuilder("abcdef"), "abcxyz")).isEqualTo("abc");

    // Identical valid surrogate pairs.
    assertThat(Strings.commonPrefix("abc\uD8AB\uDCABdef", "abc\uD8AB\uDCABxyz"))
        .isEqualTo("abc\uD8AB\uDCAB");
    // Differing valid surrogate pairs.
    assertThat(Strings.commonPrefix("abc\uD8AB\uDCABdef", "abc\uD8AB\uDCACxyz")).isEqualTo("abc");
    // One invalid pair.