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

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

    // into the range of surrogate characters, but if they do we must not test
    // any values in that range. To see why, consider the case where:
    // safeMin <= {hi,lo} <= safeMax
    // where {hi,lo} are characters forming a surrogate pair such that:
    // codePointOf(hi, lo) > safeMax
    // which would result in the surrogate pair being (wrongly) considered safe.

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

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

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

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

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

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

        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));
          }

    assertStringHash(0xb5a4be05, "ABCDefGHI\u0799", UTF_8);
    assertStringHash(0xfc5ba834, "毎月１日,毎週月曜日", UTF_8);
    assertStringHash(0x8a5c3699, "surrogate pair: \uD83D\uDCB0", UTF_8);

    assertStringHash(0, "", UTF_16LE);
    assertStringHash(0x288418e4, "k", UTF_16LE);
    assertStringHash(0x5a0cb7c3, "hell", UTF_16LE);
    assertStringHash(0xd7c31989, "hello", UTF_16LE);

      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

	}

	// 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))