if r >= utf8.RuneSelf {
			// search utf8.RuneError.
			for _, r = range chars {
				if r == utf8.RuneError {
					return 0
				}
			}
			return -1
		}
		if bytealg.IndexByteString(chars, s[0]) >= 0 {
			return 0
		}
		return -1
	}
	if len(chars) == 1 {
		r := rune(chars[0])
		if r >= utf8.RuneSelf {
			r = utf8.RuneError
		}
		return IndexRune(s, r)
	}
	if len(s) > 8 {

		//
		// Forbid 0x7e and 0x5c since EUC-KR and Shift-JIS replace those
		// characters with localized currency and overline characters.
		if r < 0x20 || r > 0x7d || r == 0x5c {
			if !utf8.ValidRune(r) || (r == utf8.RuneError && size == 1) {
				return false, false
			}
			require = true
		}
	}
	return true, require
}

// prepare performs the bookkeeping operations required at the start of

		}
	}
}

func TestWriteInvalidRune(t *testing.T) {
	// Invalid runes, including negative ones, should be written as
	// utf8.RuneError.
	for _, r := range []rune{-1, utf8.MaxRune + 1} {
		var buf Buffer
		buf.WriteRune(r)
		check(t, fmt.Sprintf("TestWriteInvalidRune (%d)", r), &buf, "\uFFFD")
	}
}

func TestNext(t *testing.T) {

		{"  𡌀", '𡌀', 2},
		{"  a", '𡌀', -1},
		{strings.Repeat("𡋀", 64) + "𡌀", '𡌀', 256}, // test cutover
		{strings.Repeat("𡋀", 64) + "𡌀", '𣌀', -1},  // '𡌀' and '𣌀' share the same last two bytes

		// RuneError should match any invalid UTF-8 byte sequence.
		{"�", '�', 0},
		{"\xff", '�', 0},
		{"☻x�", '�', len("☻x")},
		{"☻x\xe2\x98", '�', len("☻x")},
		{"☻x\xe2\x98�", '�', len("☻x")},
		{"☻x\xe2\x98x", '�', len("☻x")},

		return p.atoi(tok.String())
	case scanner.Char:
		str, err := strconv.Unquote(tok.String())
		if err != nil {
			p.errorf("%s", err)
		}
		r, w := utf8.DecodeRuneInString(str)
		if w == 1 && r == utf8.RuneError {
			p.errorf("illegal UTF-8 encoding for character constant")
		}
		return uint64(r)
	case '+':
		return +p.factor()
	case '-':
		return -p.factor()
	case '~':
		return ^p.factor()