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 {

		{"  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")},