func ScanRunes(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}

	// Fast path 1: ASCII.
	if data[0] < utf8.RuneSelf {
		return 1, data[0:1], nil
	}

	// Fast path 2: Correct UTF-8 decode without error.
	_, width := utf8.DecodeRune(data)
	if width > 1 {
		// It's a valid encoding. Width cannot be one for a correctly encoded

		n += wasSpace & ^isSpace
		wasSpace = isSpace
	}

	if setBits >= utf8.RuneSelf {
		// Some runes in the input slice are not ASCII.
		return FieldsFunc(s, unicode.IsSpace)
	}

	// ASCII fast path
	a := make([][]byte, n)
	na := 0
	fieldStart := 0
	i := 0
	// Skip spaces in the front of the input.
	for i < len(s) && asciiSpace[s[i]] != 0 {
		i++
	}
	fieldStart = i
	for i < len(s) {

	buf []repeatedByte
}

func (r *rleBuffer) Size() int64 {
	if len(r.buf) == 0 {
		return 0
	}
	last := &r.buf[len(r.buf)-1]
	return last.off + last.n
}

func (r *rleBuffer) Write(p []byte) (n int, err error) {
	var rp *repeatedByte
	if len(r.buf) > 0 {
		rp = &r.buf[len(r.buf)-1]
		// Fast path, if p is entirely the same byte repeated.
		if lastByte := rp.b; len(p) > 0 && p[0] == lastByte {

}

// Use a Scanner with a custom split function to parse a comma-separated
// list with an empty final value.
func ExampleScanner_emptyFinalToken() {
	// Comma-separated list; last entry is empty.
	const input = "1,2,3,4,"
	scanner := bufio.NewScanner(strings.NewReader(input))
	// Define a split function that separates on commas.

		if first != tc.first {
			t.Errorf("IndexFunc(%q, %s) = %d; want %d", tc.in, tc.f.name, first, tc.first)
		}
		last := LastIndexFunc([]byte(tc.in), tc.f.f)
		if last != tc.last {
			t.Errorf("LastIndexFunc(%q, %s) = %d; want %d", tc.in, tc.f.name, last, tc.last)
		}
	}
}

type ReplaceTest struct {
	in       string
	old, new string
	n        int
	out      string
}

	// just ignore these.

	return nil
}

func readDirectoryEnd(r io.ReaderAt, size int64) (dir *directoryEnd, baseOffset int64, err error) {
	// look for directoryEndSignature in the last 1k, then in the last 65k
	var buf []byte
	var directoryEndOffset int64
	for i, bLen := range []int64{1024, 65 * 1024} {
		if bLen > size {
			bLen = size
		}
		buf = make([]byte, int(bLen))

	b.ReportAllocs()
	for i := 0; i < b.N; i++ {
		bb.Reset()
		b := bb.AvailableBuffer()
		b = b[:cap(b)] // use max capacity to simulate a large append operation
		bb.Write(b)    // should be nearly infinitely fast
	}

}

var errUnreadByte = errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read")

// UnreadByte unreads the last byte returned by the most recent successful
// read operation that read at least one byte. If a write has happened since
// the last read, if the last read returned an error, or if the read read zero
// bytes, UnreadByte returns an error.
func (b *Buffer) UnreadByte() error {

//
// If the current file is sparse and r is an io.ReadSeeker,
// then readFrom uses Seek to skip past holes defined in Header.SparseHoles,
// assuming that skipped regions are all NULs.
// This always reads the last byte to ensure r is the right size.
//
// TODO(dsnet): Re-export this when adding sparse file support.
// See https://golang.org/issue/22735

		{"VADDPD.Z.A X0, X1, X2", `Z suffix should be the last; unknown suffix "A"`},
		{"VADDPD.Z.Z X0, X1, X2", `Z suffix should be the last; duplicate suffix "Z"`},
		{"VADDPD.SAE.BCST X0, X1, X2", `can't combine rounding/SAE and broadcast`},
		{"VADDPD.BCST.SAE X0, X1, X2", `can't combine rounding/SAE and broadcast`},
		{"VADDPD.BCST.Z.SAE X0, X1, X2", `Z suffix should be the last; can't combine rounding/SAE and broadcast`},