}
	buf := make([]byte, ss.Size())
	for off := int64(0); off < ss.Size(); off++ {
		for size := 1; size <= int(ss.Size()-off); size++ {
			readBuf := buf[:size]
			n, err := ss.ReadAt(readBuf, off)
			if off < ss.Size()-keep {
				if err != errDiscardedBytes {
					t.Errorf("off %d, size %d = %v, %v (%q); want errDiscardedBytes", off, size, n, err, readBuf[:n])
				}
				continue
			}

	r := NewReader([]byte("0123456789"))
	tests := []struct {
		off     int64
		seek    int
		n       int
		want    string
		wantpos int64
		readerr error
		seekerr string
	}{
		{seek: io.SeekStart, off: 0, n: 20, want: "0123456789"},
		{seek: io.SeekStart, off: 1, n: 1, want: "1"},
		{seek: io.SeekCurrent, off: 1, wantpos: 3, n: 2, want: "34"},
		{seek: io.SeekStart, off: -1, seekerr: "bytes.Reader.Seek: negative position"},

	return
}

// ReadAt implements the [io.ReaderAt] interface.
func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
	// cannot modify state - see io.ReaderAt
	if off < 0 {
		return 0, errors.New("bytes.Reader.ReadAt: negative offset")
	}
	if off >= int64(len(r.s)) {
		return 0, io.EOF
	}
	n = copy(b, r.s[off:])
	if n < len(b) {
		err = io.EOF
	}
	return
}

// TrimLeftFunc treats s as UTF-8-encoded bytes and returns a subslice of s by slicing off
// all leading UTF-8-encoded code points c that satisfy f(c).
func TrimLeftFunc(s []byte, f func(r rune) bool) []byte {
	i := indexFunc(s, f, false)
	if i == -1 {
		return nil
	}
	return s[i:]
}

// TrimRightFunc returns a subslice of s by slicing off all trailing
// UTF-8-encoded code points c that satisfy f(c).

			}
			count = int16((x & 31) << 7)
		}
	default:
		p.errorf("unexpected %s in register shift", tok.String())
	}
	if p.arch.Family == sys.ARM64 {
		off, err := arch.ARM64RegisterShift(r1, op, count)
		if err != nil {
			p.errorf(err.Error())
		}
		return off
	} else {
		return int64((r1 & 15) | op<<5 | count)
	}
}

// registerExtension parses a register with extension or arrangement.

pkg syscall (darwin-386), const IP_RETOPTS = 8
pkg syscall (darwin-386), const IP_RF = 32768
pkg syscall (darwin-386), const IP_RSVP_OFF = 16
pkg syscall (darwin-386), const IP_RSVP_ON = 15
pkg syscall (darwin-386), const IP_RSVP_VIF_OFF = 18
pkg syscall (darwin-386), const IP_RSVP_VIF_ON = 17
pkg syscall (darwin-386), const IP_STRIPHDR = 23
pkg syscall (darwin-386), const IP_TOS = 3

	{
		"LOAD macro",
		lines(
			"#define LOAD(off, reg) \\",
			"\tMOVBLZX	(off*4)(R12),	reg \\",
			"\tADDB	reg,		DX",
			"",
			"LOAD(8, AX)",
		),
		"\n.\n.MOVBLZX.(.8.*.4.).(.R12.).,.AX.\n.ADDB.AX.,.DX.\n",
	},
	{
		"nested multiline macro",
		lines(
			"#define KEYROUND(xmm, load, off, r1, r2, index) \\",
			"\tMOVBLZX	(BP)(DX*4),	R8 \\",
			"\tload((off+1), r2) \\",
			"\tMOVB	R8,		(off*4)(R12) \\",

	if _, err := io.ReadFull(r, buf[:4]); err != nil {
		return err
	}
	off := 0
	maybeSig := readBuf(buf[:4])
	if maybeSig.uint32() != dataDescriptorSignature {
		// No data descriptor signature. Keep these four
		// bytes.
		off += 4
	}
	if _, err := io.ReadFull(r, buf[off:12]); err != nil {
		return err
	}
	b := readBuf(buf[:12])
	if b.uint32() != f.CRC32 {

	if res.StatusCode/100 == 3 {
		newURL, err := res.Location()
		if err != nil {
			return fmt.Errorf("resolving redirect: %v", err)
		}
		if !strings.HasPrefix(newURL.String(), *root) {
			// Skip off-site redirects.
			return nil
		}
		crawl(newURL.String(), url)
		return nil
	}
	if res.StatusCode != 200 {
		return errors.New(res.Status)
	}
	slurp, err := io.ReadAll(res.Body)
	res.Body.Close()

	if len(bmbuf) < maxSize {
		bmbuf = make([]byte, maxSize)
	}

	for _, n := range sizes {
		for _, off := range []int{0, 1, 4, 7} {
			buf1 := bmbuf[off : off+n]
			buf2Start := (len(bmbuf) / 2) + off
			buf2 := bmbuf[buf2Start : buf2Start+n]
			buf1[n-1] = 'x'
			buf2[n-1] = 'x'
			b.Run(fmt.Sprint(n, off), func(b *testing.B) {
				b.SetBytes(int64(n))
				for i := 0; i < b.N; i++ {
					eq := Equal(buf1, buf2)