}{
		{call: "Setegid(1)", fn: func() error { return syscall.Setegid(1) }, filter: "Gid:", expect: "\t0\t1\t0\t1"},
		{call: "Setegid(0)", fn: func() error { return syscall.Setegid(0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},

		{call: "Seteuid(1)", fn: func() error { return syscall.Seteuid(1) }, filter: "Uid:", expect: "\t0\t1\t0\t1"},
		{call: "Setuid(0)", fn: func() error { return syscall.Setuid(0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},

			}
			if (x >> 56) > 0 {
				p.err = ErrHeader // Integer overflow
				return 0
			}
			x = x<<8 | uint64(c)
		}
		if (x >> 63) > 0 {
			p.err = ErrHeader // Integer overflow
			return 0
		}
		if inv == 0xff {
			return ^int64(x)
		}
		return int64(x)
	}

	// Normal case is base-8 (octal) format.
	return p.parseOctal(b)
}

	if b == nil {
		// Special case, useful in debugging.
		return "<nil>"
	}
	return string(b.buf[b.off:])
}

// empty reports whether the unread portion of the buffer is empty.
func (b *Buffer) empty() bool { return len(b.buf) <= b.off }

// Len returns the number of bytes of the unread portion of the buffer;
// b.Len() == len(b.Bytes()).
func (b *Buffer) Len() int { return len(b.buf) - b.off }

	}
}

func compressor(method uint16) Compressor {
	ci, ok := compressors.Load(method)
	if !ok {
		return nil
	}
	return ci.(Compressor)
}

func decompressor(method uint16) Decompressor {
	di, ok := decompressors.Load(method)
	if !ok {
		return nil
	}
	return di.(Decompressor)

	case "amd64":
		if goos == "darwin" {
			return []string{"-arch", "x86_64", "-m64"}
		}
		return []string{"-m64"}
	case "arm64":
		if goos == "darwin" {
			return []string{"-arch", "arm64"}
		}
	case "386":
		return []string{"-m32"}
	case "arm":
		return []string{"-marm"} // not thumb
	case "s390":
		return []string{"-m31"}
	case "s390x":
		return []string{"-m64"}
	case "mips64", "mips64le":

	// the BSD tar utility.
	if size < 0 {
		return false
	}
	var pre sparseEntry
	for _, cur := range sp {
		switch {
		case cur.Offset < 0 || cur.Length < 0:
			return false // Negative values are never okay
		case cur.Offset > math.MaxInt64-cur.Length:
			return false // Integer overflow with large length
		case cur.endOffset() > size:
			return false // Region extends beyond the actual size

	if err != nil {
		t.Fatalf("mprotect low failed %s\n", err)
	}
	err = syscall.Mprotect(b[2*pagesize:], syscall.PROT_NONE)
	if err != nil {
		t.Fatalf("mprotect high failed %s\n", err)
	}
	return b[pagesize : 2*pagesize]
}

func TestEqualNearPageBoundary(t *testing.T) {
	t.Parallel()
	b := dangerousSlice(t)
	for i := range b {
		b[i] = 'A'
	}
	for i := 0; i <= len(b); i++ {

	})
}

func writeTestsToFS(tests []WriteTest) fs.FS {
	fsys := fstest.MapFS{}
	for _, wt := range tests {
		fsys[wt.Name] = &fstest.MapFile{
			Data: wt.Data,
			Mode: wt.Mode,
		}
	}
	return fsys
}

func TestWriterAddFS(t *testing.T) {
	buf := new(bytes.Buffer)
	w := NewWriter(buf)
	tests := []WriteTest{
		{
			Name: "file.go",
			Data: []byte("hello"),
			Mode: 0644,
		},

					return 0
				}
			}
			return -1
		}
		if bytealg.IndexByteString(chars, s[0]) >= 0 {
			return 0
		}
		return -1
	}
	if len(chars) == 1 {
		cr := rune(chars[0])
		if cr >= utf8.RuneSelf {
			cr = utf8.RuneError
		}
		for i := len(s); i > 0; {
			r, size := utf8.DecodeLastRune(s[:i])
			i -= size
			if r == cr {
				return i
			}
		}
		return -1
	}

func (tw *Writer) AddFS(fsys fs.FS) error {
	return fs.WalkDir(fsys, ".", func(name string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		info, err := d.Info()
		if err != nil {
			return err
		}
		// TODO(#49580): Handle symlinks when fs.ReadLinkFS is available.
		if !info.Mode().IsRegular() {
			return errors.New("tar: cannot add non-regular file")
		}