func TestCastagnoliRace(t *testing.T) {
	// The MakeTable(Castagnoli) lazily initializes castagnoliTable,
	// which races with the switch on tab during Write to check
	// whether tab == castagnoliTable.
	ieee := NewIEEE()
	go MakeTable(Castagnoli)
	ieee.Write([]byte("hello"))
}

type test struct {
	ieee, castagnoli    uint32
	in                  string

	defer timeout(60 * time.Second)()
	const debug = false

	var readBytes int
	var wroteBytes int
	var readBuf bytes.Buffer
	var wroteBuf bytes.Buffer
	readHash := crc32.NewIEEE()
	wroteHash := crc32.NewIEEE()
	read := io.Writer(readHash)
	wrote := io.Writer(wroteHash)
	if debug {
		read = io.MultiWriter(read, &readBuf)
		wrote = io.MultiWriter(wrote, &wroteBuf)
	}

}

// Hasher returns a hasher corresponding to the checksum type.
// Returns nil if no checksum.
func (c ChecksumType) Hasher() hash.Hash {
	switch {
	case c.Is(ChecksumCRC32):
		return crc32.NewIEEE()
	case c.Is(ChecksumCRC32C):
		return crc32.New(crc32.MakeTable(crc32.Castagnoli))
	case c.Is(ChecksumSHA1):
		return sha1.New()
	case c.Is(ChecksumSHA256):
		return sha256.New()
	}
	return nil
}

// Decode reads a PNG image from r and returns it as an [image.Image].
// The type of Image returned depends on the PNG contents.
func Decode(r io.Reader) (image.Image, error) {
	d := &decoder{
		r:   r,
		crc: crc32.NewIEEE(),
	}
	if err := d.checkHeader(); err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		return nil, err
	}
	for d.stage != dsSeenIEND {
		if err := d.parseChunk(false); err != nil {

		return
	}
	binary.BigEndian.PutUint32(e.header[:4], n)
	e.header[4] = name[0]
	e.header[5] = name[1]
	e.header[6] = name[2]
	e.header[7] = name[3]
	crc := crc32.NewIEEE()
	crc.Write(e.header[4:8])
	crc.Write(b)
	binary.BigEndian.PutUint32(e.footer[:4], crc.Sum32())

	_, e.err = e.w.Write(e.header[:8])
	if e.err != nil {
		return
	}
	_, e.err = e.w.Write(b)