return b.exp == event.NoExperiment && len(b.data) > 0 && event.Type(b.data[0]) == go122.EvFrequency
}

// readBatch reads the next full batch from r.
func readBatch(r interface {
	io.Reader
	io.ByteReader
}) (batch, uint64, error) {
	// Read batch header byte.
	b, err := r.ReadByte()
	if err != nil {
		return batch{}, 0, err
	}
	if typ := event.Type(b); typ != go122.EvEventBatch && typ != go122.EvExperimentalBatch {

	errBadPixel  = errors.New("gif: invalid pixel value")
)

// If the io.Reader does not also have ReadByte, then decode will introduce its own buffering.
type reader interface {
	io.Reader
	io.ByteReader
}

// Masks etc.
const (
	// Fields.
	fColorTable         = 1 << 7
	fInterlace          = 1 << 6
	fColorTableBitsMask = 7

	// Graphic control flags.
	gcTransparentColorSet = 1 << 0

var ErrLineTooLong = internal.ErrLineTooLong

type errorReader struct {
	err error
}

func (r errorReader) Read(p []byte) (n int, err error) {
	return 0, r.err
}

type byteReader struct {
	b    byte
	done bool
}

func (br *byteReader) Read(p []byte) (n int, err error) {
	if br.done {
		return 0, io.EOF
	}
	if len(p) == 0 {
		return 0, nil
	}
	br.done = true
	p[0] = br.b
	return 1, io.EOF
}

//
// ReadByte provides an efficient interface for byte-at-time
// processing. A [Reader] that does not implement  ByteReader
// can be wrapped using bufio.NewReader to add this method.
type ByteReader interface {
	ReadByte() (byte, error)
}

// ByteScanner is the interface that adds the UnreadByte method to the
// basic ReadByte method.
//
// UnreadByte causes the next call to ReadByte to return the last byte read.

	paletteStr = "\x10\x20\x30\x40\x50\x60" // the color table, also known as a palette
	trailerStr = "\x3b"
)

// lzw.NewReader wants an io.ByteReader, this ensures we're compatible.
var _ io.ByteReader = (*blockReader)(nil)

// lzwEncode returns an LZW encoding (with 2-bit literals) of in.
func lzwEncode(in []byte) []byte {
	b := &bytes.Buffer{}
	w := lzw.NewWriter(b, lzw.LSB, 2)

			// Get next bit - fast path.
			br.bits--
			bit = uint16(br.n>>(br.bits&63)) & 1
		} else {
			// Get next bit - slow path.
			// Use ReadBits to retrieve a single bit
			// from the underling io.ByteReader.
			bit = uint16(br.ReadBits(1))
		}

		// Trick a compiler into generating conditional move instead of branch,
		// by making both loads unconditional.
		l, r := node.left, node.right

		if bit == 1 {

func (r *Reader) Read(p []byte) (int, error) {
	if err := r.refillIfNeeded(); err != nil {
		return 0, err
	}
	n := copy(p, r.buffer[r.off:])
	r.off += n
	return n, nil
}

// ReadByte implements [io.ByteReader].
func (r *Reader) ReadByte() (byte, error) {
	if err := r.refillIfNeeded(); err != nil {
		return 0, err
	}
	ret := r.buffer[r.off]
	r.off++
	return ret, nil
}

	repeats     uint     // the number of copies of lastByte to output.
}

// NewReader returns an io.Reader which decompresses bzip2 data from r.
// If r does not also implement [io.ByteReader],
// the decompressor may read more data than necessary from r.
func NewReader(r io.Reader) io.Reader {
	bz2 := new(reader)
	bz2.br = newBitReader(r)
	return bz2
}

const bzip2FileMagic = 0x425a // "BZ"

	// as if the entire XML stream were wrapped in an element containing
	// the attribute xmlns="DefaultSpace".
	DefaultSpace string

	r              io.ByteReader
	t              TokenReader
	buf            bytes.Buffer
	saved          *bytes.Buffer
	stk            *stack
	free           *stack
	needClose      bool
	toClose        Name
	nextToken      Token

	d := NewDecoder(strings.NewReader(nonStrictInput))
	d.Strict = false
	testRawToken(t, d, nonStrictInput, nonStrictTokens)
}

type downCaser struct {
	t *testing.T
	r io.ByteReader
}

func (d *downCaser) ReadByte() (c byte, err error) {
	c, err = d.r.ReadByte()
	if c >= 'A' && c <= 'Z' {
		c += 'a' - 'A'
	}
	return
}

func (d *downCaser) Read(p []byte) (int, error) {