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)

	"MarshalXML":    {[]string{"*xml.Encoder", "xml.StartElement"}, []string{"error"}}, // xml.Marshaler
	"ReadByte":      {[]string{}, []string{"byte", "error"}},                           // io.ByteReader
	"ReadFrom":      {[]string{"=io.Reader"}, []string{"int64", "error"}},              // io.ReaderFrom
	"ReadRune":      {[]string{}, []string{"rune", "int", "error"}},                    // io.RuneReader

// the [NewReader] will introduce its own buffering.
type Reader interface {
	io.Reader
	io.ByteReader
}

// Decompress state.
type decompressor struct {
	// Input source.
	r       Reader
	rBuf    *bufio.Reader // created if provided io.Reader does not implement io.ByteReader
	roffset int64

	// Input bits, in top of b.
	b  uint32
	nb uint

			// 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 {

// 	if br, ok := r.(io.ByteReader); ok {
// 		return br.ReadByte()
// 	}
// 	var b [1]byte
// 	_, err := r.Read(b[:])
// 	return b[0], err
// }
//
// // ReadBytes2 is like ReadByte1 but uses a type switch instead.
// func ReadByte2[T io.Reader](r T) (byte, error) {
//         switch br := r.(type) {
//         case io.ByteReader:
//                 return br.ReadByte()
//         }

// [fmt.Scan] for floating point values, which are:
// 'b' (binary), 'e', 'E', 'f', 'F', 'g' and 'G'.
// Scan doesn't handle ±Inf.
func (z *Float) Scan(s fmt.ScanState, ch rune) error {
	s.SkipSpace()
	_, _, err := z.scan(byteReader{s}, 0)
	return err

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
}