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package rardecode
type ppm29Decoder struct {
m model // ppm model
esc byte // escape character
br *rarBitReader
}
func (d *ppm29Decoder) init(br *rarBitReader) error {
maxOrder, err := br.readBits(7)
if err != nil {
return err
}
reset := maxOrder&0x20 > 0
// Move any bytes in rarBitReader bit cache back into a byte slice.
// PPM only reads bytes so it is more efficient to read those bytes
// directly from byte slices, bypassing the extra bit shifts.
br.unshiftBytes()
d.br = br
var maxMB int
if reset {
var c byte
c, err = d.br.ReadByte()
if err != nil {
return err
}
maxMB = int(c) + 1
}
if maxOrder&0x40 > 0 {
d.esc, err = d.br.ReadByte()
if err != nil {
return err
}
}
maxOrder = (maxOrder & 0x1f) + 1
if maxOrder > 16 {
maxOrder = 16 + (maxOrder-16)*3
}
return d.m.init(d.br, reset, maxOrder, maxMB)
}
func (d *ppm29Decoder) reset() {
d.esc = 2
}
func (d *ppm29Decoder) readFilterData() ([]byte, error) {
c, err := d.m.ReadByte()
if err != nil {
return nil, err
}
n := int(c&7) + 1
if n == 7 {
var b byte
b, err = d.m.ReadByte()
if err != nil {
return nil, err
}
n += int(b)
} else if n == 8 {
var b byte
b, err = d.m.ReadByte()
if err != nil {
return nil, err
}
n = int(b) << 8
b, err = d.m.ReadByte()
if err != nil {
return nil, err
}
n |= int(b)
}
n++
buf := make([]byte, n)
buf[0] = c
for i := 1; i < n; i++ {
buf[i], err = d.m.ReadByte()
if err != nil {
return nil, err
}
}
return buf, nil
}
// fill window until full, error, filter found or end of block.
func (d *ppm29Decoder) fill(dr *decodeReader) ([]byte, error) {
for dr.notFull() {
c, err := d.m.ReadByte()
if err != nil {
return nil, err
}
if c != d.esc {
dr.writeByte(c)
continue
}
c, err = d.m.ReadByte()
if err != nil {
return nil, err
}
switch c {
case 0:
return nil, errEndOfBlock
case 2:
return nil, errEndOfBlockAndFile
case 3:
return d.readFilterData()
case 4:
offset := 0
for i := 0; i < 3; i++ {
c, err = d.m.ReadByte()
if err != nil {
return nil, err
}
offset = offset<<8 | int(c)
}
len, err := d.m.ReadByte()
if err != nil {
return nil, err
}
dr.copyBytes(int(len)+32, offset+2)
case 5:
len, err := d.m.ReadByte()
if err != nil {
return nil, err
}
dr.copyBytes(int(len)+4, 1)
default:
dr.writeByte(d.esc)
}
}
return nil, nil
}
func newPPM29Decoder() *ppm29Decoder {
ppm := new(ppm29Decoder)
ppm.reset()
ppm.m.maxOrder = 2
ppm.m.a.init(1)
return ppm
}
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