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decoder.go
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decoder.go
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package lzma
import "errors"
const (
kNumPosBitsMax = 4
kNumLenToPosStates = 4
kEndPosModelIndex = 14
kNumFullDistances = 1 << (kEndPosModelIndex >> 1)
kNumAlignBits = 4
kNumStates = 12
kMatchMinLen = 2
)
var (
errError = errors.New("decoder internal error")
errNoMarker = errors.New("finished without marker")
errWithMarker = errors.New("finished with marker")
)
type state struct {
isMatch [kNumStates << kNumPosBitsMax]prob
isRep [kNumStates]prob
isRepG0 [kNumStates]prob
isRepG1[kNumStates]prob
isRepG2[kNumStates]prob
isRep0Long[kNumStates << kNumPosBitsMax]prob
lenDecoder lendecoder
repLenDecoder lendecoder
}
type LzmaDecoder struct {
literals
distance
state
props Props
out outWindow
rangeDec rangedecoder
lenDecoder lendecoder
repLenDecoder lendecoder
}
func (ld LzmaDecoder) updateLiteral(state uint) uint {
if state < 4 {
return 0
} else if state < 10 {
return state - 3
} else {
return state - 6
}
}
func (ld LzmaDecoder) updateRep(state uint) uint {
if state < 7 {
return 8
} else {
return 11
}
}
func (ld LzmaDecoder) updateShortRep(state uint) uint {
if state < 7 {
return 9
} else {
return 11
}
}
func (ld LzmaDecoder) updateMatch(state uint) uint {
if state < 7 {
return 7
} else {
return 10
}
}
func NewDecoder(stream []byte) *LzmaDecoder {
decoder := new(LzmaDecoder)
return decoder
}
func (ld *LzmaDecoder) Decode(unpackSize uint64) error {
rep0 := uint(0)
rep1 := uint(0)
rep2 := uint(0)
rep3 := uint(0)
state := uint(0)
for {
if unpackSize == 0 {
if ld.rangeDec.isFinishedOK() {
return errNoMarker
}
}
posState := uint(ld.out.totalPos & ((1 << ld.props.pb) - 1))
db, err := ld.rangeDec.decodeBit(&ld.state.isMatch[(state << kNumPosBitsMax) + posState])
if err != nil {
return err
}
if db == 0 {
if unpackSize == 0 {
return errError
}
if err := ld.decodeLiteral(state, int(rep0)); err != nil {
return err
}
state = ld.updateLiteral(state)
unpackSize--
continue
}
var len uint
db, err = ld.rangeDec.decodeBit(&ld.state.isRep[state])
if err != nil {
return err
}
if db != 0 {
if unpackSize == 0 || ld.out.isEmpty() {
return errError
}
db, err = ld.rangeDec.decodeBit(&ld.state.isRepG0[state])
if err != nil {
return err
}
if db == 0 {
db, err = ld.rangeDec.decodeBit(&ld.state.isRep0Long[(state << kNumPosBitsMax) + posState])
if err != nil {
return err
}
if db == 0 {
state = ld.updateShortRep(state)
ld.out.putByte(ld.out.getByte(int(rep0 + 1)))
unpackSize--
continue
}
} else {
var dist uint
db, err = ld.rangeDec.decodeBit(&ld.state.isRepG1[state])
if err != nil {
return err
}
if db == 0 {
dist = rep1
} else {
db, err = ld.rangeDec.decodeBit(&ld.state.isRepG2[state])
if err != nil {
return err
}
if db == 0 {
dist = rep2
} else {
dist = rep3
rep3 = rep2
}
rep2 = rep1
}
rep1 = rep0
rep0 = dist
}
if len, err = ld.repLenDecoder.decode(&ld.rangeDec, posState) ; err != nil {
return err
}
state = ld.updateRep(state)
} else {
rep3 = rep2
rep2 = rep1
rep1 = rep0
if len, err = ld.lenDecoder.decode(&ld.rangeDec, posState) ; err != nil {
return err
}
state = ld.updateMatch(state)
if rep0, err = ld.decodeDistance(len) ; err != nil {
return err
}
if rep0 == 0xFFFFFFFF {
if ld.rangeDec.isFinishedOK() {
return errWithMarker
} else {
return errError
}
}
if unpackSize == 0 || rep0 >= uint(ld.props.dicSize) || !ld.out.checkDistance(int(rep0)) {
return errError
}
len += kMatchMinLen
if unpackSize < uint64(len) {
return errError
}
if err = ld.out.copyMatch(int(rep0 + 1), len) ; err != nil {
return err
}
unpackSize -= uint64(len)
}
}
}