269 lines
6.6 KiB
Go
269 lines
6.6 KiB
Go
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// Copyright 2014-2017 Ulrich Kunitz. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package lzma
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import (
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"fmt"
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"io"
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)
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// opLenMargin provides the upper limit of the number of bytes required
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// to encode a single operation.
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const opLenMargin = 10
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// compressFlags control the compression process.
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type compressFlags uint32
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// Values for compressFlags.
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const (
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// all data should be compressed, even if compression is not
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// optimal.
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all compressFlags = 1 << iota
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)
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// encoderFlags provide the flags for an encoder.
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type encoderFlags uint32
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// Flags for the encoder.
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const (
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// eosMarker requests an EOS marker to be written.
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eosMarker encoderFlags = 1 << iota
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)
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// Encoder compresses data buffered in the encoder dictionary and writes
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// it into a byte writer.
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type encoder struct {
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dict *encoderDict
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state *state
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re *rangeEncoder
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start int64
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// generate eos marker
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marker bool
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limit bool
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margin int
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}
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// newEncoder creates a new encoder. If the byte writer must be
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// limited use LimitedByteWriter provided by this package. The flags
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// argument supports the eosMarker flag, controlling whether a
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// terminating end-of-stream marker must be written.
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func newEncoder(bw io.ByteWriter, state *state, dict *encoderDict,
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flags encoderFlags) (e *encoder, err error) {
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re, err := newRangeEncoder(bw)
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if err != nil {
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return nil, err
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}
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e = &encoder{
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dict: dict,
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state: state,
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re: re,
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marker: flags&eosMarker != 0,
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start: dict.Pos(),
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margin: opLenMargin,
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}
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if e.marker {
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e.margin += 5
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}
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return e, nil
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}
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// Write writes the bytes from p into the dictionary. If not enough
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// space is available the data in the dictionary buffer will be
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// compressed to make additional space available. If the limit of the
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// underlying writer has been reached ErrLimit will be returned.
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func (e *encoder) Write(p []byte) (n int, err error) {
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for {
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k, err := e.dict.Write(p[n:])
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n += k
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if err == ErrNoSpace {
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if err = e.compress(0); err != nil {
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return n, err
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}
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continue
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}
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return n, err
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}
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}
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// Reopen reopens the encoder with a new byte writer.
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func (e *encoder) Reopen(bw io.ByteWriter) error {
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var err error
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if e.re, err = newRangeEncoder(bw); err != nil {
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return err
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}
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e.start = e.dict.Pos()
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e.limit = false
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return nil
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}
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// writeLiteral writes a literal into the LZMA stream
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func (e *encoder) writeLiteral(l lit) error {
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var err error
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state, state2, _ := e.state.states(e.dict.Pos())
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if err = e.state.isMatch[state2].Encode(e.re, 0); err != nil {
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return err
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}
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litState := e.state.litState(e.dict.ByteAt(1), e.dict.Pos())
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match := e.dict.ByteAt(int(e.state.rep[0]) + 1)
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err = e.state.litCodec.Encode(e.re, l.b, state, match, litState)
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if err != nil {
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return err
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}
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e.state.updateStateLiteral()
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return nil
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}
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// iverson implements the Iverson operator as proposed by Donald Knuth in his
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// book Concrete Mathematics.
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func iverson(ok bool) uint32 {
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if ok {
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return 1
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}
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return 0
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}
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// writeMatch writes a repetition operation into the operation stream
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func (e *encoder) writeMatch(m match) error {
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var err error
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if !(minDistance <= m.distance && m.distance <= maxDistance) {
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panic(fmt.Errorf("match distance %d out of range", m.distance))
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}
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dist := uint32(m.distance - minDistance)
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if !(minMatchLen <= m.n && m.n <= maxMatchLen) &&
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!(dist == e.state.rep[0] && m.n == 1) {
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panic(fmt.Errorf(
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"match length %d out of range; dist %d rep[0] %d",
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m.n, dist, e.state.rep[0]))
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}
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state, state2, posState := e.state.states(e.dict.Pos())
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if err = e.state.isMatch[state2].Encode(e.re, 1); err != nil {
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return err
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}
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g := 0
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for ; g < 4; g++ {
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if e.state.rep[g] == dist {
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break
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}
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}
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b := iverson(g < 4)
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if err = e.state.isRep[state].Encode(e.re, b); err != nil {
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return err
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}
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n := uint32(m.n - minMatchLen)
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if b == 0 {
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// simple match
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e.state.rep[3], e.state.rep[2], e.state.rep[1], e.state.rep[0] =
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e.state.rep[2], e.state.rep[1], e.state.rep[0], dist
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e.state.updateStateMatch()
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if err = e.state.lenCodec.Encode(e.re, n, posState); err != nil {
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return err
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}
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return e.state.distCodec.Encode(e.re, dist, n)
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}
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b = iverson(g != 0)
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if err = e.state.isRepG0[state].Encode(e.re, b); err != nil {
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return err
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}
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if b == 0 {
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// g == 0
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b = iverson(m.n != 1)
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if err = e.state.isRepG0Long[state2].Encode(e.re, b); err != nil {
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return err
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}
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if b == 0 {
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e.state.updateStateShortRep()
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return nil
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}
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} else {
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// g in {1,2,3}
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b = iverson(g != 1)
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if err = e.state.isRepG1[state].Encode(e.re, b); err != nil {
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return err
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}
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if b == 1 {
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// g in {2,3}
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b = iverson(g != 2)
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err = e.state.isRepG2[state].Encode(e.re, b)
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if err != nil {
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return err
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}
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if b == 1 {
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e.state.rep[3] = e.state.rep[2]
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}
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e.state.rep[2] = e.state.rep[1]
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}
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e.state.rep[1] = e.state.rep[0]
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e.state.rep[0] = dist
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}
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e.state.updateStateRep()
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return e.state.repLenCodec.Encode(e.re, n, posState)
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}
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// writeOp writes a single operation to the range encoder. The function
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// checks whether there is enough space available to close the LZMA
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// stream.
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func (e *encoder) writeOp(op operation) error {
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if e.re.Available() < int64(e.margin) {
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return ErrLimit
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}
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switch x := op.(type) {
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case lit:
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return e.writeLiteral(x)
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case match:
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return e.writeMatch(x)
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default:
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panic("unexpected operation")
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}
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}
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// compress compressed data from the dictionary buffer. If the flag all
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// is set, all data in the dictionary buffer will be compressed. The
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// function returns ErrLimit if the underlying writer has reached its
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// limit.
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func (e *encoder) compress(flags compressFlags) error {
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n := 0
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if flags&all == 0 {
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n = maxMatchLen - 1
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}
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d := e.dict
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m := d.m
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for d.Buffered() > n {
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op := m.NextOp(e.state.rep)
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if err := e.writeOp(op); err != nil {
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return err
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}
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d.Discard(op.Len())
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}
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return nil
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}
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// eosMatch is a pseudo operation that indicates the end of the stream.
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var eosMatch = match{distance: maxDistance, n: minMatchLen}
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// Close terminates the LZMA stream. If requested the end-of-stream
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// marker will be written. If the byte writer limit has been or will be
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// reached during compression of the remaining data in the buffer the
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// LZMA stream will be closed and data will remain in the buffer.
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func (e *encoder) Close() error {
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err := e.compress(all)
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if err != nil && err != ErrLimit {
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return err
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}
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if e.marker {
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if err := e.writeMatch(eosMatch); err != nil {
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return err
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}
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}
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err = e.re.Close()
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return err
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}
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// Compressed returns the number bytes of the input data that been
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// compressed.
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func (e *encoder) Compressed() int64 {
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return e.dict.Pos() - e.start
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}
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