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126 lines
2.7 KiB
126 lines
2.7 KiB
// Copyright 2014-2021 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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// literalCodec supports the encoding of literal. It provides 768 probability
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// values per literal state. The upper 512 probabilities are used with the
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// context of a match bit.
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type literalCodec struct {
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probs []prob
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}
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// deepcopy initializes literal codec c as a deep copy of the source.
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func (c *literalCodec) deepcopy(src *literalCodec) {
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if c == src {
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return
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}
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c.probs = make([]prob, len(src.probs))
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copy(c.probs, src.probs)
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}
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// init initializes the literal codec.
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func (c *literalCodec) init(lc, lp int) {
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switch {
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case !(minLC <= lc && lc <= maxLC):
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panic("lc out of range")
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case !(minLP <= lp && lp <= maxLP):
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panic("lp out of range")
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}
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c.probs = make([]prob, 0x300<<uint(lc+lp))
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for i := range c.probs {
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c.probs[i] = probInit
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}
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}
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// Encode encodes the byte s using a range encoder as well as the current LZMA
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// encoder state, a match byte and the literal state.
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func (c *literalCodec) Encode(e *rangeEncoder, s byte,
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state uint32, match byte, litState uint32,
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) (err error) {
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k := litState * 0x300
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probs := c.probs[k : k+0x300]
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symbol := uint32(1)
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r := uint32(s)
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if state >= 7 {
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m := uint32(match)
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for {
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matchBit := (m >> 7) & 1
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m <<= 1
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bit := (r >> 7) & 1
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r <<= 1
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i := ((1 + matchBit) << 8) | symbol
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if err = probs[i].Encode(e, bit); err != nil {
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return
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}
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symbol = (symbol << 1) | bit
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if matchBit != bit {
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break
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}
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if symbol >= 0x100 {
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break
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}
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}
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}
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for symbol < 0x100 {
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bit := (r >> 7) & 1
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r <<= 1
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if err = probs[symbol].Encode(e, bit); err != nil {
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return
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}
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symbol = (symbol << 1) | bit
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}
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return nil
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}
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// Decode decodes a literal byte using the range decoder as well as the LZMA
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// state, a match byte, and the literal state.
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func (c *literalCodec) Decode(d *rangeDecoder,
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state uint32, match byte, litState uint32,
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) (s byte, err error) {
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k := litState * 0x300
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probs := c.probs[k : k+0x300]
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symbol := uint32(1)
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if state >= 7 {
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m := uint32(match)
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for {
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matchBit := (m >> 7) & 1
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m <<= 1
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i := ((1 + matchBit) << 8) | symbol
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bit, err := d.DecodeBit(&probs[i])
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if err != nil {
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return 0, err
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}
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symbol = (symbol << 1) | bit
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if matchBit != bit {
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break
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}
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if symbol >= 0x100 {
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break
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}
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}
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}
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for symbol < 0x100 {
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bit, err := d.DecodeBit(&probs[symbol])
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if err != nil {
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return 0, err
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}
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symbol = (symbol << 1) | bit
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}
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s = byte(symbol - 0x100)
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return s, nil
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}
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// minLC and maxLC define the range for LC values.
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const (
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minLC = 0
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maxLC = 8
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)
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// minLC and maxLC define the range for LP values.
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const (
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minLP = 0
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maxLP = 4
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)
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