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