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// 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
)
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