mirror of
https://github.com/aptly-dev/aptly.git
synced 2026-04-20 19:38:39 +00:00
129 lines
3.0 KiB
Go
129 lines
3.0 KiB
Go
// Copyright (c) 2010, Andrei Vieru. 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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type litSubCoder struct {
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coders []uint16
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}
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func newLitSubCoder() *litSubCoder {
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return &litSubCoder{
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coders: initBitModels(0x300),
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}
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}
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func (lsc *litSubCoder) decodeNormal(rd *rangeDecoder) byte {
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symbol := uint32(1)
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for symbol < 0x100 {
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i := rd.decodeBit(lsc.coders, symbol)
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symbol = symbol<<1 | i
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}
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return byte(symbol)
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}
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func (lsc *litSubCoder) decodeWithMatchByte(rd *rangeDecoder, matchByte byte) byte {
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uMatchByte := uint32(matchByte)
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symbol := uint32(1)
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for symbol < 0x100 {
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matchBit := (uMatchByte >> 7) & 1
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uMatchByte <<= 1
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bit := rd.decodeBit(lsc.coders, ((1+matchBit)<<8)+symbol)
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symbol = (symbol << 1) | bit
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if matchBit != bit {
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for symbol < 0x100 {
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i := rd.decodeBit(lsc.coders, symbol)
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symbol = (symbol << 1) | i
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}
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break
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}
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}
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return byte(symbol)
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}
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func (lsc *litSubCoder) encode(re *rangeEncoder, symbol byte) {
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uSymbol := uint32(symbol)
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context := uint32(1)
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for i := uint32(7); int32(i) >= 0; i-- {
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bit := (uSymbol >> i) & 1
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re.encode(lsc.coders, context, bit)
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context = context<<1 | bit
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}
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}
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func (lsc *litSubCoder) encodeMatched(re *rangeEncoder, matchByte, symbol byte) {
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uMatchByte := uint32(matchByte)
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uSymbol := uint32(symbol)
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context := uint32(1)
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same := true
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for i := uint32(7); int32(i) >= 0; i-- {
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bit := (uSymbol >> i) & 1
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state := context
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if same == true {
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matchBit := (uMatchByte >> i) & 1
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state += (1 + matchBit) << 8
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same = false
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if matchBit == bit {
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same = true
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}
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}
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re.encode(lsc.coders, state, bit)
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context = context<<1 | bit
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}
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}
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func (lsc *litSubCoder) getPrice(matchMode bool, matchByte, symbol byte) uint32 {
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uMatchByte := uint32(matchByte)
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uSymbol := uint32(symbol)
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price := uint32(0)
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context := uint32(1)
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i := uint32(7)
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if matchMode == true {
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for ; int32(i) >= 0; i-- {
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matchBit := (uMatchByte >> i) & 1
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bit := (uSymbol >> i) & 1
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price += getPrice(lsc.coders[(1+matchBit)<<8+context], bit)
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context = context<<1 | bit
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if matchBit != bit {
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i--
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break
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}
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}
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}
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for ; int32(i) >= 0; i-- {
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bit := (uSymbol >> i) & 1
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price += getPrice(lsc.coders[context], bit)
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context = context<<1 | bit
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}
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return price
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}
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type litCoder struct {
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coders []*litSubCoder
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numPrevBits uint32 // literal context bits // lc
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// numPosBits uint32 // literal position state bits // lp
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posMask uint32
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}
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func newLitCoder(numPosBits, numPrevBits uint32) *litCoder {
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numStates := uint32(1) << (numPrevBits + numPosBits)
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lc := &litCoder{
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coders: make([]*litSubCoder, numStates),
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numPrevBits: numPrevBits,
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// numPosBits: numPosBits,
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posMask: (1 << numPosBits) - 1,
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}
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for i := uint32(0); i < numStates; i++ {
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lc.coders[i] = newLitSubCoder()
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}
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return lc
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}
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func (lc *litCoder) getSubCoder(pos uint32, prevByte byte) *litSubCoder {
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return lc.coders[((pos&lc.posMask)<<lc.numPrevBits)+uint32(prevByte>>(8-lc.numPrevBits))]
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}
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