jochen
10f76cafc4
Betterbird's pinned .tar.xz failed on the build seat with "this build seat has no xz to read it": the seat's image is the catalogue's build-agent recipe, which installs git and docker-cli alone, and xz had been added only to cmd/mesh-builder/Dockerfile, which the seat does not build from. The stream is now read with github.com/ulikunitz/xz (vendored), its dictionary capped at xz's own largest preset, and what it unpacks to bounded as before; the xz line in the unused Dockerfile is taken back out.
116 lines
2.7 KiB
Go
116 lines
2.7 KiB
Go
// Copyright 2014-2022 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
|
|
|
|
import "errors"
|
|
|
|
// maxPosBits defines the number of bits of the position value that are used to
|
|
// to compute the posState value. The value is used to select the tree codec
|
|
// for length encoding and decoding.
|
|
const maxPosBits = 4
|
|
|
|
// minMatchLen and maxMatchLen give the minimum and maximum values for
|
|
// encoding and decoding length values. minMatchLen is also used as base
|
|
// for the encoded length values.
|
|
const (
|
|
minMatchLen = 2
|
|
maxMatchLen = minMatchLen + 16 + 256 - 1
|
|
)
|
|
|
|
// lengthCodec support the encoding of the length value.
|
|
type lengthCodec struct {
|
|
choice [2]prob
|
|
low [1 << maxPosBits]treeCodec
|
|
mid [1 << maxPosBits]treeCodec
|
|
high treeCodec
|
|
}
|
|
|
|
// deepcopy initializes the lc value as deep copy of the source value.
|
|
func (lc *lengthCodec) deepcopy(src *lengthCodec) {
|
|
if lc == src {
|
|
return
|
|
}
|
|
lc.choice = src.choice
|
|
for i := range lc.low {
|
|
lc.low[i].deepcopy(&src.low[i])
|
|
}
|
|
for i := range lc.mid {
|
|
lc.mid[i].deepcopy(&src.mid[i])
|
|
}
|
|
lc.high.deepcopy(&src.high)
|
|
}
|
|
|
|
// init initializes a new length codec.
|
|
func (lc *lengthCodec) init() {
|
|
for i := range lc.choice {
|
|
lc.choice[i] = probInit
|
|
}
|
|
for i := range lc.low {
|
|
lc.low[i] = makeTreeCodec(3)
|
|
}
|
|
for i := range lc.mid {
|
|
lc.mid[i] = makeTreeCodec(3)
|
|
}
|
|
lc.high = makeTreeCodec(8)
|
|
}
|
|
|
|
// Encode encodes the length offset. The length offset l can be compute by
|
|
// subtracting minMatchLen (2) from the actual length.
|
|
//
|
|
// l = length - minMatchLen
|
|
func (lc *lengthCodec) Encode(e *rangeEncoder, l uint32, posState uint32,
|
|
) (err error) {
|
|
if l > maxMatchLen-minMatchLen {
|
|
return errors.New("lengthCodec.Encode: l out of range")
|
|
}
|
|
if l < 8 {
|
|
if err = lc.choice[0].Encode(e, 0); err != nil {
|
|
return
|
|
}
|
|
return lc.low[posState].Encode(e, l)
|
|
}
|
|
if err = lc.choice[0].Encode(e, 1); err != nil {
|
|
return
|
|
}
|
|
if l < 16 {
|
|
if err = lc.choice[1].Encode(e, 0); err != nil {
|
|
return
|
|
}
|
|
return lc.mid[posState].Encode(e, l-8)
|
|
}
|
|
if err = lc.choice[1].Encode(e, 1); err != nil {
|
|
return
|
|
}
|
|
if err = lc.high.Encode(e, l-16); err != nil {
|
|
return
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// Decode reads the length offset. Add minMatchLen to compute the actual length
|
|
// to the length offset l.
|
|
func (lc *lengthCodec) Decode(d *rangeDecoder, posState uint32,
|
|
) (l uint32, err error) {
|
|
var b uint32
|
|
if b, err = lc.choice[0].Decode(d); err != nil {
|
|
return
|
|
}
|
|
if b == 0 {
|
|
l, err = lc.low[posState].Decode(d)
|
|
return
|
|
}
|
|
if b, err = lc.choice[1].Decode(d); err != nil {
|
|
return
|
|
}
|
|
if b == 0 {
|
|
l, err = lc.mid[posState].Decode(d)
|
|
l += 8
|
|
return
|
|
}
|
|
l, err = lc.high.Decode(d)
|
|
l += 16
|
|
return
|
|
}
|