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.
54 lines
1.5 KiB
Go
54 lines
1.5 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
|
|
|
|
// movebits defines the number of bits used for the updates of probability
|
|
// values.
|
|
const movebits = 5
|
|
|
|
// probbits defines the number of bits of a probability value.
|
|
const probbits = 11
|
|
|
|
// probInit defines 0.5 as initial value for prob values.
|
|
const probInit prob = 1 << (probbits - 1)
|
|
|
|
// Type prob represents probabilities. The type can also be used to encode and
|
|
// decode single bits.
|
|
type prob uint16
|
|
|
|
// Dec decreases the probability. The decrease is proportional to the
|
|
// probability value.
|
|
func (p *prob) dec() {
|
|
*p -= *p >> movebits
|
|
}
|
|
|
|
// Inc increases the probability. The Increase is proportional to the
|
|
// difference of 1 and the probability value.
|
|
func (p *prob) inc() {
|
|
*p += ((1 << probbits) - *p) >> movebits
|
|
}
|
|
|
|
// Computes the new bound for a given range using the probability value.
|
|
func (p prob) bound(r uint32) uint32 {
|
|
return (r >> probbits) * uint32(p)
|
|
}
|
|
|
|
// Bits returns 1. One is the number of bits that can be encoded or decoded
|
|
// with a single prob value.
|
|
func (p prob) Bits() int {
|
|
return 1
|
|
}
|
|
|
|
// Encode encodes the least-significant bit of v. Note that the p value will be
|
|
// changed.
|
|
func (p *prob) Encode(e *rangeEncoder, v uint32) error {
|
|
return e.EncodeBit(v, p)
|
|
}
|
|
|
|
// Decode decodes a single bit. Note that the p value will change.
|
|
func (p *prob) Decode(d *rangeDecoder) (v uint32, err error) {
|
|
return d.DecodeBit(p)
|
|
}
|