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69 lines
1.8 KiB
69 lines
1.8 KiB
// Copyright 2014-2017 Ulrich Kunitz. 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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import (
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"errors"
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"fmt"
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)
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// maximum and minimum values for the LZMA properties.
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const (
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minPB = 0
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maxPB = 4
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)
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// maxPropertyCode is the possible maximum of a properties code byte.
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const maxPropertyCode = (maxPB+1)*(maxLP+1)*(maxLC+1) - 1
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// Properties contains the parameters LC, LP and PB. The parameter LC
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// defines the number of literal context bits; parameter LP the number
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// of literal position bits and PB the number of position bits.
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type Properties struct {
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LC int
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LP int
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PB int
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}
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// String returns the properties in a string representation.
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func (p *Properties) String() string {
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return fmt.Sprintf("LC %d LP %d PB %d", p.LC, p.LP, p.PB)
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}
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// PropertiesForCode converts a properties code byte into a Properties value.
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func PropertiesForCode(code byte) (p Properties, err error) {
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if code > maxPropertyCode {
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return p, errors.New("lzma: invalid properties code")
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}
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p.LC = int(code % 9)
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code /= 9
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p.LP = int(code % 5)
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code /= 5
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p.PB = int(code % 5)
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return p, err
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}
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// verify checks the properties for correctness.
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func (p *Properties) verify() error {
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if p == nil {
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return errors.New("lzma: properties are nil")
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}
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if !(minLC <= p.LC && p.LC <= maxLC) {
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return errors.New("lzma: lc out of range")
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}
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if !(minLP <= p.LP && p.LP <= maxLP) {
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return errors.New("lzma: lp out of range")
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}
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if !(minPB <= p.PB && p.PB <= maxPB) {
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return errors.New("lzma: pb out of range")
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}
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return nil
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}
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// Code converts the properties to a byte. The function assumes that
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// the properties components are all in range.
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func (p Properties) Code() byte {
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return byte((p.PB*5+p.LP)*9 + p.LC)
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}
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