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55 lines
1.1 KiB
55 lines
1.1 KiB
/*
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* Delta decoder
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*
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* Author: Lasse Collin <lasse.collin@tukaani.org>
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*
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* Translation to Go: Michael Cross <https://github.com/xi2>
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*
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* This file has been put into the public domain.
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* You can do whatever you want with this file.
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*/
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package xz
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type xzDecDelta struct {
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delta [256]byte
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pos byte
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distance int // in range [1, 256]
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}
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/*
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* Decode raw stream which has a delta filter as the first filter.
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*/
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func xzDecDeltaRun(s *xzDecDelta, b *xzBuf, chain func(*xzBuf) xzRet) xzRet {
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outStart := b.outPos
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ret := chain(b)
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for i := outStart; i < b.outPos; i++ {
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tmp := b.out[i] + s.delta[byte(s.distance+int(s.pos))]
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s.delta[s.pos] = tmp
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b.out[i] = tmp
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s.pos--
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}
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return ret
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}
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/*
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* Allocate memory for a delta decoder. xzDecDeltaReset must be used
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* before calling xzDecDeltaRun.
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*/
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func xzDecDeltaCreate() *xzDecDelta {
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return new(xzDecDelta)
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}
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/*
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* Returns xzOK if the given distance is valid. Otherwise
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* xzOptionsError is returned.
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*/
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func xzDecDeltaReset(s *xzDecDelta, distance int) xzRet {
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if distance < 1 || distance > 256 {
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return xzOptionsError
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}
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s.delta = [256]byte{}
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s.pos = 0
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s.distance = distance
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return xzOK
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}
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