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