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package rle
import (
"bytes"
"errors"
"github.com/ethereum/go-ethereum/crypto"
)
const (
token byte = 0xfe
emptyShaToken = 0xfd
emptyListShaToken = 0xfe
tokenToken = 0xff
)
var empty = crypto.Sha3([]byte(""))
var emptyList = crypto.Sha3([]byte{0x80})
func Decompress(dat []byte) ([]byte, error) {
buf := new(bytes.Buffer)
for i := 0; i < len(dat); i++ {
if dat[i] == token {
if i+1 < len(dat) {
switch dat[i+1] {
case emptyShaToken:
buf.Write(empty)
case emptyListShaToken:
buf.Write(emptyList)
case tokenToken:
buf.WriteByte(token)
default:
buf.Write(make([]byte, int(dat[i+1]-2)))
}
i++
} else {
return nil, errors.New("error reading bytes. token encountered without proceeding bytes")
}
} else {
buf.WriteByte(dat[i])
}
}
return buf.Bytes(), nil
}
func compressChunk(dat []byte) (ret []byte, n int) {
switch {
case dat[0] == token:
return []byte{token, tokenToken}, 1
case len(dat) > 1 && dat[0] == 0x0 && dat[1] == 0x0:
j := 0
for j <= 254 && j < len(dat) {
if dat[j] != 0 {
break
}
j++
}
return []byte{token, byte(j + 2)}, j
case len(dat) >= 32:
if dat[0] == empty[0] && bytes.Compare(dat[:32], empty) == 0 {
return []byte{token, emptyShaToken}, 32
} else if dat[0] == emptyList[0] && bytes.Compare(dat[:32], emptyList) == 0 {
return []byte{token, emptyListShaToken}, 32
}
fallthrough
default:
return dat[:1], 1
}
}
func Compress(dat []byte) []byte {
buf := new(bytes.Buffer)
i := 0
for i < len(dat) {
b, n := compressChunk(dat[i:])
buf.Write(b)
i += n
}
return buf.Bytes()
}
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