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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 Compress(dat []byte) []byte {
buf := new(bytes.Buffer)
for i := 0; i < len(dat); i++ {
if dat[i] == token {
buf.Write([]byte{token, tokenToken})
} else if i+1 < len(dat) {
if dat[i] == 0x0 && dat[i+1] == 0x0 {
j := 0
for j <= 254 && i+j < len(dat) {
if dat[i+j] != 0 {
break
}
j++
}
buf.Write([]byte{token, byte(j + 2)})
i += (j - 1)
} else if len(dat[i:]) >= 32 {
if dat[i] == empty[0] && bytes.Compare(dat[i:i+32], empty) == 0 {
buf.Write([]byte{token, emptyShaToken})
i += 31
} else if dat[i] == emptyList[0] && bytes.Compare(dat[i:i+32], emptyList) == 0 {
buf.Write([]byte{token, emptyListShaToken})
i += 31
} else {
buf.WriteByte(dat[i])
}
} else {
buf.WriteByte(dat[i])
}
} else {
buf.WriteByte(dat[i])
}
}
return buf.Bytes()
}
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