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/*
* Copyright 2011-2012 Branimir Karadzic. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY COPYRIGHT HOLDER ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
* SHALL COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
package lz4
import (
"encoding/binary"
"errors"
"io"
)
var (
// ErrCorrupt indicates the input was corrupt
ErrCorrupt = errors.New("corrupt input")
)
const (
mlBits = 4
mlMask = (1 << mlBits) - 1
runBits = 8 - mlBits
runMask = (1 << runBits) - 1
)
type decoder struct {
src []byte
dst []byte
spos uint32
dpos uint32
ref uint32
}
func (d *decoder) readByte() (uint8, error) {
if int(d.spos) == len(d.src) {
return 0, io.EOF
}
b := d.src[d.spos]
d.spos++
return b, nil
}
func (d *decoder) getLen() (uint32, error) {
length := uint32(0)
ln, err := d.readByte()
if err != nil {
return 0, ErrCorrupt
}
for ln == 255 {
length += 255
ln, err = d.readByte()
if err != nil {
return 0, ErrCorrupt
}
}
length += uint32(ln)
return length, nil
}
func (d *decoder) cp(length, decr uint32) {
if int(d.ref+length) < int(d.dpos) {
copy(d.dst[d.dpos:], d.dst[d.ref:d.ref+length])
} else {
for ii := uint32(0); ii < length; ii++ {
d.dst[d.dpos+ii] = d.dst[d.ref+ii]
}
}
d.dpos += length
d.ref += length - decr
}
func (d *decoder) finish(err error) error {
if err == io.EOF {
return nil
}
return err
}
// Decode returns the decoded form of src. The returned slice may be a
// subslice of dst if it was large enough to hold the entire decoded block.
func Decode(dst, src []byte) ([]byte, error) {
if len(src) < 4 {
return nil, ErrCorrupt
}
uncompressedLen := binary.LittleEndian.Uint32(src)
if uncompressedLen == 0 {
return nil, nil
}
if uncompressedLen > MaxInputSize {
return nil, ErrTooLarge
}
if dst == nil || len(dst) < int(uncompressedLen) {
dst = make([]byte, uncompressedLen)
}
d := decoder{src: src, dst: dst[:uncompressedLen], spos: 4}
decr := []uint32{0, 3, 2, 3}
for {
code, err := d.readByte()
if err != nil {
return d.dst, d.finish(err)
}
length := uint32(code >> mlBits)
if length == runMask {
ln, err := d.getLen()
if err != nil {
return nil, ErrCorrupt
}
length += ln
}
if int(d.spos+length) > len(d.src) || int(d.dpos+length) > len(d.dst) {
return nil, ErrCorrupt
}
for ii := uint32(0); ii < length; ii++ {
d.dst[d.dpos+ii] = d.src[d.spos+ii]
}
d.spos += length
d.dpos += length
if int(d.spos) == len(d.src) {
return d.dst, nil
}
if int(d.spos+2) >= len(d.src) {
return nil, ErrCorrupt
}
back := uint32(d.src[d.spos]) | uint32(d.src[d.spos+1])<<8
if back > d.dpos {
return nil, ErrCorrupt
}
d.spos += 2
d.ref = d.dpos - back
length = uint32(code & mlMask)
if length == mlMask {
ln, err := d.getLen()
if err != nil {
return nil, ErrCorrupt
}
length += ln
}
literal := d.dpos - d.ref
if literal < 4 {
if int(d.dpos+4) > len(d.dst) {
return nil, ErrCorrupt
}
d.cp(4, decr[literal])
} else {
length += 4
}
if d.dpos+length > uncompressedLen {
return nil, ErrCorrupt
}
d.cp(length, 0)
}
}
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