cri-o/vendor/github.com/Microsoft/go-winio/wim/lzx/lzx.go

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// Package lzx implements a decompressor for the the WIM variant of the
// LZX compression algorithm.
//
// The LZX algorithm is an earlier variant of LZX DELTA, which is documented
// at https://msdn.microsoft.com/en-us/library/cc483133(v=exchg.80).aspx.
package lzx
import (
"bytes"
"encoding/binary"
"errors"
"io"
)
const (
maincodecount = 496
maincodesplit = 256
lencodecount = 249
lenshift = 9
codemask = 0x1ff
tablebits = 9
tablesize = 1 << tablebits
maxBlockSize = 32768
windowSize = 32768
maxTreePathLen = 16
e8filesize = 12000000
maxe8offset = 0x3fffffff
verbatimBlock = 1
alignedOffsetBlock = 2
uncompressedBlock = 3
)
var footerBits = [...]byte{
0, 0, 0, 0, 1, 1, 2, 2,
3, 3, 4, 4, 5, 5, 6, 6,
7, 7, 8, 8, 9, 9, 10, 10,
11, 11, 12, 12, 13, 13, 14,
}
var basePosition = [...]uint16{
0, 1, 2, 3, 4, 6, 8, 12,
16, 24, 32, 48, 64, 96, 128, 192,
256, 384, 512, 768, 1024, 1536, 2048, 3072,
4096, 6144, 8192, 12288, 16384, 24576, 32768,
}
var (
errCorrupt = errors.New("LZX data corrupt")
)
// Reader is an interface used by the decompressor to access
// the input stream. If the provided io.Reader does not implement
// Reader, then a bufio.Reader is used.
type Reader interface {
io.Reader
io.ByteReader
}
type decompressor struct {
r io.Reader
err error
unaligned bool
nbits byte
c uint32
lru [3]uint16
uncompressed int
windowReader *bytes.Reader
mainlens [maincodecount]byte
lenlens [lencodecount]byte
window [windowSize]byte
b []byte
bv int
bo int
}
//go:noinline
func (f *decompressor) fail(err error) {
if f.err == nil {
f.err = err
}
f.bo = 0
f.bv = 0
}
func (f *decompressor) ensureAtLeast(n int) error {
if f.bv-f.bo >= n {
return nil
}
if f.err != nil {
return f.err
}
if f.bv != f.bo {
copy(f.b[:f.bv-f.bo], f.b[f.bo:f.bv])
}
n, err := io.ReadAtLeast(f.r, f.b[f.bv-f.bo:], n)
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
} else {
f.fail(err)
}
return err
}
f.bv = f.bv - f.bo + n
f.bo = 0
return nil
}
// feed retrieves another 16-bit word from the stream and consumes
// it into f.c. It returns false if there are no more bytes available.
// Otherwise, on error, it sets f.err.
func (f *decompressor) feed() bool {
err := f.ensureAtLeast(2)
if err != nil {
if err == io.ErrUnexpectedEOF {
return false
}
}
f.c |= (uint32(f.b[f.bo+1])<<8 | uint32(f.b[f.bo])) << (16 - f.nbits)
f.nbits += 16
f.bo += 2
return true
}
// getBits retrieves the next n bits from the byte stream. n
// must be <= 16. It sets f.err on error.
func (f *decompressor) getBits(n byte) uint16 {
if f.nbits < n {
if !f.feed() {
f.fail(io.ErrUnexpectedEOF)
}
}
c := uint16(f.c >> (32 - n))
f.c <<= n
f.nbits -= n
return c
}
type huffman struct {
extra [][]uint16
maxbits byte
table [tablesize]uint16
}
// buildTable builds a huffman decoding table from a slice of code lengths,
// one per code, in order. Each code length must be <= maxTreePathLen.
// See https://en.wikipedia.org/wiki/Canonical_Huffman_code.
func buildTable(codelens []byte) *huffman {
// Determine the number of codes of each length, and the
// maximum length.
var count [maxTreePathLen + 1]uint
var max byte
for _, cl := range codelens {
count[cl]++
if max < cl {
max = cl
}
}
if max == 0 {
return &huffman{}
}
// Determine the first code of each length.
var first [maxTreePathLen + 1]uint
code := uint(0)
for i := byte(1); i <= max; i++ {
code <<= 1
first[i] = code
code += count[i]
}
if code != 1<<max {
return nil
}
// Build a table for code lookup. For code sizes < max,
// put all possible suffixes for the code into the table, too.
// For max > tablebits, split long codes into additional tables
// of suffixes of max-tablebits length.
h := &huffman{maxbits: max}
if max > tablebits {
core := first[tablebits+1] / 2 // Number of codes that fit without extra tables
nextra := 1<<tablebits - core // Number of extra entries
h.extra = make([][]uint16, nextra)
for code := core; code < 1<<tablebits; code++ {
h.table[code] = uint16(code - core)
h.extra[code-core] = make([]uint16, 1<<(max-tablebits))
}
}
for i, cl := range codelens {
if cl != 0 {
code := first[cl]
first[cl]++
v := uint16(cl)<<lenshift | uint16(i)
if cl <= tablebits {
extendedCode := code << (tablebits - cl)
for j := uint(0); j < 1<<(tablebits-cl); j++ {
h.table[extendedCode+j] = v
}
} else {
prefix := code >> (cl - tablebits)
suffix := code & (1<<(cl-tablebits) - 1)
extendedCode := suffix << (max - cl)
for j := uint(0); j < 1<<(max-cl); j++ {
h.extra[h.table[prefix]][extendedCode+j] = v
}
}
}
}
return h
}
// getCode retrieves the next code using the provided
// huffman tree. It sets f.err on error.
func (f *decompressor) getCode(h *huffman) uint16 {
if h.maxbits > 0 {
if f.nbits < maxTreePathLen {
f.feed()
}
// For codes with length < tablebits, it doesn't matter
// what the remainder of the bits used for table lookup
// are, since entries with all possible suffixes were
// added to the table.
c := h.table[f.c>>(32-tablebits)]
if c >= 1<<lenshift {
// The code is already in c.
} else {
c = h.extra[c][f.c<<tablebits>>(32-(h.maxbits-tablebits))]
}
n := byte(c >> lenshift)
if f.nbits >= n {
// Only consume the length of the code, not the maximum
// code length.
f.c <<= n
f.nbits -= n
return c & codemask
}
f.fail(io.ErrUnexpectedEOF)
return 0
}
// This is an empty tree. It should not be used.
f.fail(errCorrupt)
return 0
}
// mod17 computes the value mod 17.
func mod17(b byte) byte {
for b >= 17 {
b -= 17
}
return b
}
// readTree updates the huffman tree path lengths in lens by
// reading and decoding lengths from the byte stream. lens
// should be prepopulated with the previous block's tree's path
// lengths. For the first block, lens should be zero.
func (f *decompressor) readTree(lens []byte) error {
// Get the pre-tree for the main tree.
var pretreeLen [20]byte
for i := range pretreeLen {
pretreeLen[i] = byte(f.getBits(4))
}
if f.err != nil {
return f.err
}
h := buildTable(pretreeLen[:])
// The lengths are encoded as a series of huffman codes
// encoded by the pre-tree.
for i := 0; i < len(lens); {
c := byte(f.getCode(h))
if f.err != nil {
return f.err
}
switch {
case c <= 16: // length is delta from previous length
lens[i] = mod17(lens[i] + 17 - c)
i++
case c == 17: // next n + 4 lengths are zero
zeroes := int(f.getBits(4)) + 4
if i+zeroes > len(lens) {
return errCorrupt
}
for j := 0; j < zeroes; j++ {
lens[i+j] = 0
}
i += zeroes
case c == 18: // next n + 20 lengths are zero
zeroes := int(f.getBits(5)) + 20
if i+zeroes > len(lens) {
return errCorrupt
}
for j := 0; j < zeroes; j++ {
lens[i+j] = 0
}
i += zeroes
case c == 19: // next n + 4 lengths all have the same value
same := int(f.getBits(1)) + 4
if i+same > len(lens) {
return errCorrupt
}
c = byte(f.getCode(h))
if c > 16 {
return errCorrupt
}
l := mod17(lens[i] + 17 - c)
for j := 0; j < same; j++ {
lens[i+j] = l
}
i += same
default:
return errCorrupt
}
}
if f.err != nil {
return f.err
}
return nil
}
func (f *decompressor) readBlockHeader() (byte, uint16, error) {
// If the previous block was an unaligned uncompressed block, restore
// 2-byte alignment.
if f.unaligned {
err := f.ensureAtLeast(1)
if err != nil {
return 0, 0, err
}
f.bo++
f.unaligned = false
}
blockType := f.getBits(3)
full := f.getBits(1)
var blockSize uint16
if full != 0 {
blockSize = maxBlockSize
} else {
blockSize = f.getBits(16)
if blockSize > maxBlockSize {
return 0, 0, errCorrupt
}
}
if f.err != nil {
return 0, 0, f.err
}
switch blockType {
case verbatimBlock, alignedOffsetBlock:
// The caller will read the huffman trees.
case uncompressedBlock:
if f.nbits > 16 {
panic("impossible: more than one 16-bit word remains")
}
// Drop the remaining bits in the current 16-bit word
// If there are no bits left, discard a full 16-bit word.
n := f.nbits
if n == 0 {
n = 16
}
f.getBits(n)
// Read the LRU values for the next block.
err := f.ensureAtLeast(12)
if err != nil {
return 0, 0, err
}
f.lru[0] = uint16(binary.LittleEndian.Uint32(f.b[f.bo : f.bo+4]))
f.lru[1] = uint16(binary.LittleEndian.Uint32(f.b[f.bo+4 : f.bo+8]))
f.lru[2] = uint16(binary.LittleEndian.Uint32(f.b[f.bo+8 : f.bo+12]))
f.bo += 12
default:
return 0, 0, errCorrupt
}
return byte(blockType), blockSize, nil
}
// readTrees reads the two or three huffman trees for the current block.
// readAligned specifies whether to read the aligned offset tree.
func (f *decompressor) readTrees(readAligned bool) (main *huffman, length *huffman, aligned *huffman, err error) {
// Aligned offset blocks start with a small aligned offset tree.
if readAligned {
var alignedLen [8]byte
for i := range alignedLen {
alignedLen[i] = byte(f.getBits(3))
}
aligned = buildTable(alignedLen[:])
if aligned == nil {
err = errors.New("corrupt")
return
}
}
// The main tree is encoded in two parts.
err = f.readTree(f.mainlens[:maincodesplit])
if err != nil {
return
}
err = f.readTree(f.mainlens[maincodesplit:])
if err != nil {
return
}
main = buildTable(f.mainlens[:])
if main == nil {
err = errors.New("corrupt")
return
}
// The length tree is encoding in a single part.
err = f.readTree(f.lenlens[:])
if err != nil {
return
}
length = buildTable(f.lenlens[:])
if length == nil {
err = errors.New("corrupt")
return
}
err = f.err
return
}
// readCompressedBlock decodes a compressed block, writing into the window
// starting at start and ending at end, and using the provided huffman trees.
func (f *decompressor) readCompressedBlock(start, end uint16, hmain, hlength, haligned *huffman) (int, error) {
i := start
for i < end {
main := f.getCode(hmain)
if f.err != nil {
break
}
if main < 256 {
// Literal byte.
f.window[i] = byte(main)
i++
continue
}
// This is a match backward in the window. Determine
// the offset and dlength.
matchlen := (main - 256) % 8
slot := (main - 256) / 8
// The length is either the low bits of the code,
// or if this is 7, is encoded with the length tree.
if matchlen == 7 {
matchlen += f.getCode(hlength)
}
matchlen += 2
var matchoffset uint16
if slot < 3 {
// The offset is one of the LRU values.
matchoffset = f.lru[slot]
f.lru[slot] = f.lru[0]
f.lru[0] = matchoffset
} else {
// The offset is encoded as a combination of the
// slot and more bits from the bit stream.
offsetbits := footerBits[slot]
var verbatimbits, alignedbits uint16
if offsetbits > 0 {
if haligned != nil && offsetbits >= 3 {
// This is an aligned offset block. Combine
// the bits written verbatim with the aligned
// offset tree code.
verbatimbits = f.getBits(offsetbits-3) * 8
alignedbits = f.getCode(haligned)
} else {
// There are no aligned offset bits to read,
// only verbatim bits.
verbatimbits = f.getBits(offsetbits)
alignedbits = 0
}
}
matchoffset = basePosition[slot] + verbatimbits + alignedbits - 2
// Update the LRU cache.
f.lru[2] = f.lru[1]
f.lru[1] = f.lru[0]
f.lru[0] = matchoffset
}
if matchoffset <= i && matchlen <= end-i {
copyend := i + matchlen
for ; i < copyend; i++ {
f.window[i] = f.window[i-matchoffset]
}
} else {
f.fail(errCorrupt)
break
}
}
return int(i - start), f.err
}
// readBlock decodes the current block and returns the number of uncompressed bytes.
func (f *decompressor) readBlock(start uint16) (int, error) {
blockType, size, err := f.readBlockHeader()
if err != nil {
return 0, err
}
if blockType == uncompressedBlock {
if size%2 == 1 {
// Remember to realign the byte stream at the next block.
f.unaligned = true
}
copied := 0
if f.bo < f.bv {
copied = int(size)
s := int(start)
if copied > f.bv-f.bo {
copied = f.bv - f.bo
}
copy(f.window[s:s+copied], f.b[f.bo:f.bo+copied])
f.bo += copied
}
n, err := io.ReadFull(f.r, f.window[start+uint16(copied):start+size])
return copied + n, err
}
hmain, hlength, haligned, err := f.readTrees(blockType == alignedOffsetBlock)
if err != nil {
return 0, err
}
return f.readCompressedBlock(start, start+size, hmain, hlength, haligned)
}
// decodeE8 reverses the 0xe8 x86 instruction encoding that was performed
// to the uncompressed data before it was compressed.
func decodeE8(b []byte, off int64) {
if off > maxe8offset || len(b) < 10 {
return
}
for i := 0; i < len(b)-10; i++ {
if b[i] == 0xe8 {
currentPtr := int32(off) + int32(i)
abs := int32(binary.LittleEndian.Uint32(b[i+1 : i+5]))
if abs >= -currentPtr && abs < e8filesize {
var rel int32
if abs >= 0 {
rel = abs - currentPtr
} else {
rel = abs + e8filesize
}
binary.LittleEndian.PutUint32(b[i+1:i+5], uint32(rel))
}
i += 4
}
}
}
func (f *decompressor) Read(b []byte) (int, error) {
// Read and uncompress everything.
if f.windowReader == nil {
n := 0
for n < f.uncompressed {
k, err := f.readBlock(uint16(n))
if err != nil {
return 0, err
}
n += k
}
decodeE8(f.window[:f.uncompressed], 0)
f.windowReader = bytes.NewReader(f.window[:f.uncompressed])
}
// Just read directly from the window.
return f.windowReader.Read(b)
}
func (f *decompressor) Close() error {
return nil
}
// NewReader returns a new io.ReadCloser that decompresses a
// WIM LZX stream until uncompressedSize bytes have been returned.
func NewReader(r io.Reader, uncompressedSize int) (io.ReadCloser, error) {
if uncompressedSize > windowSize {
return nil, errors.New("uncompressed size is limited to 32KB")
}
f := &decompressor{
lru: [3]uint16{1, 1, 1},
uncompressed: uncompressedSize,
b: make([]byte, 4096),
r: r,
}
return f, nil
}