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lzxpress.go
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lzxpress.go
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package prefetch
// Decompression algorithm reimplemented from Microsoft Reference here:
// https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-frs2/8cb5bae9-edf3-4833-9f0a-9d7e24218d3d
import (
"encoding/binary"
"errors"
"fmt"
"io"
"sort"
)
type BitStream struct {
// The input buffer.
source []byte
// The current byte offset into the source. As bits are drawn
// from the stream we backfill them at this position.
index int
mask uint32
bits uint32
}
func (self *BitStream) Lookup(n uint32) uint32 {
if n == 0 {
return 0
}
return self.mask >> (32 - n)
}
func (self *BitStream) Skip(n uint32) error {
self.mask <<= n
self.bits -= n
if self.bits < 16 {
if int(self.index+2) > len(self.source) {
return io.EOF
}
self.mask += uint32(binary.LittleEndian.Uint16(
self.source[self.index:self.index+2])) << (16 - self.bits)
self.index += 2
self.bits += 16
}
return nil
}
func NewBitStream(in []byte, in_pos int) *BitStream {
return &BitStream{
source: in,
mask: uint32(binary.LittleEndian.Uint16(in[in_pos:]))<<16 +
uint32(binary.LittleEndian.Uint16(in[in_pos+2:])),
index: in_pos + 4,
bits: 32,
}
}
type PREFIX_CODE_NODE struct {
id uint32
symbol uint32
leaf bool
child [2]*PREFIX_CODE_NODE
}
func (self PREFIX_CODE_NODE) String() string {
return fmt.Sprintf("Node %d: symbol %v leaf %v\n",
self.id, self.symbol, self.leaf)
}
type PREFIX_CODE_SYMBOL struct {
id uint32
symbol uint32
length uint32
}
func (self PREFIX_CODE_SYMBOL) String() string {
return fmt.Sprintf("Symbol %d: symbol %v length %v\n",
self.id, self.symbol, self.length)
}
/*
inout PREFIX_CODE_NODE treeNodes[1024]: A 1024 element
PREFIX_CODE_NODE array that contains the Huffman prefix code
tree's nodes.
in ULONG leafIndex: The index in treeNodes of the node to link into the tree.
in ULONG mask: The symbol's prefix code.
in ULONG bits: The number of bits in the symbol's prefix code.
Return Value
Returns the index in treeNodes of the next node to be processed.
*/
func PrefixCodeTreeAddLeaf(
treeNodes []PREFIX_CODE_NODE,
leafIndex uint32,
mask uint32,
bits uint32) uint32 {
node := &treeNodes[0]
i := leafIndex + 1
childIndex := uint32(0)
for bits > 1 {
bits = bits - 1
childIndex = (mask >> bits) & 1
if node.child[childIndex] == nil {
node.child[childIndex] = &treeNodes[i]
treeNodes[i].leaf = false
i++
}
node = node.child[childIndex]
}
node.child[mask&1] = &treeNodes[leafIndex]
return i
}
func PrefixCodeTreeRebuild(input []byte) *PREFIX_CODE_NODE {
treeNodes := make([]PREFIX_CODE_NODE, 1024)
symbolInfo := make([]PREFIX_CODE_SYMBOL, 512)
for i := 0; i < 256; i++ {
value := input[i]
symbolInfo[2*i].id = uint32(2 * i)
symbolInfo[2*i].symbol = uint32(2 * i)
symbolInfo[2*i].length = uint32(value & 0xf)
value >>= 4
symbolInfo[2*i+1].id = uint32(2*i + 1)
symbolInfo[2*i+1].symbol = uint32(2*i + 1)
symbolInfo[2*i+1].length = uint32(value & 0xf)
}
sort.SliceStable(symbolInfo, func(i, j int) bool {
a := symbolInfo[i]
b := symbolInfo[j]
if a.length < b.length {
return true
}
if a.symbol < b.symbol {
return true
}
return false
})
i := 0
for i < 512 && symbolInfo[i].length == 0 {
i++
}
mask := uint32(0)
bits := uint32(1)
root := &treeNodes[0]
root.leaf = false
j := uint32(1)
for ; i < 512; i++ {
treeNodes[j].id = uint32(j)
treeNodes[j].symbol = symbolInfo[i].symbol
treeNodes[j].leaf = true
mask = mask << (symbolInfo[i].length - bits)
bits = symbolInfo[i].length
j = PrefixCodeTreeAddLeaf(treeNodes, j, mask, bits)
mask++
}
return root
}
func PrefixCodeTreeDecodeSymbol(bstr *BitStream, root *PREFIX_CODE_NODE) (
uint32, error) {
node := root
for {
bit := bstr.Lookup(1)
err := bstr.Skip(1)
if err != nil {
return 0, err
}
node = node.child[bit]
if node == nil {
return 0, errors.New("Corruption detected")
}
if node.leaf {
break
}
}
return node.symbol, nil
}
func LZXpressHuffmanDecompressChunk(
in_idx int, // Current cursor in the input buffer.
input []byte, // Input buffer.
out_idx int, // Cursor cursor on the output buffer.
output []byte, // The output buffer.
chunk_size int, // The required size of uncompressed buffer
) (int, int, error) {
// There must be at least this many bytes available to read.
if in_idx+256 > len(input) {
return 0, 0, io.EOF
}
root := PrefixCodeTreeRebuild(input[in_idx:])
bstr := NewBitStream(input, in_idx+256)
i := out_idx
for i < out_idx+chunk_size {
symbol, err := PrefixCodeTreeDecodeSymbol(bstr, root)
if err != nil {
if err == io.EOF {
err = nil
}
return int(bstr.index), i, err
}
if symbol < 256 {
output[i] = byte(symbol)
i++
} else {
symbol -= 256
length := uint32(symbol & 15)
symbol >>= 4
offset := int32(0)
if symbol != 0 {
offset = int32(bstr.Lookup(symbol))
}
offset |= 1 << symbol
offset = -offset
if length == 15 {
length = uint32(bstr.source[bstr.index]) + 15
bstr.index = bstr.index + 1
if length == 270 {
length = uint32(binary.LittleEndian.Uint16(
bstr.source[bstr.index:]))
bstr.index = bstr.index + 2
}
}
err := bstr.Skip(symbol)
if err != nil {
return int(bstr.index), i, err
}
length = length + 3
for {
if i+int(offset) < 0 {
return int(bstr.index),
i, errors.New("Decompression error")
}
output[i] = output[i+int(offset)]
i++
length -= 1
if length == 0 {
break
}
}
}
}
return int(bstr.index), i, nil
}
// https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-frs2/8cb5bae9-edf3-4833-9f0a-9d7e24218d3d
func LZXpressHuffmanDecompress(input []byte, output_size int) ([]byte, error) {
output := make([]byte, output_size)
var err error
// Index into the input buffer.
in_idx := 0
// Index into the output buffer.
out_idx := 0
for {
// How much data belongs in the current chunk. Chunks
// are split into maximum 65536 bytes.
chunk_size := output_size - out_idx
if chunk_size > 65536 {
chunk_size = 65536
}
in_idx, out_idx, err = LZXpressHuffmanDecompressChunk(
in_idx, input, out_idx, output, chunk_size)
if err != nil {
return output, err
}
// We are done.
if out_idx >= len(output) || in_idx >= len(input) {
break
}
}
return output, nil
}