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package lz4ref
import (
"encoding/binary"
"fmt"
"math/bits"
"sync"
)
const (
// The following constants are used to setup the compression algorithm.
minMatch = 4 // the minimum size of the match sequence size (4 bytes)
winSizeLog = 16 // LZ4 64Kb window size limit
winSize = 1 << winSizeLog
winMask = winSize - 1 // 64Kb window of previous data for dependent blocks
// hashLog determines the size of the hash table used to quickly find a previous match position.
// Its value influences the compression speed and memory usage, the lower the faster,
// but at the expense of the compression ratio.
// 16 seems to be the best compromise for fast compression.
hashLog = 16
htSize = 1 << hashLog
mfLimit = 10 + minMatch // The last match cannot start within the last 14 bytes.
)
// blockHash hashes the lower five bytes of x into a value < htSize.
func blockHash(x uint64) uint32 {
const prime6bytes = 227718039650203
x &= 1<<40 - 1
return uint32((x * prime6bytes) >> (64 - hashLog))
}
func CompressBlockBound(n int) int {
return n + n/255 + 16
}
type Compressor struct {
// Offsets are at most 64kiB, so we can store only the lower 16 bits of
// match positions: effectively, an offset from some 64kiB block boundary.
//
// When we retrieve such an offset, we interpret it as relative to the last
// block boundary si &^ 0xffff, or the one before, (si &^ 0xffff) - 0x10000,
// depending on which of these is inside the current window. If a table
// entry was generated more than 64kiB back in the input, we find out by
// inspecting the input stream.
table [htSize]uint16
// Bitmap indicating which positions in the table are in use.
// This allows us to quickly reset the table for reuse,
// without having to zero everything.
inUse [htSize / 32]uint32
}
// Get returns the position of a presumptive match for the hash h.
// The match may be a false positive due to a hash collision or an old entry.
// If si < winSize, the return value may be negative.
func (c *Compressor) get(h uint32, si int) int {
h &= htSize - 1
i := 0
if c.inUse[h/32]&(1<<(h%32)) != 0 {
i = int(c.table[h])
}
i += si &^ winMask
if i >= si {
// Try previous 64kiB block (negative when in first block).
i -= winSize
}
return i
}
func (c *Compressor) put(h uint32, si int) {
h &= htSize - 1
c.table[h] = uint16(si)
c.inUse[h/32] |= 1 << (h % 32)
}
func (c *Compressor) reset() { c.inUse = [htSize / 32]uint32{} }
var compressorPool = sync.Pool{New: func() interface{} { return new(Compressor) }}
func CompressBlock(src, dst []byte) (int, error) {
c := compressorPool.Get().(*Compressor)
n, err := c.CompressBlock(src, dst)
compressorPool.Put(c)
return n, err
}
func CompressBlockLZ4s(src, dst []byte) (int, error) {
c := compressorPool.Get().(*Compressor)
n, err := c.CompressBlockLZ4s(src, dst)
compressorPool.Put(c)
return n, err
}
func (c *Compressor) CompressBlock(src, dst []byte) (int, error) {
// Zero out reused table to avoid non-deterministic output (issue #65).
c.reset()
const debug = false
if debug {
fmt.Printf("lz4 block start: len(src): %d, len(dst):%d \n", len(src), len(dst))
}
// Return 0, nil only if the destination buffer size is < CompressBlockBound.
isNotCompressible := len(dst) < CompressBlockBound(len(src))
// adaptSkipLog sets how quickly the compressor begins skipping blocks when data is incompressible.
// This significantly speeds up incompressible data and usually has very small impact on compression.
// bytes to skip = 1 + (bytes since last match >> adaptSkipLog)
const adaptSkipLog = 7
// si: Current position of the search.
// anchor: Position of the current literals.
var si, di, anchor int
sn := len(src) - mfLimit
if sn <= 0 {
goto lastLiterals
}
// Fast scan strategy: the hash table only stores the last five-byte sequences.
for si < sn {
// Hash the next five bytes (sequence)...
match := binary.LittleEndian.Uint64(src[si:])
h := blockHash(match)
h2 := blockHash(match >> 8)
// We check a match at s, s+1 and s+2 and pick the first one we get.
// Checking 3 only requires us to load the source one.
ref := c.get(h, si)
ref2 := c.get(h2, si+1)
c.put(h, si)
c.put(h2, si+1)
offset := si - ref
if offset <= 0 || offset >= winSize || uint32(match) != binary.LittleEndian.Uint32(src[ref:]) {
// No match. Start calculating another hash.
// The processor can usually do this out-of-order.
h = blockHash(match >> 16)
ref3 := c.get(h, si+2)
// Check the second match at si+1
si += 1
offset = si - ref2
if offset <= 0 || offset >= winSize || uint32(match>>8) != binary.LittleEndian.Uint32(src[ref2:]) {
// No match. Check the third match at si+2
si += 1
offset = si - ref3
c.put(h, si)
if offset <= 0 || offset >= winSize || uint32(match>>16) != binary.LittleEndian.Uint32(src[ref3:]) {
// Skip one extra byte (at si+3) before we check 3 matches again.
si += 2 + (si-anchor)>>adaptSkipLog
continue
}
}
}
// Match found.
lLen := si - anchor // Literal length.
// We already matched 4 bytes.
mLen := 4
// Extend backwards if we can, reducing literals.
tOff := si - offset - 1
for lLen > 0 && tOff >= 0 && src[si-1] == src[tOff] {
si--
tOff--
lLen--
mLen++
}
// Add the match length, so we continue search at the end.
// Use mLen to store the offset base.
si, mLen = si+mLen, si+minMatch
// Find the longest match by looking by batches of 8 bytes.
for si+8 <= sn {
x := binary.LittleEndian.Uint64(src[si:]) ^ binary.LittleEndian.Uint64(src[si-offset:])
if x == 0 {
si += 8
} else {
// Stop is first non-zero byte.
si += bits.TrailingZeros64(x) >> 3
break
}
}
mLen = si - mLen
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
if mLen < 0xF {
dst[di] = byte(mLen)
} else {
dst[di] = 0xF
}
// Encode literals length.
if debug {
fmt.Printf("emit %d literals\n", lLen)
}
if lLen < 0xF {
dst[di] |= byte(lLen << 4)
} else {
dst[di] |= 0xF0
di++
l := lLen - 0xF
for ; l >= 0xFF && di < len(dst); l -= 0xFF {
dst[di] = 0xFF
di++
}
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
dst[di] = byte(l)
}
di++
// Literals.
if di+lLen > len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
copy(dst[di:di+lLen], src[anchor:anchor+lLen])
di += lLen + 2
anchor = si
// Encode offset.
if debug {
fmt.Printf("emit copy, length: %d, offset: %d\n", mLen+minMatch, offset)
}
if di > len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
dst[di-2], dst[di-1] = byte(offset), byte(offset>>8)
// Encode match length part 2.
if mLen >= 0xF {
for mLen -= 0xF; mLen >= 0xFF && di < len(dst); mLen -= 0xFF {
dst[di] = 0xFF
di++
}
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
dst[di] = byte(mLen)
di++
}
// Check if we can load next values.
if si >= sn {
break
}
// Hash match end-2
h = blockHash(binary.LittleEndian.Uint64(src[si-2:]))
c.put(h, si-2)
}
lastLiterals:
if isNotCompressible && anchor == 0 {
// Incompressible.
return 0, nil
}
// Last literals.
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
lLen := len(src) - anchor
if lLen < 0xF {
dst[di] = byte(lLen << 4)
} else {
dst[di] = 0xF0
di++
for lLen -= 0xF; lLen >= 0xFF && di < len(dst); lLen -= 0xFF {
dst[di] = 0xFF
di++
}
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
dst[di] = byte(lLen)
}
di++
// Write the last literals.
if isNotCompressible && di >= anchor {
// Incompressible.
return 0, nil
}
if di+len(src)-anchor > len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
di += copy(dst[di:di+len(src)-anchor], src[anchor:])
return di, nil
}
func (c *Compressor) CompressBlockLZ4s(src, dst []byte) (int, error) {
// Zero out reused table to avoid non-deterministic output (issue #65).
c.reset()
const debug = false
const minMatch = 3
const addExtraLits = 32 // Suboptimal, but test emitting literals without matches. Set to 0 to disable.
if debug {
fmt.Printf("lz4 block start: len(src): %d, len(dst):%d \n", len(src), len(dst))
}
// Return 0, nil only if the destination buffer size is < CompressBlockBound.
isNotCompressible := len(dst) < CompressBlockBound(len(src))
// adaptSkipLog sets how quickly the compressor begins skipping blocks when data is incompressible.
// This significantly speeds up incompressible data and usually has very small impact on compression.
// bytes to skip = 1 + (bytes since last match >> adaptSkipLog)
const adaptSkipLog = 7
// si: Current position of the search.
// anchor: Position of the current literals.
var si, di, anchor int
sn := len(src) - mfLimit
if sn <= 0 {
goto lastLiterals
}
// Fast scan strategy: the hash table only stores the last five-byte sequences.
for si < sn {
// Hash the next five bytes (sequence)...
match := binary.LittleEndian.Uint64(src[si:])
h := blockHash(match)
h2 := blockHash(match >> 8)
// We check a match at s, s+1 and s+2 and pick the first one we get.
// Checking 3 only requires us to load the source one.
ref := c.get(h, si)
ref2 := c.get(h2, si+1)
c.put(h, si)
c.put(h2, si+1)
offset := si - ref
if offset <= 0 || offset >= winSize || uint32(match) != binary.LittleEndian.Uint32(src[ref:]) {
// No match. Start calculating another hash.
// The processor can usually do this out-of-order.
h = blockHash(match >> 16)
ref3 := c.get(h, si+2)
// Check the second match at si+1
si += 1
offset = si - ref2
if offset <= 0 || offset >= winSize || uint32(match>>8) != binary.LittleEndian.Uint32(src[ref2:]) {
// No match. Check the third match at si+2
si += 1
offset = si - ref3
c.put(h, si)
if offset <= 0 || offset >= winSize || uint32(match>>16) != binary.LittleEndian.Uint32(src[ref3:]) {
// Skip one extra byte (at si+3) before we check 3 matches again.
si += 2 + (si-anchor)>>adaptSkipLog
continue
}
}
}
// Match found.
lLen := si - anchor // Literal length.
// We already matched 4 bytes.
mLen := 4
// Extend backwards if we can, reducing literals.
tOff := si - offset - 1
for lLen > 0 && tOff >= 0 && src[si-1] == src[tOff] {
si--
tOff--
lLen--
mLen++
}
// Add the match length, so we continue search at the end.
// Use mLen to store the offset base.
si, mLen = si+mLen, si+minMatch
// Find the longest match by looking by batches of 8 bytes.
for si+8 <= sn {
x := binary.LittleEndian.Uint64(src[si:]) ^ binary.LittleEndian.Uint64(src[si-offset:])
if x == 0 {
si += 8
} else {
// Stop is first non-zero byte.
si += bits.TrailingZeros64(x) >> 3
break
}
}
if addExtraLits > 15 {
// Add X lits.
if lLen > addExtraLits {
dst[di] = 0xf0
dst[di+1] = byte(int(addExtraLits-15) & 0xff) // hack to compile
di += 2
copy(dst[di:di+addExtraLits], src[anchor:anchor+lLen])
di += addExtraLits
lLen -= addExtraLits
anchor += addExtraLits
}
}
mLen = si - mLen
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
if mLen < 0xF {
dst[di] = byte(mLen)
} else {
dst[di] = 0xF
}
// Encode literals length.
if debug {
fmt.Printf("emit %d literals\n", lLen)
}
if lLen < 0xF {
dst[di] |= byte(lLen << 4)
} else {
dst[di] |= 0xF0
di++
l := lLen - 0xF
for ; l >= 0xFF && di < len(dst); l -= 0xFF {
dst[di] = 0xFF
di++
}
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
dst[di] = byte(l)
}
di++
// Literals.
if di+lLen > len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
copy(dst[di:di+lLen], src[anchor:anchor+lLen])
di += lLen + 2
anchor = si
// Encode offset.
if debug {
fmt.Printf("emit copy, length: %d, offset: %d\n", mLen+minMatch, offset)
}
if di > len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
dst[di-2], dst[di-1] = byte(offset), byte(offset>>8)
// Encode match length part 2.
if mLen >= 0xF {
for mLen -= 0xF; mLen >= 0xFF && di < len(dst); mLen -= 0xFF {
dst[di] = 0xFF
di++
}
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
dst[di] = byte(mLen)
di++
}
// Check if we can load next values.
if si >= sn {
break
}
// Hash match end-2
h = blockHash(binary.LittleEndian.Uint64(src[si-2:]))
c.put(h, si-2)
}
lastLiterals:
if isNotCompressible && anchor == 0 {
// Incompressible.
return 0, nil
}
// Last literals.
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
lLen := len(src) - anchor
if lLen < 0xF {
dst[di] = byte(lLen << 4)
} else {
dst[di] = 0xF0
di++
for lLen -= 0xF; lLen >= 0xFF && di < len(dst); lLen -= 0xFF {
dst[di] = 0xFF
di++
}
if di >= len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
dst[di] = byte(lLen)
}
di++
// Write the last literals.
if isNotCompressible && di >= anchor {
// Incompressible.
return 0, nil
}
if di+len(src)-anchor > len(dst) {
return 0, ErrInvalidSourceShortBuffer
}
di += copy(dst[di:di+len(src)-anchor], src[anchor:])
return di, nil
}
func UncompressBlock(dst, src []byte) (ret int) {
// Restrict capacities so we don't read or write out of bounds.
dst = dst[:len(dst):len(dst)]
src = src[:len(src):len(src)]
const debug = false
const hasError = -2
if len(src) == 0 {
return hasError
}
defer func() {
if r := recover(); r != nil {
if debug {
fmt.Println("recover:", r)
}
ret = hasError
}
}()
var si, di uint
for {
if si >= uint(len(src)) {
return hasError
}
// Literals and match lengths (token).
b := uint(src[si])
si++
// Literals.
if lLen := b >> 4; lLen > 0 {
switch {
case lLen < 0xF && si+16 < uint(len(src)):
// Shortcut 1
// if we have enough room in src and dst, and the literals length
// is small enough (0..14) then copy all 16 bytes, even if not all
// are part of the literals.
copy(dst[di:], src[si:si+16])
si += lLen
di += lLen
if debug {
fmt.Println("ll:", lLen)
}
if mLen := b & 0xF; mLen < 0xF {
// Shortcut 2
// if the match length (4..18) fits within the literals, then copy
// all 18 bytes, even if not all are part of the literals.
mLen += 4
if offset := u16(src[si:]); mLen <= offset && offset < di {
i := di - offset
// The remaining buffer may not hold 18 bytes.
// See https://github.com/pierrec/lz4/issues/51.
if end := i + 18; end <= uint(len(dst)) {
copy(dst[di:], dst[i:end])
si += 2
di += mLen
continue
}
}
}
case lLen == 0xF:
for {
x := uint(src[si])
if lLen += x; int(lLen) < 0 {
if debug {
fmt.Println("int(lLen) < 0")
}
return hasError
}
si++
if x != 0xFF {
break
}
}
fallthrough
default:
copy(dst[di:di+lLen], src[si:si+lLen])
si += lLen
di += lLen
if debug {
fmt.Println("ll:", lLen)
}
}
}
mLen := b & 0xF
if si == uint(len(src)) && mLen == 0 {
break
} else if si >= uint(len(src))-2 {
return hasError
}
offset := u16(src[si:])
if offset == 0 {
return hasError
}
si += 2
// Match.
mLen += minMatch
if mLen == minMatch+0xF {
for {
x := uint(src[si])
if mLen += x; int(mLen) < 0 {
return hasError
}
si++
if x != 0xFF {
break
}
}
}
if debug {
fmt.Println("ml:", mLen, "offset:", offset)
}
// Copy the match.
if di < offset {
return hasError
}
expanded := dst[di-offset:]
if mLen > offset {
// Efficiently copy the match dst[di-offset:di] into the dst slice.
bytesToCopy := offset * (mLen / offset)
for n := offset; n <= bytesToCopy+offset; n *= 2 {
copy(expanded[n:], expanded[:n])
}
di += bytesToCopy
mLen -= bytesToCopy
}
di += uint(copy(dst[di:di+mLen], expanded[:mLen]))
}
return int(di)
}
func u16(p []byte) uint { return uint(binary.LittleEndian.Uint16(p)) }
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