open-vault/vendor/github.com/pierrec/lz4/block.go
Jeff Mitchell 9ebc57581d
Switch to go modules (#6585)
* Switch to go modules

* Make fmt
2019-04-13 03:44:06 -04:00

398 lines
8.9 KiB
Go

package lz4
import (
"encoding/binary"
"errors"
)
var (
// ErrInvalidSourceShortBuffer is returned by UncompressBlock or CompressBLock when a compressed
// block is corrupted or the destination buffer is not large enough for the uncompressed data.
ErrInvalidSourceShortBuffer = errors.New("lz4: invalid source or destination buffer too short")
// ErrInvalid is returned when reading an invalid LZ4 archive.
ErrInvalid = errors.New("lz4: bad magic number")
)
// blockHash hashes 4 bytes into a value < winSize.
func blockHash(x uint32) uint32 {
const hasher uint32 = 2654435761 // Knuth multiplicative hash.
return x * hasher >> hashShift
}
// CompressBlockBound returns the maximum size of a given buffer of size n, when not compressible.
func CompressBlockBound(n int) int {
return n + n/255 + 16
}
// UncompressBlock uncompresses the source buffer into the destination one,
// and returns the uncompressed size.
//
// The destination buffer must be sized appropriately.
//
// An error is returned if the source data is invalid or the destination buffer is too small.
func UncompressBlock(src, dst []byte) (si int, err error) {
defer func() {
// It is now faster to let the runtime panic and recover on out of bound slice access
// than checking indices as we go along.
if recover() != nil {
err = ErrInvalidSourceShortBuffer
}
}()
sn := len(src)
if sn == 0 {
return 0, nil
}
var di int
for {
// Literals and match lengths (token).
b := int(src[si])
si++
// Literals.
if lLen := b >> 4; lLen > 0 {
if lLen == 0xF {
for src[si] == 0xFF {
lLen += 0xFF
si++
}
lLen += int(src[si])
si++
}
i := si
si += lLen
di += copy(dst[di:], src[i:si])
if si >= sn {
return di, nil
}
}
si++
_ = src[si] // Bound check elimination.
offset := int(src[si-1]) | int(src[si])<<8
si++
// Match.
mLen := b & 0xF
if mLen == 0xF {
for src[si] == 0xFF {
mLen += 0xFF
si++
}
mLen += int(src[si])
si++
}
mLen += minMatch
// Copy the match.
i := di - offset
if offset > 0 && mLen >= offset {
// Efficiently copy the match dst[di-offset:di] into the dst slice.
bytesToCopy := offset * (mLen / offset)
expanded := dst[i:]
for n := offset; n <= bytesToCopy+offset; n *= 2 {
copy(expanded[n:], expanded[:n])
}
di += bytesToCopy
mLen -= bytesToCopy
}
di += copy(dst[di:], dst[i:i+mLen])
}
}
// CompressBlock compresses the source buffer into the destination one.
// This is the fast version of LZ4 compression and also the default one.
// The size of hashTable must be at least 64Kb.
//
// The size of the compressed data is returned. If it is 0 and no error, then the data is incompressible.
//
// An error is returned if the destination buffer is too small.
func CompressBlock(src, dst []byte, hashTable []int) (di int, err error) {
defer func() {
if recover() != nil {
err = ErrInvalidSourceShortBuffer
}
}()
sn, dn := len(src)-mfLimit, len(dst)
if sn <= 0 || dn == 0 {
return 0, nil
}
var si int
// Fast scan strategy: the hash table only stores the last 4 bytes sequences.
// const accInit = 1 << skipStrength
anchor := si // Position of the current literals.
// acc := accInit // Variable step: improves performance on non-compressible data.
for si < sn {
// Hash the next 4 bytes (sequence)...
match := binary.LittleEndian.Uint32(src[si:])
h := blockHash(match)
ref := hashTable[h]
hashTable[h] = si
if ref >= sn { // Invalid reference (dirty hashtable).
si++
continue
}
offset := si - ref
if offset <= 0 || offset >= winSize || // Out of window.
match != binary.LittleEndian.Uint32(src[ref:]) { // Hash collision on different matches.
// si += acc >> skipStrength
// acc++
si++
continue
}
// Match found.
// acc = accInit
lLen := si - anchor // Literal length.
// Encode match length part 1.
si += minMatch
mLen := si // Match length has minMatch already.
// Find the longest match, first looking by batches of 8 bytes.
for si < sn && binary.LittleEndian.Uint64(src[si:]) == binary.LittleEndian.Uint64(src[si-offset:]) {
si += 8
}
// Then byte by byte.
for si < sn && src[si] == src[si-offset] {
si++
}
mLen = si - mLen
if mLen < 0xF {
dst[di] = byte(mLen)
} else {
dst[di] = 0xF
}
// Encode literals length.
if lLen < 0xF {
dst[di] |= byte(lLen << 4)
} else {
dst[di] |= 0xF0
di++
l := lLen - 0xF
for ; l >= 0xFF; l -= 0xFF {
dst[di] = 0xFF
di++
}
dst[di] = byte(l)
}
di++
// Literals.
copy(dst[di:], src[anchor:anchor+lLen])
di += lLen + 2
anchor = si
// Encode offset.
_ = dst[di] // Bound check elimination.
dst[di-2], dst[di-1] = byte(offset), byte(offset>>8)
// Encode match length part 2.
if mLen >= 0xF {
for mLen -= 0xF; mLen >= 0xFF; mLen -= 0xFF {
dst[di] = 0xFF
di++
}
dst[di] = byte(mLen)
di++
}
}
if anchor == 0 {
// Incompressible.
return 0, nil
}
// Last literals.
lLen := len(src) - anchor
if lLen < 0xF {
dst[di] = byte(lLen << 4)
} else {
dst[di] = 0xF0
di++
for lLen -= 0xF; lLen >= 0xFF; lLen -= 0xFF {
dst[di] = 0xFF
di++
}
dst[di] = byte(lLen)
}
di++
// Write the last literals.
if di >= anchor {
// Incompressible.
return 0, nil
}
di += copy(dst[di:], src[anchor:])
return di, nil
}
// CompressBlockHC compresses the source buffer src into the destination dst
// with max search depth (use 0 or negative value for no max).
//
// CompressBlockHC compression ratio is better than CompressBlock but it is also slower.
//
// The size of the compressed data is returned. If it is 0 and no error, then the data is not compressible.
//
// An error is returned if the destination buffer is too small.
func CompressBlockHC(src, dst []byte, depth int) (di int, err error) {
defer func() {
if recover() != nil {
err = ErrInvalidSourceShortBuffer
}
}()
sn, dn := len(src)-mfLimit, len(dst)
if sn <= 0 || dn == 0 {
return 0, nil
}
var si int
// hashTable: stores the last position found for a given hash
// chaingTable: stores previous positions for a given hash
var hashTable, chainTable [winSize]int
if depth <= 0 {
depth = winSize
}
anchor := si
for si < sn {
// Hash the next 4 bytes (sequence).
match := binary.LittleEndian.Uint32(src[si:])
h := blockHash(match)
// Follow the chain until out of window and give the longest match.
mLen := 0
offset := 0
for next, try := hashTable[h], depth; try > 0 && next > 0 && si-next < winSize; next = chainTable[next&winMask] {
// The first (mLen==0) or next byte (mLen>=minMatch) at current match length
// must match to improve on the match length.
if src[next+mLen] != src[si+mLen] {
continue
}
ml := 0
// Compare the current position with a previous with the same hash.
for ml < sn-si && binary.LittleEndian.Uint64(src[next+ml:]) == binary.LittleEndian.Uint64(src[si+ml:]) {
ml += 8
}
for ml < sn-si && src[next+ml] == src[si+ml] {
ml++
}
if ml+1 < minMatch || ml <= mLen {
// Match too small (<minMath) or smaller than the current match.
continue
}
// Found a longer match, keep its position and length.
mLen = ml
offset = si - next
// Try another previous position with the same hash.
try--
}
chainTable[si&winMask] = hashTable[h]
hashTable[h] = si
// No match found.
if mLen == 0 {
si++
continue
}
// Match found.
// Update hash/chain tables with overlapping bytes:
// si already hashed, add everything from si+1 up to the match length.
winStart := si + 1
if ws := si + mLen - winSize; ws > winStart {
winStart = ws
}
for si, ml := winStart, si+mLen; si < ml; {
match >>= 8
match |= uint32(src[si+3]) << 24
h := blockHash(match)
chainTable[si&winMask] = hashTable[h]
hashTable[h] = si
si++
}
lLen := si - anchor
si += mLen
mLen -= minMatch // Match length does not include minMatch.
if mLen < 0xF {
dst[di] = byte(mLen)
} else {
dst[di] = 0xF
}
// Encode literals length.
if lLen < 0xF {
dst[di] |= byte(lLen << 4)
} else {
dst[di] |= 0xF0
di++
l := lLen - 0xF
for ; l >= 0xFF; l -= 0xFF {
dst[di] = 0xFF
di++
}
dst[di] = byte(l)
}
di++
// Literals.
copy(dst[di:], src[anchor:anchor+lLen])
di += lLen
anchor = si
// Encode offset.
di += 2
dst[di-2], dst[di-1] = byte(offset), byte(offset>>8)
// Encode match length part 2.
if mLen >= 0xF {
for mLen -= 0xF; mLen >= 0xFF; mLen -= 0xFF {
dst[di] = 0xFF
di++
}
dst[di] = byte(mLen)
di++
}
}
if anchor == 0 {
// Incompressible.
return 0, nil
}
// Last literals.
lLen := len(src) - anchor
if lLen < 0xF {
dst[di] = byte(lLen << 4)
} else {
dst[di] = 0xF0
di++
lLen -= 0xF
for ; lLen >= 0xFF; lLen -= 0xFF {
dst[di] = 0xFF
di++
}
dst[di] = byte(lLen)
}
di++
// Write the last literals.
if di >= anchor {
// Incompressible.
return 0, nil
}
di += copy(dst[di:], src[anchor:])
return di, nil
}