388 lines
9.6 KiB
Go
388 lines
9.6 KiB
Go
package lz4
|
|
|
|
import (
|
|
"encoding/binary"
|
|
"fmt"
|
|
"math/bits"
|
|
)
|
|
|
|
// blockHash hashes the lower 6 bytes into a value < htSize.
|
|
func blockHash(x uint64) uint32 {
|
|
const prime6bytes = 227718039650203
|
|
return uint32(((x << (64 - 48)) * prime6bytes) >> (64 - hashLog))
|
|
}
|
|
|
|
// 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) (int, error) {
|
|
if len(src) == 0 {
|
|
return 0, nil
|
|
}
|
|
if di := decodeBlock(dst, src); di >= 0 {
|
|
return di, nil
|
|
}
|
|
return 0, ErrInvalidSourceShortBuffer
|
|
}
|
|
|
|
// 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 recoverBlock(&err)
|
|
|
|
// 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 compresssion.
|
|
// bytes to skip = 1 + (bytes since last match >> adaptSkipLog)
|
|
const adaptSkipLog = 7
|
|
sn, dn := len(src)-mfLimit, len(dst)
|
|
if sn <= 0 || dn == 0 {
|
|
return 0, nil
|
|
}
|
|
if len(hashTable) < htSize {
|
|
return 0, fmt.Errorf("hash table too small, should be at least %d in size", htSize)
|
|
}
|
|
// Prove to the compiler the table has at least htSize elements.
|
|
// The compiler can see that "uint32() >> hashShift" cannot be out of bounds.
|
|
hashTable = hashTable[:htSize]
|
|
|
|
// si: Current position of the search.
|
|
// anchor: Position of the current literals.
|
|
var si, anchor int
|
|
|
|
// Fast scan strategy: the hash table only stores the last 4 bytes sequences.
|
|
for si < sn {
|
|
// Hash the next 6 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 := hashTable[h]
|
|
ref2 := hashTable[h2]
|
|
hashTable[h] = si
|
|
hashTable[h2] = si + 1
|
|
offset := si - ref
|
|
|
|
// If offset <= 0 we got an old entry in the hash table.
|
|
if offset <= 0 || offset >= winSize || // Out of window.
|
|
uint32(match) != binary.LittleEndian.Uint32(src[ref:]) { // Hash collision on different matches.
|
|
// No match. Start calculating another hash.
|
|
// The processor can usually do this out-of-order.
|
|
h = blockHash(match >> 16)
|
|
ref = hashTable[h]
|
|
|
|
// 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 - ref
|
|
hashTable[h] = si
|
|
|
|
if offset <= 0 || offset >= winSize ||
|
|
uint32(match>>16) != binary.LittleEndian.Uint32(src[ref:]) {
|
|
// 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 < 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 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:di+lLen], 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++
|
|
}
|
|
// Check if we can load next values.
|
|
if si >= sn {
|
|
break
|
|
}
|
|
// Hash match end-2
|
|
h = blockHash(binary.LittleEndian.Uint64(src[si-2:]))
|
|
hashTable[h] = si - 2
|
|
}
|
|
|
|
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:di+len(src)-anchor], src[anchor:])
|
|
return di, nil
|
|
}
|
|
|
|
// blockHash hashes 4 bytes into a value < winSize.
|
|
func blockHashHC(x uint32) uint32 {
|
|
const hasher uint32 = 2654435761 // Knuth multiplicative hash.
|
|
return x * hasher >> (32 - winSizeLog)
|
|
}
|
|
|
|
// 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 recoverBlock(&err)
|
|
|
|
// 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 compresssion.
|
|
// bytes to skip = 1 + (bytes since last match >> adaptSkipLog)
|
|
const adaptSkipLog = 7
|
|
|
|
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
|
|
// chainTable: 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 := blockHashHC(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 {
|
|
x := binary.LittleEndian.Uint64(src[next+ml:]) ^ binary.LittleEndian.Uint64(src[si+ml:])
|
|
if x == 0 {
|
|
ml += 8
|
|
} else {
|
|
// Stop is first non-zero byte.
|
|
ml += bits.TrailingZeros64(x) >> 3
|
|
break
|
|
}
|
|
}
|
|
if ml < 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 += 1 + (si-anchor)>>adaptSkipLog
|
|
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 := blockHashHC(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:di+lLen], 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:di+len(src)-anchor], src[anchor:])
|
|
return di, nil
|
|
}
|