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