mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2024-12-05 10:02:47 +00:00
306 lines
7.4 KiB
Go
306 lines
7.4 KiB
Go
|
package flate
|
||
|
|
||
|
import (
|
||
|
"io"
|
||
|
"math"
|
||
|
"sync"
|
||
|
)
|
||
|
|
||
|
const (
|
||
|
maxStatelessBlock = math.MaxInt16
|
||
|
// dictionary will be taken from maxStatelessBlock, so limit it.
|
||
|
maxStatelessDict = 8 << 10
|
||
|
|
||
|
slTableBits = 13
|
||
|
slTableSize = 1 << slTableBits
|
||
|
slTableShift = 32 - slTableBits
|
||
|
)
|
||
|
|
||
|
type statelessWriter struct {
|
||
|
dst io.Writer
|
||
|
closed bool
|
||
|
}
|
||
|
|
||
|
func (s *statelessWriter) Close() error {
|
||
|
if s.closed {
|
||
|
return nil
|
||
|
}
|
||
|
s.closed = true
|
||
|
// Emit EOF block
|
||
|
return StatelessDeflate(s.dst, nil, true, nil)
|
||
|
}
|
||
|
|
||
|
func (s *statelessWriter) Write(p []byte) (n int, err error) {
|
||
|
err = StatelessDeflate(s.dst, p, false, nil)
|
||
|
if err != nil {
|
||
|
return 0, err
|
||
|
}
|
||
|
return len(p), nil
|
||
|
}
|
||
|
|
||
|
func (s *statelessWriter) Reset(w io.Writer) {
|
||
|
s.dst = w
|
||
|
s.closed = false
|
||
|
}
|
||
|
|
||
|
// NewStatelessWriter will do compression but without maintaining any state
|
||
|
// between Write calls.
|
||
|
// There will be no memory kept between Write calls,
|
||
|
// but compression and speed will be suboptimal.
|
||
|
// Because of this, the size of actual Write calls will affect output size.
|
||
|
func NewStatelessWriter(dst io.Writer) io.WriteCloser {
|
||
|
return &statelessWriter{dst: dst}
|
||
|
}
|
||
|
|
||
|
// bitWriterPool contains bit writers that can be reused.
|
||
|
var bitWriterPool = sync.Pool{
|
||
|
New: func() interface{} {
|
||
|
return newHuffmanBitWriter(nil)
|
||
|
},
|
||
|
}
|
||
|
|
||
|
// StatelessDeflate allows compressing directly to a Writer without retaining state.
|
||
|
// When returning everything will be flushed.
|
||
|
// Up to 8KB of an optional dictionary can be given which is presumed to precede the block.
|
||
|
// Longer dictionaries will be truncated and will still produce valid output.
|
||
|
// Sending nil dictionary is perfectly fine.
|
||
|
func StatelessDeflate(out io.Writer, in []byte, eof bool, dict []byte) error {
|
||
|
var dst tokens
|
||
|
bw := bitWriterPool.Get().(*huffmanBitWriter)
|
||
|
bw.reset(out)
|
||
|
defer func() {
|
||
|
// don't keep a reference to our output
|
||
|
bw.reset(nil)
|
||
|
bitWriterPool.Put(bw)
|
||
|
}()
|
||
|
if eof && len(in) == 0 {
|
||
|
// Just write an EOF block.
|
||
|
// Could be faster...
|
||
|
bw.writeStoredHeader(0, true)
|
||
|
bw.flush()
|
||
|
return bw.err
|
||
|
}
|
||
|
|
||
|
// Truncate dict
|
||
|
if len(dict) > maxStatelessDict {
|
||
|
dict = dict[len(dict)-maxStatelessDict:]
|
||
|
}
|
||
|
|
||
|
for len(in) > 0 {
|
||
|
todo := in
|
||
|
if len(todo) > maxStatelessBlock-len(dict) {
|
||
|
todo = todo[:maxStatelessBlock-len(dict)]
|
||
|
}
|
||
|
in = in[len(todo):]
|
||
|
uncompressed := todo
|
||
|
if len(dict) > 0 {
|
||
|
// combine dict and source
|
||
|
bufLen := len(todo) + len(dict)
|
||
|
combined := make([]byte, bufLen)
|
||
|
copy(combined, dict)
|
||
|
copy(combined[len(dict):], todo)
|
||
|
todo = combined
|
||
|
}
|
||
|
// Compress
|
||
|
statelessEnc(&dst, todo, int16(len(dict)))
|
||
|
isEof := eof && len(in) == 0
|
||
|
|
||
|
if dst.n == 0 {
|
||
|
bw.writeStoredHeader(len(uncompressed), isEof)
|
||
|
if bw.err != nil {
|
||
|
return bw.err
|
||
|
}
|
||
|
bw.writeBytes(uncompressed)
|
||
|
} else if int(dst.n) > len(uncompressed)-len(uncompressed)>>4 {
|
||
|
// If we removed less than 1/16th, huffman compress the block.
|
||
|
bw.writeBlockHuff(isEof, uncompressed, len(in) == 0)
|
||
|
} else {
|
||
|
bw.writeBlockDynamic(&dst, isEof, uncompressed, len(in) == 0)
|
||
|
}
|
||
|
if len(in) > 0 {
|
||
|
// Retain a dict if we have more
|
||
|
dict = todo[len(todo)-maxStatelessDict:]
|
||
|
dst.Reset()
|
||
|
}
|
||
|
if bw.err != nil {
|
||
|
return bw.err
|
||
|
}
|
||
|
}
|
||
|
if !eof {
|
||
|
// Align, only a stored block can do that.
|
||
|
bw.writeStoredHeader(0, false)
|
||
|
}
|
||
|
bw.flush()
|
||
|
return bw.err
|
||
|
}
|
||
|
|
||
|
func hashSL(u uint32) uint32 {
|
||
|
return (u * 0x1e35a7bd) >> slTableShift
|
||
|
}
|
||
|
|
||
|
func load3216(b []byte, i int16) uint32 {
|
||
|
// Help the compiler eliminate bounds checks on the read so it can be done in a single read.
|
||
|
b = b[i:]
|
||
|
b = b[:4]
|
||
|
return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
|
||
|
}
|
||
|
|
||
|
func load6416(b []byte, i int16) uint64 {
|
||
|
// Help the compiler eliminate bounds checks on the read so it can be done in a single read.
|
||
|
b = b[i:]
|
||
|
b = b[:8]
|
||
|
return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
|
||
|
uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
|
||
|
}
|
||
|
|
||
|
func statelessEnc(dst *tokens, src []byte, startAt int16) {
|
||
|
const (
|
||
|
inputMargin = 12 - 1
|
||
|
minNonLiteralBlockSize = 1 + 1 + inputMargin
|
||
|
)
|
||
|
|
||
|
type tableEntry struct {
|
||
|
offset int16
|
||
|
}
|
||
|
|
||
|
var table [slTableSize]tableEntry
|
||
|
|
||
|
// This check isn't in the Snappy implementation, but there, the caller
|
||
|
// instead of the callee handles this case.
|
||
|
if len(src)-int(startAt) < minNonLiteralBlockSize {
|
||
|
// We do not fill the token table.
|
||
|
// This will be picked up by caller.
|
||
|
dst.n = 0
|
||
|
return
|
||
|
}
|
||
|
// Index until startAt
|
||
|
if startAt > 0 {
|
||
|
cv := load3232(src, 0)
|
||
|
for i := int16(0); i < startAt; i++ {
|
||
|
table[hashSL(cv)] = tableEntry{offset: i}
|
||
|
cv = (cv >> 8) | (uint32(src[i+4]) << 24)
|
||
|
}
|
||
|
}
|
||
|
|
||
|
s := startAt + 1
|
||
|
nextEmit := startAt
|
||
|
// sLimit is when to stop looking for offset/length copies. The inputMargin
|
||
|
// lets us use a fast path for emitLiteral in the main loop, while we are
|
||
|
// looking for copies.
|
||
|
sLimit := int16(len(src) - inputMargin)
|
||
|
|
||
|
// nextEmit is where in src the next emitLiteral should start from.
|
||
|
cv := load3216(src, s)
|
||
|
|
||
|
for {
|
||
|
const skipLog = 5
|
||
|
const doEvery = 2
|
||
|
|
||
|
nextS := s
|
||
|
var candidate tableEntry
|
||
|
for {
|
||
|
nextHash := hashSL(cv)
|
||
|
candidate = table[nextHash]
|
||
|
nextS = s + doEvery + (s-nextEmit)>>skipLog
|
||
|
if nextS > sLimit || nextS <= 0 {
|
||
|
goto emitRemainder
|
||
|
}
|
||
|
|
||
|
now := load6416(src, nextS)
|
||
|
table[nextHash] = tableEntry{offset: s}
|
||
|
nextHash = hashSL(uint32(now))
|
||
|
|
||
|
if cv == load3216(src, candidate.offset) {
|
||
|
table[nextHash] = tableEntry{offset: nextS}
|
||
|
break
|
||
|
}
|
||
|
|
||
|
// Do one right away...
|
||
|
cv = uint32(now)
|
||
|
s = nextS
|
||
|
nextS++
|
||
|
candidate = table[nextHash]
|
||
|
now >>= 8
|
||
|
table[nextHash] = tableEntry{offset: s}
|
||
|
|
||
|
if cv == load3216(src, candidate.offset) {
|
||
|
table[nextHash] = tableEntry{offset: nextS}
|
||
|
break
|
||
|
}
|
||
|
cv = uint32(now)
|
||
|
s = nextS
|
||
|
}
|
||
|
|
||
|
// A 4-byte match has been found. We'll later see if more than 4 bytes
|
||
|
// match. But, prior to the match, src[nextEmit:s] are unmatched. Emit
|
||
|
// them as literal bytes.
|
||
|
for {
|
||
|
// Invariant: we have a 4-byte match at s, and no need to emit any
|
||
|
// literal bytes prior to s.
|
||
|
|
||
|
// Extend the 4-byte match as long as possible.
|
||
|
t := candidate.offset
|
||
|
l := int16(matchLen(src[s+4:], src[t+4:]) + 4)
|
||
|
|
||
|
// Extend backwards
|
||
|
for t > 0 && s > nextEmit && src[t-1] == src[s-1] {
|
||
|
s--
|
||
|
t--
|
||
|
l++
|
||
|
}
|
||
|
if nextEmit < s {
|
||
|
if false {
|
||
|
emitLiteral(dst, src[nextEmit:s])
|
||
|
} else {
|
||
|
for _, v := range src[nextEmit:s] {
|
||
|
dst.tokens[dst.n] = token(v)
|
||
|
dst.litHist[v]++
|
||
|
dst.n++
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
|
||
|
// Save the match found
|
||
|
dst.AddMatchLong(int32(l), uint32(s-t-baseMatchOffset))
|
||
|
s += l
|
||
|
nextEmit = s
|
||
|
if nextS >= s {
|
||
|
s = nextS + 1
|
||
|
}
|
||
|
if s >= sLimit {
|
||
|
goto emitRemainder
|
||
|
}
|
||
|
|
||
|
// We could immediately start working at s now, but to improve
|
||
|
// compression we first update the hash table at s-2 and at s. If
|
||
|
// another emitCopy is not our next move, also calculate nextHash
|
||
|
// at s+1. At least on GOARCH=amd64, these three hash calculations
|
||
|
// are faster as one load64 call (with some shifts) instead of
|
||
|
// three load32 calls.
|
||
|
x := load6416(src, s-2)
|
||
|
o := s - 2
|
||
|
prevHash := hashSL(uint32(x))
|
||
|
table[prevHash] = tableEntry{offset: o}
|
||
|
x >>= 16
|
||
|
currHash := hashSL(uint32(x))
|
||
|
candidate = table[currHash]
|
||
|
table[currHash] = tableEntry{offset: o + 2}
|
||
|
|
||
|
if uint32(x) != load3216(src, candidate.offset) {
|
||
|
cv = uint32(x >> 8)
|
||
|
s++
|
||
|
break
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
|
||
|
emitRemainder:
|
||
|
if int(nextEmit) < len(src) {
|
||
|
// If nothing was added, don't encode literals.
|
||
|
if dst.n == 0 {
|
||
|
return
|
||
|
}
|
||
|
emitLiteral(dst, src[nextEmit:])
|
||
|
}
|
||
|
}
|