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535 lines
12 KiB
Go
535 lines
12 KiB
Go
package zstd
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import (
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"bytes"
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"encoding/binary"
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"errors"
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"fmt"
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"io"
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"math"
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"sort"
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"github.com/klauspost/compress/huff0"
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)
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type dict struct {
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id uint32
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litEnc *huff0.Scratch
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llDec, ofDec, mlDec sequenceDec
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offsets [3]int
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content []byte
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}
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const dictMagic = "\x37\xa4\x30\xec"
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// Maximum dictionary size for the reference implementation (1.5.3) is 2 GiB.
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const dictMaxLength = 1 << 31
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// ID returns the dictionary id or 0 if d is nil.
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func (d *dict) ID() uint32 {
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if d == nil {
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return 0
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}
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return d.id
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}
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// ContentSize returns the dictionary content size or 0 if d is nil.
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func (d *dict) ContentSize() int {
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if d == nil {
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return 0
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}
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return len(d.content)
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}
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// Content returns the dictionary content.
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func (d *dict) Content() []byte {
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if d == nil {
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return nil
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}
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return d.content
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}
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// Offsets returns the initial offsets.
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func (d *dict) Offsets() [3]int {
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if d == nil {
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return [3]int{}
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}
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return d.offsets
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}
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// LitEncoder returns the literal encoder.
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func (d *dict) LitEncoder() *huff0.Scratch {
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if d == nil {
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return nil
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}
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return d.litEnc
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}
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// Load a dictionary as described in
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// https://github.com/facebook/zstd/blob/master/doc/zstd_compression_format.md#dictionary-format
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func loadDict(b []byte) (*dict, error) {
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// Check static field size.
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if len(b) <= 8+(3*4) {
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return nil, io.ErrUnexpectedEOF
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}
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d := dict{
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llDec: sequenceDec{fse: &fseDecoder{}},
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ofDec: sequenceDec{fse: &fseDecoder{}},
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mlDec: sequenceDec{fse: &fseDecoder{}},
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}
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if string(b[:4]) != dictMagic {
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return nil, ErrMagicMismatch
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}
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d.id = binary.LittleEndian.Uint32(b[4:8])
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if d.id == 0 {
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return nil, errors.New("dictionaries cannot have ID 0")
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}
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// Read literal table
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var err error
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d.litEnc, b, err = huff0.ReadTable(b[8:], nil)
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if err != nil {
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return nil, fmt.Errorf("loading literal table: %w", err)
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}
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d.litEnc.Reuse = huff0.ReusePolicyMust
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br := byteReader{
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b: b,
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off: 0,
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}
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readDec := func(i tableIndex, dec *fseDecoder) error {
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if err := dec.readNCount(&br, uint16(maxTableSymbol[i])); err != nil {
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return err
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}
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if br.overread() {
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return io.ErrUnexpectedEOF
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}
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err = dec.transform(symbolTableX[i])
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if err != nil {
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println("Transform table error:", err)
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return err
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}
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if debugDecoder || debugEncoder {
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println("Read table ok", "symbolLen:", dec.symbolLen)
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}
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// Set decoders as predefined so they aren't reused.
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dec.preDefined = true
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return nil
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}
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if err := readDec(tableOffsets, d.ofDec.fse); err != nil {
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return nil, err
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}
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if err := readDec(tableMatchLengths, d.mlDec.fse); err != nil {
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return nil, err
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}
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if err := readDec(tableLiteralLengths, d.llDec.fse); err != nil {
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return nil, err
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}
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if br.remain() < 12 {
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return nil, io.ErrUnexpectedEOF
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}
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d.offsets[0] = int(br.Uint32())
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br.advance(4)
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d.offsets[1] = int(br.Uint32())
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br.advance(4)
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d.offsets[2] = int(br.Uint32())
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br.advance(4)
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if d.offsets[0] <= 0 || d.offsets[1] <= 0 || d.offsets[2] <= 0 {
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return nil, errors.New("invalid offset in dictionary")
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}
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d.content = make([]byte, br.remain())
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copy(d.content, br.unread())
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if d.offsets[0] > len(d.content) || d.offsets[1] > len(d.content) || d.offsets[2] > len(d.content) {
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return nil, fmt.Errorf("initial offset bigger than dictionary content size %d, offsets: %v", len(d.content), d.offsets)
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}
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return &d, nil
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}
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// InspectDictionary loads a zstd dictionary and provides functions to inspect the content.
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func InspectDictionary(b []byte) (interface {
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ID() uint32
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ContentSize() int
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Content() []byte
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Offsets() [3]int
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LitEncoder() *huff0.Scratch
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}, error) {
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initPredefined()
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d, err := loadDict(b)
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return d, err
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}
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type BuildDictOptions struct {
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// Dictionary ID.
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ID uint32
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// Content to use to create dictionary tables.
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Contents [][]byte
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// History to use for all blocks.
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History []byte
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// Offsets to use.
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Offsets [3]int
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// CompatV155 will make the dictionary compatible with Zstd v1.5.5 and earlier.
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// See https://github.com/facebook/zstd/issues/3724
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CompatV155 bool
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// Use the specified encoder level.
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// The dictionary will be built using the specified encoder level,
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// which will reflect speed and make the dictionary tailored for that level.
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// If not set SpeedBestCompression will be used.
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Level EncoderLevel
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// DebugOut will write stats and other details here if set.
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DebugOut io.Writer
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}
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func BuildDict(o BuildDictOptions) ([]byte, error) {
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initPredefined()
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hist := o.History
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contents := o.Contents
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debug := o.DebugOut != nil
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println := func(args ...interface{}) {
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if o.DebugOut != nil {
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fmt.Fprintln(o.DebugOut, args...)
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}
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}
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printf := func(s string, args ...interface{}) {
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if o.DebugOut != nil {
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fmt.Fprintf(o.DebugOut, s, args...)
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}
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}
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print := func(args ...interface{}) {
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if o.DebugOut != nil {
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fmt.Fprint(o.DebugOut, args...)
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}
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}
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if int64(len(hist)) > dictMaxLength {
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return nil, fmt.Errorf("dictionary of size %d > %d", len(hist), int64(dictMaxLength))
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}
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if len(hist) < 8 {
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return nil, fmt.Errorf("dictionary of size %d < %d", len(hist), 8)
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}
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if len(contents) == 0 {
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return nil, errors.New("no content provided")
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}
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d := dict{
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id: o.ID,
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litEnc: nil,
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llDec: sequenceDec{},
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ofDec: sequenceDec{},
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mlDec: sequenceDec{},
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offsets: o.Offsets,
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content: hist,
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}
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block := blockEnc{lowMem: false}
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block.init()
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enc := encoder(&bestFastEncoder{fastBase: fastBase{maxMatchOff: int32(maxMatchLen), bufferReset: math.MaxInt32 - int32(maxMatchLen*2), lowMem: false}})
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if o.Level != 0 {
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eOpts := encoderOptions{
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level: o.Level,
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blockSize: maxMatchLen,
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windowSize: maxMatchLen,
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dict: &d,
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lowMem: false,
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}
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enc = eOpts.encoder()
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} else {
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o.Level = SpeedBestCompression
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}
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var (
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remain [256]int
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ll [256]int
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ml [256]int
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of [256]int
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)
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addValues := func(dst *[256]int, src []byte) {
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for _, v := range src {
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dst[v]++
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}
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}
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addHist := func(dst *[256]int, src *[256]uint32) {
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for i, v := range src {
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dst[i] += int(v)
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}
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}
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seqs := 0
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nUsed := 0
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litTotal := 0
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newOffsets := make(map[uint32]int, 1000)
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for _, b := range contents {
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block.reset(nil)
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if len(b) < 8 {
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continue
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}
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nUsed++
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enc.Reset(&d, true)
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enc.Encode(&block, b)
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addValues(&remain, block.literals)
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litTotal += len(block.literals)
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seqs += len(block.sequences)
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block.genCodes()
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addHist(&ll, block.coders.llEnc.Histogram())
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addHist(&ml, block.coders.mlEnc.Histogram())
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addHist(&of, block.coders.ofEnc.Histogram())
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for i, seq := range block.sequences {
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if i > 3 {
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break
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}
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offset := seq.offset
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if offset == 0 {
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continue
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}
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if offset > 3 {
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newOffsets[offset-3]++
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} else {
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newOffsets[uint32(o.Offsets[offset-1])]++
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}
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}
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}
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// Find most used offsets.
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var sortedOffsets []uint32
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for k := range newOffsets {
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sortedOffsets = append(sortedOffsets, k)
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}
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sort.Slice(sortedOffsets, func(i, j int) bool {
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a, b := sortedOffsets[i], sortedOffsets[j]
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if a == b {
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// Prefer the longer offset
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return sortedOffsets[i] > sortedOffsets[j]
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}
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return newOffsets[sortedOffsets[i]] > newOffsets[sortedOffsets[j]]
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})
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if len(sortedOffsets) > 3 {
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if debug {
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print("Offsets:")
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for i, v := range sortedOffsets {
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if i > 20 {
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break
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}
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printf("[%d: %d],", v, newOffsets[v])
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}
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println("")
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}
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sortedOffsets = sortedOffsets[:3]
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}
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for i, v := range sortedOffsets {
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o.Offsets[i] = int(v)
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}
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if debug {
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println("New repeat offsets", o.Offsets)
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}
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if nUsed == 0 || seqs == 0 {
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return nil, fmt.Errorf("%d blocks, %d sequences found", nUsed, seqs)
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}
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if debug {
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println("Sequences:", seqs, "Blocks:", nUsed, "Literals:", litTotal)
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}
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if seqs/nUsed < 512 {
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// Use 512 as minimum.
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nUsed = seqs / 512
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}
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copyHist := func(dst *fseEncoder, src *[256]int) ([]byte, error) {
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hist := dst.Histogram()
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var maxSym uint8
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var maxCount int
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var fakeLength int
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for i, v := range src {
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if v > 0 {
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v = v / nUsed
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if v == 0 {
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v = 1
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}
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}
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if v > maxCount {
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maxCount = v
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}
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if v != 0 {
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maxSym = uint8(i)
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}
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fakeLength += v
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hist[i] = uint32(v)
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}
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dst.HistogramFinished(maxSym, maxCount)
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dst.reUsed = false
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dst.useRLE = false
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err := dst.normalizeCount(fakeLength)
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if err != nil {
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return nil, err
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}
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if debug {
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println("RAW:", dst.count[:maxSym+1], "NORM:", dst.norm[:maxSym+1], "LEN:", fakeLength)
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}
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return dst.writeCount(nil)
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}
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if debug {
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print("Literal lengths: ")
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}
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llTable, err := copyHist(block.coders.llEnc, &ll)
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if err != nil {
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return nil, err
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}
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if debug {
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print("Match lengths: ")
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}
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mlTable, err := copyHist(block.coders.mlEnc, &ml)
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if err != nil {
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return nil, err
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}
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if debug {
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print("Offsets: ")
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}
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ofTable, err := copyHist(block.coders.ofEnc, &of)
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if err != nil {
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return nil, err
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}
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// Literal table
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avgSize := litTotal
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if avgSize > huff0.BlockSizeMax/2 {
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avgSize = huff0.BlockSizeMax / 2
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}
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huffBuff := make([]byte, 0, avgSize)
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// Target size
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div := litTotal / avgSize
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if div < 1 {
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div = 1
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}
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if debug {
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println("Huffman weights:")
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}
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for i, n := range remain[:] {
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if n > 0 {
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n = n / div
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// Allow all entries to be represented.
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if n == 0 {
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n = 1
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}
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huffBuff = append(huffBuff, bytes.Repeat([]byte{byte(i)}, n)...)
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if debug {
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printf("[%d: %d], ", i, n)
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}
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}
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}
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if o.CompatV155 && remain[255]/div == 0 {
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huffBuff = append(huffBuff, 255)
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}
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scratch := &huff0.Scratch{TableLog: 11}
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for tries := 0; tries < 255; tries++ {
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scratch = &huff0.Scratch{TableLog: 11}
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_, _, err = huff0.Compress1X(huffBuff, scratch)
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if err == nil {
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break
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}
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if debug {
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printf("Try %d: Huffman error: %v\n", tries+1, err)
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}
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huffBuff = huffBuff[:0]
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if tries == 250 {
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if debug {
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println("Huffman: Bailing out with predefined table")
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}
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// Bail out.... Just generate something
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huffBuff = append(huffBuff, bytes.Repeat([]byte{255}, 10000)...)
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for i := 0; i < 128; i++ {
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huffBuff = append(huffBuff, byte(i))
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}
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continue
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}
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if errors.Is(err, huff0.ErrIncompressible) {
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// Try truncating least common.
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for i, n := range remain[:] {
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if n > 0 {
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n = n / (div * (i + 1))
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if n > 0 {
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huffBuff = append(huffBuff, bytes.Repeat([]byte{byte(i)}, n)...)
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}
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}
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}
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if o.CompatV155 && len(huffBuff) > 0 && huffBuff[len(huffBuff)-1] != 255 {
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huffBuff = append(huffBuff, 255)
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}
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if len(huffBuff) == 0 {
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huffBuff = append(huffBuff, 0, 255)
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}
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}
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if errors.Is(err, huff0.ErrUseRLE) {
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for i, n := range remain[:] {
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n = n / (div * (i + 1))
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// Allow all entries to be represented.
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if n == 0 {
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n = 1
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}
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huffBuff = append(huffBuff, bytes.Repeat([]byte{byte(i)}, n)...)
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}
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}
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}
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var out bytes.Buffer
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out.Write([]byte(dictMagic))
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out.Write(binary.LittleEndian.AppendUint32(nil, o.ID))
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out.Write(scratch.OutTable)
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if debug {
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println("huff table:", len(scratch.OutTable), "bytes")
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println("of table:", len(ofTable), "bytes")
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println("ml table:", len(mlTable), "bytes")
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println("ll table:", len(llTable), "bytes")
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}
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out.Write(ofTable)
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out.Write(mlTable)
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out.Write(llTable)
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out.Write(binary.LittleEndian.AppendUint32(nil, uint32(o.Offsets[0])))
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out.Write(binary.LittleEndian.AppendUint32(nil, uint32(o.Offsets[1])))
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out.Write(binary.LittleEndian.AppendUint32(nil, uint32(o.Offsets[2])))
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out.Write(hist)
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if debug {
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_, err := loadDict(out.Bytes())
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if err != nil {
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panic(err)
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}
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i, err := InspectDictionary(out.Bytes())
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if err != nil {
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panic(err)
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}
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println("ID:", i.ID())
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println("Content size:", i.ContentSize())
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println("Encoder:", i.LitEncoder() != nil)
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println("Offsets:", i.Offsets())
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var totalSize int
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for _, b := range contents {
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totalSize += len(b)
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}
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encWith := func(opts ...EOption) int {
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enc, err := NewWriter(nil, opts...)
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if err != nil {
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panic(err)
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}
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defer enc.Close()
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var dst []byte
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var totalSize int
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for _, b := range contents {
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dst = enc.EncodeAll(b, dst[:0])
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totalSize += len(dst)
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}
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return totalSize
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}
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plain := encWith(WithEncoderLevel(o.Level))
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withDict := encWith(WithEncoderLevel(o.Level), WithEncoderDict(out.Bytes()))
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println("Input size:", totalSize)
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println("Plain Compressed:", plain)
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println("Dict Compressed:", withDict)
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println("Saved:", plain-withDict, (plain-withDict)/len(contents), "bytes per input (rounded down)")
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}
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return out.Bytes(), nil
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}
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