forked from mirrors/gotosocial
331 lines
8.9 KiB
Go
331 lines
8.9 KiB
Go
// Copyright (c) 2022+ Klaus Post. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package s2
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import (
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"bytes"
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"encoding/binary"
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"sync"
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)
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const (
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// MinDictSize is the minimum dictionary size when repeat has been read.
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MinDictSize = 16
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// MaxDictSize is the maximum dictionary size when repeat has been read.
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MaxDictSize = 65536
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// MaxDictSrcOffset is the maximum offset where a dictionary entry can start.
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MaxDictSrcOffset = 65535
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)
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// Dict contains a dictionary that can be used for encoding and decoding s2
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type Dict struct {
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dict []byte
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repeat int // Repeat as index of dict
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fast, better, best sync.Once
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fastTable *[1 << 14]uint16
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betterTableShort *[1 << 14]uint16
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betterTableLong *[1 << 17]uint16
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bestTableShort *[1 << 16]uint32
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bestTableLong *[1 << 19]uint32
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}
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// NewDict will read a dictionary.
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// It will return nil if the dictionary is invalid.
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func NewDict(dict []byte) *Dict {
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if len(dict) == 0 {
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return nil
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}
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var d Dict
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// Repeat is the first value of the dict
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r, n := binary.Uvarint(dict)
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if n <= 0 {
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return nil
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}
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dict = dict[n:]
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d.dict = dict
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if cap(d.dict) < len(d.dict)+16 {
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d.dict = append(make([]byte, 0, len(d.dict)+16), d.dict...)
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}
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if len(dict) < MinDictSize || len(dict) > MaxDictSize {
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return nil
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}
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d.repeat = int(r)
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if d.repeat > len(dict) {
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return nil
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}
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return &d
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}
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// Bytes will return a serialized version of the dictionary.
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// The output can be sent to NewDict.
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func (d *Dict) Bytes() []byte {
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dst := make([]byte, binary.MaxVarintLen16+len(d.dict))
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return append(dst[:binary.PutUvarint(dst, uint64(d.repeat))], d.dict...)
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}
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// MakeDict will create a dictionary.
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// 'data' must be at least MinDictSize.
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// If data is longer than MaxDictSize only the last MaxDictSize bytes will be used.
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// If searchStart is set the start repeat value will be set to the last
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// match of this content.
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// If no matches are found, it will attempt to find shorter matches.
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// This content should match the typical start of a block.
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// If at least 4 bytes cannot be matched, repeat is set to start of block.
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func MakeDict(data []byte, searchStart []byte) *Dict {
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if len(data) == 0 {
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return nil
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}
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if len(data) > MaxDictSize {
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data = data[len(data)-MaxDictSize:]
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}
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var d Dict
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dict := data
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d.dict = dict
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if cap(d.dict) < len(d.dict)+16 {
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d.dict = append(make([]byte, 0, len(d.dict)+16), d.dict...)
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}
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if len(dict) < MinDictSize {
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return nil
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}
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// Find the longest match possible, last entry if multiple.
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for s := len(searchStart); s > 4; s-- {
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if idx := bytes.LastIndex(data, searchStart[:s]); idx >= 0 && idx <= len(data)-8 {
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d.repeat = idx
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break
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}
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}
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return &d
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}
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// Encode returns the encoded form of src. The returned slice may be a sub-
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// slice of dst if dst was large enough to hold the entire encoded block.
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// Otherwise, a newly allocated slice will be returned.
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//
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// The dst and src must not overlap. It is valid to pass a nil dst.
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//
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// The blocks will require the same amount of memory to decode as encoding,
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// and does not make for concurrent decoding.
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// Also note that blocks do not contain CRC information, so corruption may be undetected.
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//
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// If you need to encode larger amounts of data, consider using
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// the streaming interface which gives all of these features.
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func (d *Dict) Encode(dst, src []byte) []byte {
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if n := MaxEncodedLen(len(src)); n < 0 {
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panic(ErrTooLarge)
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} else if cap(dst) < n {
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dst = make([]byte, n)
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} else {
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dst = dst[:n]
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}
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// The block starts with the varint-encoded length of the decompressed bytes.
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dstP := binary.PutUvarint(dst, uint64(len(src)))
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if len(src) == 0 {
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return dst[:dstP]
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}
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if len(src) < minNonLiteralBlockSize {
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dstP += emitLiteral(dst[dstP:], src)
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return dst[:dstP]
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}
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n := encodeBlockDictGo(dst[dstP:], src, d)
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if n > 0 {
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dstP += n
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return dst[:dstP]
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}
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// Not compressible
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dstP += emitLiteral(dst[dstP:], src)
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return dst[:dstP]
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}
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// EncodeBetter returns the encoded form of src. The returned slice may be a sub-
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// slice of dst if dst was large enough to hold the entire encoded block.
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// Otherwise, a newly allocated slice will be returned.
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//
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// EncodeBetter compresses better than Encode but typically with a
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// 10-40% speed decrease on both compression and decompression.
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//
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// The dst and src must not overlap. It is valid to pass a nil dst.
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//
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// The blocks will require the same amount of memory to decode as encoding,
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// and does not make for concurrent decoding.
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// Also note that blocks do not contain CRC information, so corruption may be undetected.
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//
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// If you need to encode larger amounts of data, consider using
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// the streaming interface which gives all of these features.
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func (d *Dict) EncodeBetter(dst, src []byte) []byte {
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if n := MaxEncodedLen(len(src)); n < 0 {
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panic(ErrTooLarge)
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} else if len(dst) < n {
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dst = make([]byte, n)
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}
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// The block starts with the varint-encoded length of the decompressed bytes.
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dstP := binary.PutUvarint(dst, uint64(len(src)))
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if len(src) == 0 {
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return dst[:dstP]
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}
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if len(src) < minNonLiteralBlockSize {
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dstP += emitLiteral(dst[dstP:], src)
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return dst[:dstP]
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}
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n := encodeBlockBetterDict(dst[dstP:], src, d)
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if n > 0 {
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dstP += n
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return dst[:dstP]
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}
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// Not compressible
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dstP += emitLiteral(dst[dstP:], src)
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return dst[:dstP]
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}
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// EncodeBest returns the encoded form of src. The returned slice may be a sub-
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// slice of dst if dst was large enough to hold the entire encoded block.
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// Otherwise, a newly allocated slice will be returned.
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//
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// EncodeBest compresses as good as reasonably possible but with a
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// big speed decrease.
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//
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// The dst and src must not overlap. It is valid to pass a nil dst.
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//
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// The blocks will require the same amount of memory to decode as encoding,
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// and does not make for concurrent decoding.
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// Also note that blocks do not contain CRC information, so corruption may be undetected.
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//
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// If you need to encode larger amounts of data, consider using
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// the streaming interface which gives all of these features.
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func (d *Dict) EncodeBest(dst, src []byte) []byte {
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if n := MaxEncodedLen(len(src)); n < 0 {
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panic(ErrTooLarge)
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} else if len(dst) < n {
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dst = make([]byte, n)
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}
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// The block starts with the varint-encoded length of the decompressed bytes.
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dstP := binary.PutUvarint(dst, uint64(len(src)))
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if len(src) == 0 {
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return dst[:dstP]
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}
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if len(src) < minNonLiteralBlockSize {
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dstP += emitLiteral(dst[dstP:], src)
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return dst[:dstP]
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}
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n := encodeBlockBest(dst[dstP:], src, d)
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if n > 0 {
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dstP += n
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return dst[:dstP]
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}
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// Not compressible
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dstP += emitLiteral(dst[dstP:], src)
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return dst[:dstP]
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}
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// Decode returns the decoded form of src. The returned slice may be a sub-
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// slice of dst if dst was large enough to hold the entire decoded block.
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// Otherwise, a newly allocated slice will be returned.
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//
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// The dst and src must not overlap. It is valid to pass a nil dst.
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func (d *Dict) Decode(dst, src []byte) ([]byte, error) {
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dLen, s, err := decodedLen(src)
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if err != nil {
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return nil, err
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}
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if dLen <= cap(dst) {
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dst = dst[:dLen]
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} else {
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dst = make([]byte, dLen)
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}
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if s2DecodeDict(dst, src[s:], d) != 0 {
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return nil, ErrCorrupt
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}
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return dst, nil
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}
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func (d *Dict) initFast() {
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d.fast.Do(func() {
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const (
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tableBits = 14
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maxTableSize = 1 << tableBits
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)
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var table [maxTableSize]uint16
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// We stop so any entry of length 8 can always be read.
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for i := 0; i < len(d.dict)-8-2; i += 3 {
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x0 := load64(d.dict, i)
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h0 := hash6(x0, tableBits)
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h1 := hash6(x0>>8, tableBits)
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h2 := hash6(x0>>16, tableBits)
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table[h0] = uint16(i)
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table[h1] = uint16(i + 1)
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table[h2] = uint16(i + 2)
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}
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d.fastTable = &table
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})
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}
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func (d *Dict) initBetter() {
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d.better.Do(func() {
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const (
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// Long hash matches.
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lTableBits = 17
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maxLTableSize = 1 << lTableBits
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// Short hash matches.
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sTableBits = 14
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maxSTableSize = 1 << sTableBits
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)
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var lTable [maxLTableSize]uint16
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var sTable [maxSTableSize]uint16
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// We stop so any entry of length 8 can always be read.
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for i := 0; i < len(d.dict)-8; i++ {
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cv := load64(d.dict, i)
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lTable[hash7(cv, lTableBits)] = uint16(i)
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sTable[hash4(cv, sTableBits)] = uint16(i)
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}
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d.betterTableShort = &sTable
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d.betterTableLong = &lTable
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})
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}
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func (d *Dict) initBest() {
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d.best.Do(func() {
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const (
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// Long hash matches.
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lTableBits = 19
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maxLTableSize = 1 << lTableBits
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// Short hash matches.
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sTableBits = 16
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maxSTableSize = 1 << sTableBits
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)
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var lTable [maxLTableSize]uint32
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var sTable [maxSTableSize]uint32
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// We stop so any entry of length 8 can always be read.
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for i := 0; i < len(d.dict)-8; i++ {
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cv := load64(d.dict, i)
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hashL := hash8(cv, lTableBits)
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hashS := hash4(cv, sTableBits)
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candidateL := lTable[hashL]
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candidateS := sTable[hashS]
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lTable[hashL] = uint32(i) | candidateL<<16
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sTable[hashS] = uint32(i) | candidateS<<16
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}
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d.bestTableShort = &sTable
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d.bestTableLong = &lTable
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})
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}
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