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684 lines
17 KiB
684 lines
17 KiB
// Copyright 2018 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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// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
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package fse
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import (
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"errors"
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"fmt"
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)
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// Compress the input bytes. Input must be < 2GB.
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// Provide a Scratch buffer to avoid memory allocations.
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// Note that the output is also kept in the scratch buffer.
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// If input is too hard to compress, ErrIncompressible is returned.
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// If input is a single byte value repeated ErrUseRLE is returned.
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func Compress(in []byte, s *Scratch) ([]byte, error) {
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if len(in) <= 1 {
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return nil, ErrIncompressible
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}
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if len(in) > (2<<30)-1 {
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return nil, errors.New("input too big, must be < 2GB")
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}
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s, err := s.prepare(in)
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if err != nil {
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return nil, err
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}
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// Create histogram, if none was provided.
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maxCount := s.maxCount
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if maxCount == 0 {
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maxCount = s.countSimple(in)
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}
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// Reset for next run.
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s.clearCount = true
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s.maxCount = 0
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if maxCount == len(in) {
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// One symbol, use RLE
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return nil, ErrUseRLE
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}
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if maxCount == 1 || maxCount < (len(in)>>7) {
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// Each symbol present maximum once or too well distributed.
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return nil, ErrIncompressible
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}
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s.optimalTableLog()
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err = s.normalizeCount()
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if err != nil {
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return nil, err
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}
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err = s.writeCount()
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if err != nil {
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return nil, err
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}
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if false {
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err = s.validateNorm()
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if err != nil {
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return nil, err
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}
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}
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err = s.buildCTable()
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if err != nil {
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return nil, err
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}
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err = s.compress(in)
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if err != nil {
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return nil, err
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}
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s.Out = s.bw.out
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// Check if we compressed.
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if len(s.Out) >= len(in) {
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return nil, ErrIncompressible
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}
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return s.Out, nil
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}
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// cState contains the compression state of a stream.
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type cState struct {
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bw *bitWriter
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stateTable []uint16
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state uint16
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}
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// init will initialize the compression state to the first symbol of the stream.
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func (c *cState) init(bw *bitWriter, ct *cTable, tableLog uint8, first symbolTransform) {
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c.bw = bw
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c.stateTable = ct.stateTable
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nbBitsOut := (first.deltaNbBits + (1 << 15)) >> 16
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im := int32((nbBitsOut << 16) - first.deltaNbBits)
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lu := (im >> nbBitsOut) + first.deltaFindState
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c.state = c.stateTable[lu]
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return
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}
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// encode the output symbol provided and write it to the bitstream.
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func (c *cState) encode(symbolTT symbolTransform) {
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nbBitsOut := (uint32(c.state) + symbolTT.deltaNbBits) >> 16
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dstState := int32(c.state>>(nbBitsOut&15)) + symbolTT.deltaFindState
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c.bw.addBits16NC(c.state, uint8(nbBitsOut))
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c.state = c.stateTable[dstState]
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}
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// encode the output symbol provided and write it to the bitstream.
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func (c *cState) encodeZero(symbolTT symbolTransform) {
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nbBitsOut := (uint32(c.state) + symbolTT.deltaNbBits) >> 16
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dstState := int32(c.state>>(nbBitsOut&15)) + symbolTT.deltaFindState
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c.bw.addBits16ZeroNC(c.state, uint8(nbBitsOut))
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c.state = c.stateTable[dstState]
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}
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// flush will write the tablelog to the output and flush the remaining full bytes.
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func (c *cState) flush(tableLog uint8) {
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c.bw.flush32()
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c.bw.addBits16NC(c.state, tableLog)
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c.bw.flush()
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}
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// compress is the main compression loop that will encode the input from the last byte to the first.
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func (s *Scratch) compress(src []byte) error {
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if len(src) <= 2 {
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return errors.New("compress: src too small")
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}
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tt := s.ct.symbolTT[:256]
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s.bw.reset(s.Out)
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// Our two states each encodes every second byte.
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// Last byte encoded (first byte decoded) will always be encoded by c1.
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var c1, c2 cState
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// Encode so remaining size is divisible by 4.
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ip := len(src)
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if ip&1 == 1 {
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c1.init(&s.bw, &s.ct, s.actualTableLog, tt[src[ip-1]])
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c2.init(&s.bw, &s.ct, s.actualTableLog, tt[src[ip-2]])
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c1.encodeZero(tt[src[ip-3]])
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ip -= 3
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} else {
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c2.init(&s.bw, &s.ct, s.actualTableLog, tt[src[ip-1]])
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c1.init(&s.bw, &s.ct, s.actualTableLog, tt[src[ip-2]])
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ip -= 2
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}
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if ip&2 != 0 {
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c2.encodeZero(tt[src[ip-1]])
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c1.encodeZero(tt[src[ip-2]])
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ip -= 2
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}
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// Main compression loop.
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switch {
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case !s.zeroBits && s.actualTableLog <= 8:
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// We can encode 4 symbols without requiring a flush.
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// We do not need to check if any output is 0 bits.
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for ip >= 4 {
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s.bw.flush32()
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v3, v2, v1, v0 := src[ip-4], src[ip-3], src[ip-2], src[ip-1]
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c2.encode(tt[v0])
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c1.encode(tt[v1])
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c2.encode(tt[v2])
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c1.encode(tt[v3])
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ip -= 4
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}
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case !s.zeroBits:
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// We do not need to check if any output is 0 bits.
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for ip >= 4 {
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s.bw.flush32()
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v3, v2, v1, v0 := src[ip-4], src[ip-3], src[ip-2], src[ip-1]
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c2.encode(tt[v0])
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c1.encode(tt[v1])
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s.bw.flush32()
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c2.encode(tt[v2])
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c1.encode(tt[v3])
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ip -= 4
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}
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case s.actualTableLog <= 8:
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// We can encode 4 symbols without requiring a flush
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for ip >= 4 {
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s.bw.flush32()
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v3, v2, v1, v0 := src[ip-4], src[ip-3], src[ip-2], src[ip-1]
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c2.encodeZero(tt[v0])
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c1.encodeZero(tt[v1])
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c2.encodeZero(tt[v2])
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c1.encodeZero(tt[v3])
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ip -= 4
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}
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default:
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for ip >= 4 {
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s.bw.flush32()
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v3, v2, v1, v0 := src[ip-4], src[ip-3], src[ip-2], src[ip-1]
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c2.encodeZero(tt[v0])
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c1.encodeZero(tt[v1])
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s.bw.flush32()
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c2.encodeZero(tt[v2])
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c1.encodeZero(tt[v3])
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ip -= 4
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}
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}
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// Flush final state.
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// Used to initialize state when decoding.
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c2.flush(s.actualTableLog)
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c1.flush(s.actualTableLog)
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return s.bw.close()
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}
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// writeCount will write the normalized histogram count to header.
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// This is read back by readNCount.
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func (s *Scratch) writeCount() error {
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var (
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tableLog = s.actualTableLog
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tableSize = 1 << tableLog
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previous0 bool
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charnum uint16
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maxHeaderSize = ((int(s.symbolLen) * int(tableLog)) >> 3) + 3
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// Write Table Size
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bitStream = uint32(tableLog - minTablelog)
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bitCount = uint(4)
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remaining = int16(tableSize + 1) /* +1 for extra accuracy */
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threshold = int16(tableSize)
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nbBits = uint(tableLog + 1)
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)
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if cap(s.Out) < maxHeaderSize {
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s.Out = make([]byte, 0, s.br.remain()+maxHeaderSize)
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}
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outP := uint(0)
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out := s.Out[:maxHeaderSize]
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// stops at 1
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for remaining > 1 {
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if previous0 {
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start := charnum
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for s.norm[charnum] == 0 {
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charnum++
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}
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for charnum >= start+24 {
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start += 24
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bitStream += uint32(0xFFFF) << bitCount
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out[outP] = byte(bitStream)
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out[outP+1] = byte(bitStream >> 8)
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outP += 2
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bitStream >>= 16
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}
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for charnum >= start+3 {
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start += 3
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bitStream += 3 << bitCount
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bitCount += 2
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}
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bitStream += uint32(charnum-start) << bitCount
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bitCount += 2
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if bitCount > 16 {
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out[outP] = byte(bitStream)
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out[outP+1] = byte(bitStream >> 8)
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outP += 2
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bitStream >>= 16
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bitCount -= 16
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}
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}
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count := s.norm[charnum]
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charnum++
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max := (2*threshold - 1) - remaining
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if count < 0 {
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remaining += count
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} else {
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remaining -= count
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}
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count++ // +1 for extra accuracy
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if count >= threshold {
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count += max // [0..max[ [max..threshold[ (...) [threshold+max 2*threshold[
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}
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bitStream += uint32(count) << bitCount
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bitCount += nbBits
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if count < max {
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bitCount--
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}
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previous0 = count == 1
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if remaining < 1 {
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return errors.New("internal error: remaining<1")
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}
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for remaining < threshold {
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nbBits--
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threshold >>= 1
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}
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if bitCount > 16 {
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out[outP] = byte(bitStream)
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out[outP+1] = byte(bitStream >> 8)
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outP += 2
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bitStream >>= 16
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bitCount -= 16
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}
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}
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out[outP] = byte(bitStream)
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out[outP+1] = byte(bitStream >> 8)
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outP += (bitCount + 7) / 8
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if uint16(charnum) > s.symbolLen {
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return errors.New("internal error: charnum > s.symbolLen")
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}
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s.Out = out[:outP]
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return nil
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}
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// symbolTransform contains the state transform for a symbol.
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type symbolTransform struct {
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deltaFindState int32
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deltaNbBits uint32
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}
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// String prints values as a human readable string.
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func (s symbolTransform) String() string {
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return fmt.Sprintf("dnbits: %08x, fs:%d", s.deltaNbBits, s.deltaFindState)
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}
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// cTable contains tables used for compression.
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type cTable struct {
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tableSymbol []byte
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stateTable []uint16
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symbolTT []symbolTransform
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}
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// allocCtable will allocate tables needed for compression.
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// If existing tables a re big enough, they are simply re-used.
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func (s *Scratch) allocCtable() {
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tableSize := 1 << s.actualTableLog
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// get tableSymbol that is big enough.
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if cap(s.ct.tableSymbol) < int(tableSize) {
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s.ct.tableSymbol = make([]byte, tableSize)
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}
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s.ct.tableSymbol = s.ct.tableSymbol[:tableSize]
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ctSize := tableSize
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if cap(s.ct.stateTable) < ctSize {
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s.ct.stateTable = make([]uint16, ctSize)
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}
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s.ct.stateTable = s.ct.stateTable[:ctSize]
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if cap(s.ct.symbolTT) < 256 {
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s.ct.symbolTT = make([]symbolTransform, 256)
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}
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s.ct.symbolTT = s.ct.symbolTT[:256]
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}
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// buildCTable will populate the compression table so it is ready to be used.
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func (s *Scratch) buildCTable() error {
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tableSize := uint32(1 << s.actualTableLog)
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highThreshold := tableSize - 1
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var cumul [maxSymbolValue + 2]int16
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s.allocCtable()
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tableSymbol := s.ct.tableSymbol[:tableSize]
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// symbol start positions
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{
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cumul[0] = 0
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for ui, v := range s.norm[:s.symbolLen-1] {
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u := byte(ui) // one less than reference
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if v == -1 {
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// Low proba symbol
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cumul[u+1] = cumul[u] + 1
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tableSymbol[highThreshold] = u
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highThreshold--
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} else {
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cumul[u+1] = cumul[u] + v
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}
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}
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// Encode last symbol separately to avoid overflowing u
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u := int(s.symbolLen - 1)
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v := s.norm[s.symbolLen-1]
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if v == -1 {
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// Low proba symbol
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cumul[u+1] = cumul[u] + 1
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tableSymbol[highThreshold] = byte(u)
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highThreshold--
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} else {
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cumul[u+1] = cumul[u] + v
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}
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if uint32(cumul[s.symbolLen]) != tableSize {
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return fmt.Errorf("internal error: expected cumul[s.symbolLen] (%d) == tableSize (%d)", cumul[s.symbolLen], tableSize)
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}
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cumul[s.symbolLen] = int16(tableSize) + 1
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}
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// Spread symbols
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s.zeroBits = false
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{
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step := tableStep(tableSize)
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tableMask := tableSize - 1
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var position uint32
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// if any symbol > largeLimit, we may have 0 bits output.
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largeLimit := int16(1 << (s.actualTableLog - 1))
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for ui, v := range s.norm[:s.symbolLen] {
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symbol := byte(ui)
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if v > largeLimit {
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s.zeroBits = true
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}
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for nbOccurrences := int16(0); nbOccurrences < v; nbOccurrences++ {
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tableSymbol[position] = symbol
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position = (position + step) & tableMask
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for position > highThreshold {
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position = (position + step) & tableMask
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} /* Low proba area */
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}
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}
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// Check if we have gone through all positions
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if position != 0 {
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return errors.New("position!=0")
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}
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}
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// Build table
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table := s.ct.stateTable
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{
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tsi := int(tableSize)
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for u, v := range tableSymbol {
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// TableU16 : sorted by symbol order; gives next state value
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table[cumul[v]] = uint16(tsi + u)
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cumul[v]++
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}
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}
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// Build Symbol Transformation Table
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{
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total := int16(0)
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symbolTT := s.ct.symbolTT[:s.symbolLen]
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tableLog := s.actualTableLog
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tl := (uint32(tableLog) << 16) - (1 << tableLog)
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for i, v := range s.norm[:s.symbolLen] {
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switch v {
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case 0:
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case -1, 1:
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symbolTT[i].deltaNbBits = tl
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symbolTT[i].deltaFindState = int32(total - 1)
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total++
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default:
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maxBitsOut := uint32(tableLog) - highBits(uint32(v-1))
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minStatePlus := uint32(v) << maxBitsOut
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symbolTT[i].deltaNbBits = (maxBitsOut << 16) - minStatePlus
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symbolTT[i].deltaFindState = int32(total - v)
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total += v
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}
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}
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if total != int16(tableSize) {
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return fmt.Errorf("total mismatch %d (got) != %d (want)", total, tableSize)
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}
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}
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return nil
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}
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// countSimple will create a simple histogram in s.count.
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// Returns the biggest count.
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// Does not update s.clearCount.
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func (s *Scratch) countSimple(in []byte) (max int) {
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for _, v := range in {
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s.count[v]++
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}
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m := uint32(0)
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for i, v := range s.count[:] {
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if v > m {
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m = v
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}
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if v > 0 {
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s.symbolLen = uint16(i) + 1
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}
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}
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return int(m)
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}
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// minTableLog provides the minimum logSize to safely represent a distribution.
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func (s *Scratch) minTableLog() uint8 {
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minBitsSrc := highBits(uint32(s.br.remain()-1)) + 1
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minBitsSymbols := highBits(uint32(s.symbolLen-1)) + 2
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if minBitsSrc < minBitsSymbols {
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return uint8(minBitsSrc)
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}
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return uint8(minBitsSymbols)
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}
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// optimalTableLog calculates and sets the optimal tableLog in s.actualTableLog
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func (s *Scratch) optimalTableLog() {
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tableLog := s.TableLog
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minBits := s.minTableLog()
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maxBitsSrc := uint8(highBits(uint32(s.br.remain()-1))) - 2
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if maxBitsSrc < tableLog {
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// Accuracy can be reduced
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tableLog = maxBitsSrc
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}
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if minBits > tableLog {
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tableLog = minBits
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}
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// Need a minimum to safely represent all symbol values
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if tableLog < minTablelog {
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tableLog = minTablelog
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}
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if tableLog > maxTableLog {
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tableLog = maxTableLog
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}
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s.actualTableLog = tableLog
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}
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var rtbTable = [...]uint32{0, 473195, 504333, 520860, 550000, 700000, 750000, 830000}
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|
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// normalizeCount will normalize the count of the symbols so
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// the total is equal to the table size.
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func (s *Scratch) normalizeCount() error {
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var (
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tableLog = s.actualTableLog
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scale = 62 - uint64(tableLog)
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step = (1 << 62) / uint64(s.br.remain())
|
|
vStep = uint64(1) << (scale - 20)
|
|
stillToDistribute = int16(1 << tableLog)
|
|
largest int
|
|
largestP int16
|
|
lowThreshold = (uint32)(s.br.remain() >> tableLog)
|
|
)
|
|
|
|
for i, cnt := range s.count[:s.symbolLen] {
|
|
// already handled
|
|
// if (count[s] == s.length) return 0; /* rle special case */
|
|
|
|
if cnt == 0 {
|
|
s.norm[i] = 0
|
|
continue
|
|
}
|
|
if cnt <= lowThreshold {
|
|
s.norm[i] = -1
|
|
stillToDistribute--
|
|
} else {
|
|
proba := (int16)((uint64(cnt) * step) >> scale)
|
|
if proba < 8 {
|
|
restToBeat := vStep * uint64(rtbTable[proba])
|
|
v := uint64(cnt)*step - (uint64(proba) << scale)
|
|
if v > restToBeat {
|
|
proba++
|
|
}
|
|
}
|
|
if proba > largestP {
|
|
largestP = proba
|
|
largest = i
|
|
}
|
|
s.norm[i] = proba
|
|
stillToDistribute -= proba
|
|
}
|
|
}
|
|
|
|
if -stillToDistribute >= (s.norm[largest] >> 1) {
|
|
// corner case, need another normalization method
|
|
return s.normalizeCount2()
|
|
}
|
|
s.norm[largest] += stillToDistribute
|
|
return nil
|
|
}
|
|
|
|
// Secondary normalization method.
|
|
// To be used when primary method fails.
|
|
func (s *Scratch) normalizeCount2() error {
|
|
const notYetAssigned = -2
|
|
var (
|
|
distributed uint32
|
|
total = uint32(s.br.remain())
|
|
tableLog = s.actualTableLog
|
|
lowThreshold = uint32(total >> tableLog)
|
|
lowOne = uint32((total * 3) >> (tableLog + 1))
|
|
)
|
|
for i, cnt := range s.count[:s.symbolLen] {
|
|
if cnt == 0 {
|
|
s.norm[i] = 0
|
|
continue
|
|
}
|
|
if cnt <= lowThreshold {
|
|
s.norm[i] = -1
|
|
distributed++
|
|
total -= cnt
|
|
continue
|
|
}
|
|
if cnt <= lowOne {
|
|
s.norm[i] = 1
|
|
distributed++
|
|
total -= cnt
|
|
continue
|
|
}
|
|
s.norm[i] = notYetAssigned
|
|
}
|
|
toDistribute := (1 << tableLog) - distributed
|
|
|
|
if (total / toDistribute) > lowOne {
|
|
// risk of rounding to zero
|
|
lowOne = uint32((total * 3) / (toDistribute * 2))
|
|
for i, cnt := range s.count[:s.symbolLen] {
|
|
if (s.norm[i] == notYetAssigned) && (cnt <= lowOne) {
|
|
s.norm[i] = 1
|
|
distributed++
|
|
total -= cnt
|
|
continue
|
|
}
|
|
}
|
|
toDistribute = (1 << tableLog) - distributed
|
|
}
|
|
if distributed == uint32(s.symbolLen)+1 {
|
|
// all values are pretty poor;
|
|
// probably incompressible data (should have already been detected);
|
|
// find max, then give all remaining points to max
|
|
var maxV int
|
|
var maxC uint32
|
|
for i, cnt := range s.count[:s.symbolLen] {
|
|
if cnt > maxC {
|
|
maxV = i
|
|
maxC = cnt
|
|
}
|
|
}
|
|
s.norm[maxV] += int16(toDistribute)
|
|
return nil
|
|
}
|
|
|
|
if total == 0 {
|
|
// all of the symbols were low enough for the lowOne or lowThreshold
|
|
for i := uint32(0); toDistribute > 0; i = (i + 1) % (uint32(s.symbolLen)) {
|
|
if s.norm[i] > 0 {
|
|
toDistribute--
|
|
s.norm[i]++
|
|
}
|
|
}
|
|
return nil
|
|
}
|
|
|
|
var (
|
|
vStepLog = 62 - uint64(tableLog)
|
|
mid = uint64((1 << (vStepLog - 1)) - 1)
|
|
rStep = (((1 << vStepLog) * uint64(toDistribute)) + mid) / uint64(total) // scale on remaining
|
|
tmpTotal = mid
|
|
)
|
|
for i, cnt := range s.count[:s.symbolLen] {
|
|
if s.norm[i] == notYetAssigned {
|
|
var (
|
|
end = tmpTotal + uint64(cnt)*rStep
|
|
sStart = uint32(tmpTotal >> vStepLog)
|
|
sEnd = uint32(end >> vStepLog)
|
|
weight = sEnd - sStart
|
|
)
|
|
if weight < 1 {
|
|
return errors.New("weight < 1")
|
|
}
|
|
s.norm[i] = int16(weight)
|
|
tmpTotal = end
|
|
}
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// validateNorm validates the normalized histogram table.
|
|
func (s *Scratch) validateNorm() (err error) {
|
|
var total int
|
|
for _, v := range s.norm[:s.symbolLen] {
|
|
if v >= 0 {
|
|
total += int(v)
|
|
} else {
|
|
total -= int(v)
|
|
}
|
|
}
|
|
defer func() {
|
|
if err == nil {
|
|
return
|
|
}
|
|
fmt.Printf("selected TableLog: %d, Symbol length: %d\n", s.actualTableLog, s.symbolLen)
|
|
for i, v := range s.norm[:s.symbolLen] {
|
|
fmt.Printf("%3d: %5d -> %4d \n", i, s.count[i], v)
|
|
}
|
|
}()
|
|
if total != (1 << s.actualTableLog) {
|
|
return fmt.Errorf("warning: Total == %d != %d", total, 1<<s.actualTableLog)
|
|
}
|
|
for i, v := range s.count[s.symbolLen:] {
|
|
if v != 0 {
|
|
return fmt.Errorf("warning: Found symbol out of range, %d after cut", i)
|
|
}
|
|
}
|
|
return nil
|
|
}
|
|
|