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651 lines
16 KiB
651 lines
16 KiB
package huff0
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import (
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"fmt"
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"runtime"
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"sync"
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)
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// Compress1X will compress the input.
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// The output can be decoded using Decompress1X.
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// Supply a Scratch object. The scratch object contains state about re-use,
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// So when sharing across independent encodes, be sure to set the re-use policy.
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func Compress1X(in []byte, s *Scratch) (out []byte, reUsed bool, err error) {
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s, err = s.prepare(in)
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if err != nil {
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return nil, false, err
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}
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return compress(in, s, s.compress1X)
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}
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// Compress4X will compress the input. The input is split into 4 independent blocks
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// and compressed similar to Compress1X.
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// The output can be decoded using Decompress4X.
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// Supply a Scratch object. The scratch object contains state about re-use,
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// So when sharing across independent encodes, be sure to set the re-use policy.
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func Compress4X(in []byte, s *Scratch) (out []byte, reUsed bool, err error) {
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s, err = s.prepare(in)
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if err != nil {
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return nil, false, err
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}
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if false {
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// TODO: compress4Xp only slightly faster.
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const parallelThreshold = 8 << 10
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if len(in) < parallelThreshold || runtime.GOMAXPROCS(0) == 1 {
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return compress(in, s, s.compress4X)
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}
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return compress(in, s, s.compress4Xp)
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}
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return compress(in, s, s.compress4X)
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}
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func compress(in []byte, s *Scratch, compressor func(src []byte) ([]byte, error)) (out []byte, reUsed bool, err error) {
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// Nuke previous table if we cannot reuse anyway.
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if s.Reuse == ReusePolicyNone {
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s.prevTable = s.prevTable[:0]
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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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var canReuse = false
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if maxCount == 0 {
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maxCount, canReuse = s.countSimple(in)
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} else {
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canReuse = s.canUseTable(s.prevTable)
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}
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// We want the output size to be less than this:
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wantSize := len(in)
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if s.WantLogLess > 0 {
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wantSize -= wantSize >> s.WantLogLess
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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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if maxCount > len(in) {
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return nil, false, fmt.Errorf("maxCount (%d) > length (%d)", maxCount, len(in))
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}
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if len(in) == 1 {
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return nil, false, ErrIncompressible
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}
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// One symbol, use RLE
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return nil, false, 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, false, ErrIncompressible
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}
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if s.Reuse == ReusePolicyPrefer && canReuse {
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keepTable := s.cTable
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keepTL := s.actualTableLog
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s.cTable = s.prevTable
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s.actualTableLog = s.prevTableLog
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s.Out, err = compressor(in)
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s.cTable = keepTable
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s.actualTableLog = keepTL
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if err == nil && len(s.Out) < wantSize {
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s.OutData = s.Out
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return s.Out, true, nil
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}
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// Do not attempt to re-use later.
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s.prevTable = s.prevTable[:0]
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}
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// Calculate new table.
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err = s.buildCTable()
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if err != nil {
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return nil, false, err
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}
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if false && !s.canUseTable(s.cTable) {
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panic("invalid table generated")
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}
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if s.Reuse == ReusePolicyAllow && canReuse {
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hSize := len(s.Out)
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oldSize := s.prevTable.estimateSize(s.count[:s.symbolLen])
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newSize := s.cTable.estimateSize(s.count[:s.symbolLen])
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if oldSize <= hSize+newSize || hSize+12 >= wantSize {
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// Retain cTable even if we re-use.
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keepTable := s.cTable
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keepTL := s.actualTableLog
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s.cTable = s.prevTable
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s.actualTableLog = s.prevTableLog
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s.Out, err = compressor(in)
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// Restore ctable.
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s.cTable = keepTable
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s.actualTableLog = keepTL
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if err != nil {
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return nil, false, err
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}
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if len(s.Out) >= wantSize {
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return nil, false, ErrIncompressible
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}
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s.OutData = s.Out
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return s.Out, true, nil
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}
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}
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// Use new table
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err = s.cTable.write(s)
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if err != nil {
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s.OutTable = nil
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return nil, false, err
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}
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s.OutTable = s.Out
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// Compress using new table
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s.Out, err = compressor(in)
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if err != nil {
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s.OutTable = nil
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return nil, false, err
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}
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if len(s.Out) >= wantSize {
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s.OutTable = nil
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return nil, false, ErrIncompressible
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}
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// Move current table into previous.
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s.prevTable, s.prevTableLog, s.cTable = s.cTable, s.actualTableLog, s.prevTable[:0]
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s.OutData = s.Out[len(s.OutTable):]
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return s.Out, false, nil
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}
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func (s *Scratch) compress1X(src []byte) ([]byte, error) {
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return s.compress1xDo(s.Out, src)
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}
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func (s *Scratch) compress1xDo(dst, src []byte) ([]byte, error) {
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var bw = bitWriter{out: dst}
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// N is length divisible by 4.
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n := len(src)
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n -= n & 3
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cTable := s.cTable[:256]
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// Encode last bytes.
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for i := len(src) & 3; i > 0; i-- {
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bw.encSymbol(cTable, src[n+i-1])
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}
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n -= 4
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if s.actualTableLog <= 8 {
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for ; n >= 0; n -= 4 {
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tmp := src[n : n+4]
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// tmp should be len 4
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bw.flush32()
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bw.encTwoSymbols(cTable, tmp[3], tmp[2])
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bw.encTwoSymbols(cTable, tmp[1], tmp[0])
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}
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} else {
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for ; n >= 0; n -= 4 {
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tmp := src[n : n+4]
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// tmp should be len 4
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bw.flush32()
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bw.encTwoSymbols(cTable, tmp[3], tmp[2])
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bw.flush32()
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bw.encTwoSymbols(cTable, tmp[1], tmp[0])
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}
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}
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err := bw.close()
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return bw.out, err
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}
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var sixZeros [6]byte
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func (s *Scratch) compress4X(src []byte) ([]byte, error) {
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if len(src) < 12 {
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return nil, ErrIncompressible
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}
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segmentSize := (len(src) + 3) / 4
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// Add placeholder for output length
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offsetIdx := len(s.Out)
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s.Out = append(s.Out, sixZeros[:]...)
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for i := 0; i < 4; i++ {
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toDo := src
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if len(toDo) > segmentSize {
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toDo = toDo[:segmentSize]
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}
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src = src[len(toDo):]
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var err error
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idx := len(s.Out)
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s.Out, err = s.compress1xDo(s.Out, toDo)
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if err != nil {
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return nil, err
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}
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// Write compressed length as little endian before block.
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if i < 3 {
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// Last length is not written.
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length := len(s.Out) - idx
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s.Out[i*2+offsetIdx] = byte(length)
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s.Out[i*2+offsetIdx+1] = byte(length >> 8)
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}
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}
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return s.Out, nil
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}
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// compress4Xp will compress 4 streams using separate goroutines.
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func (s *Scratch) compress4Xp(src []byte) ([]byte, error) {
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if len(src) < 12 {
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return nil, ErrIncompressible
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}
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// Add placeholder for output length
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s.Out = s.Out[:6]
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segmentSize := (len(src) + 3) / 4
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var wg sync.WaitGroup
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var errs [4]error
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wg.Add(4)
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for i := 0; i < 4; i++ {
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toDo := src
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if len(toDo) > segmentSize {
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toDo = toDo[:segmentSize]
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}
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src = src[len(toDo):]
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// Separate goroutine for each block.
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go func(i int) {
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s.tmpOut[i], errs[i] = s.compress1xDo(s.tmpOut[i][:0], toDo)
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wg.Done()
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}(i)
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}
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wg.Wait()
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for i := 0; i < 4; i++ {
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if errs[i] != nil {
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return nil, errs[i]
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}
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o := s.tmpOut[i]
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// Write compressed length as little endian before block.
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if i < 3 {
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// Last length is not written.
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s.Out[i*2] = byte(len(o))
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s.Out[i*2+1] = byte(len(o) >> 8)
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}
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// Write output.
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s.Out = append(s.Out, o...)
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}
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return s.Out, 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, reuse bool) {
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reuse = true
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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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if len(s.prevTable) > 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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if i >= len(s.prevTable) {
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reuse = false
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} else {
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if s.prevTable[i].nBits == 0 {
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reuse = false
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}
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}
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}
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}
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return int(m), reuse
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}
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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), false
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}
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func (s *Scratch) canUseTable(c cTable) bool {
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if len(c) < int(s.symbolLen) {
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return false
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}
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for i, v := range s.count[:s.symbolLen] {
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if v != 0 && c[i].nBits == 0 {
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return false
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}
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}
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return true
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}
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func (s *Scratch) validateTable(c cTable) bool {
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if len(c) < int(s.symbolLen) {
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return false
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}
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for i, v := range s.count[:s.symbolLen] {
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if v != 0 {
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if c[i].nBits == 0 {
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return false
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}
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if c[i].nBits > s.actualTableLog {
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return false
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}
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}
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}
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return true
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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 := highBit32(uint32(s.br.remain())) + 1
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minBitsSymbols := highBit32(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(highBit32(uint32(s.br.remain()-1))) - 1
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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 > tableLogMax {
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tableLog = tableLogMax
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}
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s.actualTableLog = tableLog
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}
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type cTableEntry struct {
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val uint16
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nBits uint8
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// We have 8 bits extra
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}
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const huffNodesMask = huffNodesLen - 1
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func (s *Scratch) buildCTable() error {
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s.optimalTableLog()
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s.huffSort()
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if cap(s.cTable) < maxSymbolValue+1 {
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s.cTable = make([]cTableEntry, s.symbolLen, maxSymbolValue+1)
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} else {
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s.cTable = s.cTable[:s.symbolLen]
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for i := range s.cTable {
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s.cTable[i] = cTableEntry{}
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}
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}
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var startNode = int16(s.symbolLen)
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nonNullRank := s.symbolLen - 1
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nodeNb := int16(startNode)
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huffNode := s.nodes[1 : huffNodesLen+1]
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// This overlays the slice above, but allows "-1" index lookups.
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// Different from reference implementation.
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huffNode0 := s.nodes[0 : huffNodesLen+1]
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for huffNode[nonNullRank].count == 0 {
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nonNullRank--
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}
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lowS := int16(nonNullRank)
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nodeRoot := nodeNb + lowS - 1
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lowN := nodeNb
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huffNode[nodeNb].count = huffNode[lowS].count + huffNode[lowS-1].count
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huffNode[lowS].parent, huffNode[lowS-1].parent = uint16(nodeNb), uint16(nodeNb)
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nodeNb++
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lowS -= 2
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for n := nodeNb; n <= nodeRoot; n++ {
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huffNode[n].count = 1 << 30
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}
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// fake entry, strong barrier
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huffNode0[0].count = 1 << 31
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// create parents
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for nodeNb <= nodeRoot {
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var n1, n2 int16
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if huffNode0[lowS+1].count < huffNode0[lowN+1].count {
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n1 = lowS
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lowS--
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} else {
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n1 = lowN
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lowN++
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}
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if huffNode0[lowS+1].count < huffNode0[lowN+1].count {
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n2 = lowS
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lowS--
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} else {
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n2 = lowN
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lowN++
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}
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huffNode[nodeNb].count = huffNode0[n1+1].count + huffNode0[n2+1].count
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huffNode0[n1+1].parent, huffNode0[n2+1].parent = uint16(nodeNb), uint16(nodeNb)
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nodeNb++
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}
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// distribute weights (unlimited tree height)
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huffNode[nodeRoot].nbBits = 0
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for n := nodeRoot - 1; n >= startNode; n-- {
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huffNode[n].nbBits = huffNode[huffNode[n].parent].nbBits + 1
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}
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for n := uint16(0); n <= nonNullRank; n++ {
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huffNode[n].nbBits = huffNode[huffNode[n].parent].nbBits + 1
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}
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s.actualTableLog = s.setMaxHeight(int(nonNullRank))
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maxNbBits := s.actualTableLog
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// fill result into tree (val, nbBits)
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if maxNbBits > tableLogMax {
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return fmt.Errorf("internal error: maxNbBits (%d) > tableLogMax (%d)", maxNbBits, tableLogMax)
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}
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var nbPerRank [tableLogMax + 1]uint16
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var valPerRank [16]uint16
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for _, v := range huffNode[:nonNullRank+1] {
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nbPerRank[v.nbBits]++
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}
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// determine stating value per rank
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{
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min := uint16(0)
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for n := maxNbBits; n > 0; n-- {
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// get starting value within each rank
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valPerRank[n] = min
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min += nbPerRank[n]
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min >>= 1
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}
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}
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// push nbBits per symbol, symbol order
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for _, v := range huffNode[:nonNullRank+1] {
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s.cTable[v.symbol].nBits = v.nbBits
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}
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// assign value within rank, symbol order
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t := s.cTable[:s.symbolLen]
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for n, val := range t {
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nbits := val.nBits & 15
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v := valPerRank[nbits]
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t[n].val = v
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valPerRank[nbits] = v + 1
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}
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return nil
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}
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// huffSort will sort symbols, decreasing order.
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func (s *Scratch) huffSort() {
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type rankPos struct {
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base uint32
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current uint32
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}
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// Clear nodes
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nodes := s.nodes[:huffNodesLen+1]
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s.nodes = nodes
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nodes = nodes[1 : huffNodesLen+1]
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// Sort into buckets based on length of symbol count.
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var rank [32]rankPos
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for _, v := range s.count[:s.symbolLen] {
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r := highBit32(v+1) & 31
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rank[r].base++
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}
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// maxBitLength is log2(BlockSizeMax) + 1
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const maxBitLength = 18 + 1
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for n := maxBitLength; n > 0; n-- {
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rank[n-1].base += rank[n].base
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}
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for n := range rank[:maxBitLength] {
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rank[n].current = rank[n].base
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}
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for n, c := range s.count[:s.symbolLen] {
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r := (highBit32(c+1) + 1) & 31
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pos := rank[r].current
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rank[r].current++
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prev := nodes[(pos-1)&huffNodesMask]
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for pos > rank[r].base && c > prev.count {
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nodes[pos&huffNodesMask] = prev
|
|
pos--
|
|
prev = nodes[(pos-1)&huffNodesMask]
|
|
}
|
|
nodes[pos&huffNodesMask] = nodeElt{count: c, symbol: byte(n)}
|
|
}
|
|
return
|
|
}
|
|
|
|
func (s *Scratch) setMaxHeight(lastNonNull int) uint8 {
|
|
maxNbBits := s.actualTableLog
|
|
huffNode := s.nodes[1 : huffNodesLen+1]
|
|
//huffNode = huffNode[: huffNodesLen]
|
|
|
|
largestBits := huffNode[lastNonNull].nbBits
|
|
|
|
// early exit : no elt > maxNbBits
|
|
if largestBits <= maxNbBits {
|
|
return largestBits
|
|
}
|
|
totalCost := int(0)
|
|
baseCost := int(1) << (largestBits - maxNbBits)
|
|
n := uint32(lastNonNull)
|
|
|
|
for huffNode[n].nbBits > maxNbBits {
|
|
totalCost += baseCost - (1 << (largestBits - huffNode[n].nbBits))
|
|
huffNode[n].nbBits = maxNbBits
|
|
n--
|
|
}
|
|
// n stops at huffNode[n].nbBits <= maxNbBits
|
|
|
|
for huffNode[n].nbBits == maxNbBits {
|
|
n--
|
|
}
|
|
// n end at index of smallest symbol using < maxNbBits
|
|
|
|
// renorm totalCost
|
|
totalCost >>= largestBits - maxNbBits /* note : totalCost is necessarily a multiple of baseCost */
|
|
|
|
// repay normalized cost
|
|
{
|
|
const noSymbol = 0xF0F0F0F0
|
|
var rankLast [tableLogMax + 2]uint32
|
|
|
|
for i := range rankLast[:] {
|
|
rankLast[i] = noSymbol
|
|
}
|
|
|
|
// Get pos of last (smallest) symbol per rank
|
|
{
|
|
currentNbBits := uint8(maxNbBits)
|
|
for pos := int(n); pos >= 0; pos-- {
|
|
if huffNode[pos].nbBits >= currentNbBits {
|
|
continue
|
|
}
|
|
currentNbBits = huffNode[pos].nbBits // < maxNbBits
|
|
rankLast[maxNbBits-currentNbBits] = uint32(pos)
|
|
}
|
|
}
|
|
|
|
for totalCost > 0 {
|
|
nBitsToDecrease := uint8(highBit32(uint32(totalCost))) + 1
|
|
|
|
for ; nBitsToDecrease > 1; nBitsToDecrease-- {
|
|
highPos := rankLast[nBitsToDecrease]
|
|
lowPos := rankLast[nBitsToDecrease-1]
|
|
if highPos == noSymbol {
|
|
continue
|
|
}
|
|
if lowPos == noSymbol {
|
|
break
|
|
}
|
|
highTotal := huffNode[highPos].count
|
|
lowTotal := 2 * huffNode[lowPos].count
|
|
if highTotal <= lowTotal {
|
|
break
|
|
}
|
|
}
|
|
// only triggered when no more rank 1 symbol left => find closest one (note : there is necessarily at least one !)
|
|
// HUF_MAX_TABLELOG test just to please gcc 5+; but it should not be necessary
|
|
// FIXME: try to remove
|
|
for (nBitsToDecrease <= tableLogMax) && (rankLast[nBitsToDecrease] == noSymbol) {
|
|
nBitsToDecrease++
|
|
}
|
|
totalCost -= 1 << (nBitsToDecrease - 1)
|
|
if rankLast[nBitsToDecrease-1] == noSymbol {
|
|
// this rank is no longer empty
|
|
rankLast[nBitsToDecrease-1] = rankLast[nBitsToDecrease]
|
|
}
|
|
huffNode[rankLast[nBitsToDecrease]].nbBits++
|
|
if rankLast[nBitsToDecrease] == 0 {
|
|
/* special case, reached largest symbol */
|
|
rankLast[nBitsToDecrease] = noSymbol
|
|
} else {
|
|
rankLast[nBitsToDecrease]--
|
|
if huffNode[rankLast[nBitsToDecrease]].nbBits != maxNbBits-nBitsToDecrease {
|
|
rankLast[nBitsToDecrease] = noSymbol /* this rank is now empty */
|
|
}
|
|
}
|
|
}
|
|
|
|
for totalCost < 0 { /* Sometimes, cost correction overshoot */
|
|
if rankLast[1] == noSymbol { /* special case : no rank 1 symbol (using maxNbBits-1); let's create one from largest rank 0 (using maxNbBits) */
|
|
for huffNode[n].nbBits == maxNbBits {
|
|
n--
|
|
}
|
|
huffNode[n+1].nbBits--
|
|
rankLast[1] = n + 1
|
|
totalCost++
|
|
continue
|
|
}
|
|
huffNode[rankLast[1]+1].nbBits--
|
|
rankLast[1]++
|
|
totalCost++
|
|
}
|
|
}
|
|
return maxNbBits
|
|
}
|
|
|
|
type nodeElt struct {
|
|
count uint32
|
|
parent uint16
|
|
symbol byte
|
|
nbBits uint8
|
|
}
|
|
|