/
writer.go
304 lines (268 loc) · 6.75 KB
/
writer.go
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package bzip2
import (
"io"
"github.com/marco-spagnuolo/unisacompression/internal"
"github.com/marco-spagnuolo/unisacompression/internal/errors"
"github.com/marco-spagnuolo/unisacompression/internal/prefix"
)
type Writer struct {
InputOffset int64 // Total number of bytes issued to Write
OutputOffset int64 // Total number of bytes written to underlying io.Writer
wr prefixWriter
err error
level int // The current compression level
wrHdr bool // Have we written the stream header?
blkCRC uint32 // CRC-32 IEEE of each block
endCRC uint32 // Checksum of all blocks using bzip2's custom method
crc crc
rle runLengthEncoding
bwt burrowsWheelerTransform
mtf moveToFront
// These fields are allocated with Writer and re-used later.
buf []byte
treeSels []uint8
treeSelsMTF []uint8
codes2D [maxNumTrees][maxNumSyms]prefix.PrefixCode
codes1D [maxNumTrees]prefix.PrefixCodes
trees1D [maxNumTrees]prefix.Encoder
}
type WriterConfig struct {
Level int
_ struct{} // Blank field to prevent unkeyed struct literals
}
func NewWriter(w io.Writer, conf *WriterConfig) (*Writer, error) {
var lvl int
if conf != nil {
lvl = conf.Level
}
if lvl == 0 {
lvl = DefaultCompression
}
if lvl < BestSpeed || lvl > BestCompression {
return nil, errorf(errors.Invalid, "compression level: %d", lvl)
}
zw := new(Writer)
zw.level = lvl
zw.Reset(w)
return zw, nil
}
func (zw *Writer) Reset(w io.Writer) error {
*zw = Writer{
wr: zw.wr,
level: zw.level,
rle: zw.rle,
bwt: zw.bwt,
mtf: zw.mtf,
buf: zw.buf,
treeSels: zw.treeSels,
treeSelsMTF: zw.treeSelsMTF,
trees1D: zw.trees1D,
}
zw.wr.Init(w)
if len(zw.buf) != zw.level*blockSize {
zw.buf = make([]byte, zw.level*blockSize)
}
zw.rle.Init(zw.buf)
return nil
}
func (zw *Writer) Write(buf []byte) (int, error) {
if zw.err != nil {
return 0, zw.err
}
cnt := len(buf)
for {
wrCnt, err := zw.rle.Write(buf)
if err != rleDone && zw.err == nil {
zw.err = err
}
zw.crc.update(buf[:wrCnt])
buf = buf[wrCnt:]
if len(buf) == 0 {
zw.InputOffset += int64(cnt)
return cnt, nil
}
if zw.err = zw.flush(); zw.err != nil {
return 0, zw.err
}
}
}
func (zw *Writer) flush() error {
vals := zw.rle.Bytes()
if len(vals) == 0 {
return nil
}
zw.wr.Offset = zw.OutputOffset
func() {
defer errors.Recover(&zw.err)
if !zw.wrHdr {
// Write stream header.
zw.wr.WriteBitsBE64(hdrMagic, 16)
zw.wr.WriteBitsBE64('h', 8)
zw.wr.WriteBitsBE64(uint64('0'+zw.level), 8)
zw.wrHdr = true
}
zw.encodeBlock(vals)
}()
var err error
if zw.OutputOffset, err = zw.wr.Flush(); zw.err == nil {
zw.err = err
}
if zw.err != nil {
zw.err = errWrap(zw.err, errors.Internal)
return zw.err
}
zw.endCRC = (zw.endCRC<<1 | zw.endCRC>>31) ^ zw.blkCRC
zw.blkCRC = 0
zw.rle.Init(zw.buf)
return nil
}
func (zw *Writer) Close() error {
if zw.err == errClosed {
return nil
}
// Flush RLE buffer if there is left-over data.
if zw.err = zw.flush(); zw.err != nil {
return zw.err
}
// Write stream footer.
zw.wr.Offset = zw.OutputOffset
func() {
defer errors.Recover(&zw.err)
if !zw.wrHdr {
// Write stream header.
zw.wr.WriteBitsBE64(hdrMagic, 16)
zw.wr.WriteBitsBE64('h', 8)
zw.wr.WriteBitsBE64(uint64('0'+zw.level), 8)
zw.wrHdr = true
}
zw.wr.WriteBitsBE64(endMagic, 48)
zw.wr.WriteBitsBE64(uint64(zw.endCRC), 32)
zw.wr.WritePads(0)
}()
var err error
if zw.OutputOffset, err = zw.wr.Flush(); zw.err == nil {
zw.err = err
}
if zw.err != nil {
zw.err = errWrap(zw.err, errors.Internal)
return zw.err
}
zw.err = errClosed
return nil
}
func (zw *Writer) encodeBlock(buf []byte) {
zw.blkCRC = zw.crc.val
zw.wr.WriteBitsBE64(blkMagic, 48)
zw.wr.WriteBitsBE64(uint64(zw.blkCRC), 32)
zw.wr.WriteBitsBE64(0, 1)
zw.crc.val = 0
// Step 1: Burrows-Wheeler transformation.
ptr := zw.bwt.Encode(buf)
zw.wr.WriteBitsBE64(uint64(ptr), 24)
// Step 2: Move-to-front transform and run-length encoding.
var dictMap [256]bool
for _, c := range buf {
dictMap[c] = true
}
var dictArr [256]uint8
var bmapLo [16]uint16
dict := dictArr[:0]
bmapHi := uint16(0)
for i, b := range dictMap {
if b {
c := uint8(i)
dict = append(dict, c)
bmapHi |= 1 << (c >> 4)
bmapLo[c>>4] |= 1 << (c & 0xf)
}
}
zw.wr.WriteBits(uint(bmapHi), 16)
for _, m := range bmapLo {
if m > 0 {
zw.wr.WriteBits(uint(m), 16)
}
}
zw.mtf.Init(dict, len(buf))
syms := zw.mtf.Encode(buf)
// Step 3: Prefix encoding.
zw.encodePrefix(syms, len(dict))
}
func (zw *Writer) encodePrefix(syms []uint16, numSyms int) {
numSyms += 2 // Remove 0 symbol, add RUNA, RUNB, and EOB symbols
if numSyms < 3 {
panicf(errors.Internal, "unable to encode EOB marker")
}
syms = append(syms, uint16(numSyms-1)) // EOB marker
// Compute number of prefix trees needed.
numTrees := maxNumTrees
for i, lim := range []int{200, 600, 1200, 2400} {
if len(syms) < lim {
numTrees = minNumTrees + i
break
}
}
// Compute number of block selectors.
numSels := (len(syms) + numBlockSyms - 1) / numBlockSyms
if cap(zw.treeSels) < numSels {
zw.treeSels = make([]uint8, numSels)
}
treeSels := zw.treeSels[:numSels]
for i := range treeSels {
treeSels[i] = uint8(i % numTrees)
}
// Initialize prefix codes.
for i := range zw.codes2D[:numTrees] {
pc := zw.codes2D[i][:numSyms]
for j := range pc {
pc[j] = prefix.PrefixCode{Sym: uint32(j)}
}
zw.codes1D[i] = pc
}
// First cut at assigning prefix trees to each group.
var codes prefix.PrefixCodes
var blkLen, selIdx int
for _, sym := range syms {
if blkLen == 0 {
blkLen = numBlockSyms
codes = zw.codes2D[treeSels[selIdx]][:numSyms]
selIdx++
}
blkLen--
codes[sym].Cnt++
}
// TODO(dsnet): Use K-means to cluster groups to each prefix tree.
// Generate lengths and prefixes based on symbol frequencies.
for i := range zw.trees1D[:numTrees] {
pc := prefix.PrefixCodes(zw.codes2D[i][:numSyms])
pc.SortByCount()
if err := prefix.GenerateLengths(pc, maxPrefixBits); err != nil {
errors.Panic(err)
}
pc.SortBySymbol()
}
// Write out information about the trees and tree selectors.
var mtf internal.MoveToFront
zw.wr.WriteBitsBE64(uint64(numTrees), 3)
zw.wr.WriteBitsBE64(uint64(numSels), 15)
zw.treeSelsMTF = append(zw.treeSelsMTF[:0], treeSels...)
mtf.Encode(zw.treeSelsMTF)
for _, sym := range zw.treeSelsMTF {
zw.wr.WriteSymbol(uint(sym), &encSel)
}
zw.wr.WritePrefixCodes(zw.codes1D[:numTrees], zw.trees1D[:numTrees])
// Write out prefix encoded symbols of compressed data.
var tree *prefix.Encoder
blkLen, selIdx = 0, 0
for _, sym := range syms {
if blkLen == 0 {
blkLen = numBlockSyms
tree = &zw.trees1D[treeSels[selIdx]]
selIdx++
}
blkLen--
ok := zw.wr.TryWriteSymbol(uint(sym), tree)
if !ok {
zw.wr.WriteSymbol(uint(sym), tree)
}
}
}