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package server
import (
"io"
"math/bits"
"encoding/binary"
)
// the protocol requires us to send the level as a gzipped flat array. but our
// level representation is close to run length encoding that can be achieved
// with DEFLATE. it is thus significantly more CPU efficient to, instead of
// expanding out the RLE and compressing it with the generic compressor,
// translate it directly into DEFLATE
func deflateRuns(
wr io.Writer, runs []blockData, changes []blockData,
levelSize uint32) (length uint32, err error) {
bw := bitsWriter {wr: wr}
bw.Write(0b011, 3) // BFINAL, fixed huffman
writeCode(&bw, 0xff & (levelSize >> 24))
writeCode(&bw, 0xff & (levelSize >> 16))
writeCode(&bw, 0xff & (levelSize >> 8))
err = writeCode(&bw, 0xff & levelSize)
if err != nil {
return
}
for i, data := range runs {
var nextPos uint32
if i < len(runs) - 1 {
nextPos = runs[i + 1].Pos
} else {
nextPos = levelSize
}
curPos := data.Pos
for len(changes) > 0 {
ch := changes[0]
if ch.Pos >= nextPos {
break
}
changes = changes[1:]
writeRun(&bw, byte(data.Block), ch.Pos - curPos)
err = writeRun(&bw, byte(ch.Block), 1)
if err != nil {
return
}
curPos = ch.Pos + 1
}
if curPos < nextPos {
err = writeRun(&bw, byte(data.Block), nextPos - curPos)
if err != nil {
return
}
}
}
writeCode(&bw, 256)
return levelSize + 4, bw.Close()
}
var lengthExtraBits = [...]uint8{
/* 257 */ 0, 0, 0,
/* 260 */ 0, 0, 0, 0, 0, 1, 1, 1, 1, 2,
/* 270 */ 2, 2, 2, 3, 3, 3, 3, 4, 4, 4,
/* 280 */ 4, 5, 5, 5, 5, 0,
}
var lengthBase = [...]uint32{
0, 1, 2, 3, 4, 5, 6, 7, 8, 10,
12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
64, 80, 96, 112, 128, 160, 192, 224, 255,
}
var lengthCodes = [...]uint32{
0, 1, 2, 3, 4, 5, 6, 7, 8, 8,
9, 9, 10, 10, 11, 11, 12, 12, 12, 12,
13, 13, 13, 13, 14, 14, 14, 14, 15, 15,
15, 15, 16, 16, 16, 16, 16, 16, 16, 16,
17, 17, 17, 17, 17, 17, 17, 17, 18, 18,
18, 18, 18, 18, 18, 18, 19, 19, 19, 19,
19, 19, 19, 19, 20, 20, 20, 20, 20, 20,
20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
21, 21, 21, 21, 21, 21, 21, 21, 21, 21,
21, 21, 21, 21, 21, 21, 22, 22, 22, 22,
22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
22, 22, 23, 23, 23, 23, 23, 23, 23, 23,
23, 23, 23, 23, 23, 23, 23, 23, 24, 24,
24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
25, 25, 26, 26, 26, 26, 26, 26, 26, 26,
26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
26, 26, 26, 26, 27, 27, 27, 27, 27, 27,
27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
27, 27, 27, 27, 27, 28,
}
func writeRun(bw *bitsWriter, value byte, totalLen uint32) error {
var err error
for totalLen > 0 {
len := min(totalLen, 258)
if len < 4 {
for i := 0; i < int(len); i++ {
err = writeCode(bw, uint32(value))
}
} else {
writeCode(bw, uint32(value))
writeLength(bw, len - 1)
err = bw.Write(0b00000, 5) // distance: 1
}
totalLen -= len
}
return err
}
func writeLength(bw *bitsWriter, length uint32) error {
length -= 3
code := lengthCodes[length]
writeCode(bw, 257 + code)
return bw.Write(length - lengthBase[code], lengthExtraBits[code])
}
func writeCode(bw *bitsWriter, v uint32) error {
var code uint32
var size uint8
switch {
case v < 144:
// size 8, 000110000 .. 10111111
code = v + 48
size = 8
case v < 256:
// size 9, 110010000 .. 111111111
code = v + 400 - 144
size = 9
case v < 280:
// size 7, 0000000 .. 0010111
code = v - 256
size = 7
case v < 288:
// size 8, 11000000 .. 11000111
code = v + 192 - 280
size = 8
default:
panic("code value out of range")
}
code = bits.Reverse32(code << (32 - size))
return bw.Write(code, size)
}
type bitsWriter struct {
wr io.Writer
buf uint64
nbuf byte
}
func (bw *bitsWriter) Write(v uint32, n uint8) error {
if 64 - bw.nbuf < n {
err := bw.writeBuf()
if err != nil {
return err
}
}
bw.buf |= uint64(v & ((1<<n)-1)) << bw.nbuf
bw.nbuf += n
return nil
}
func (bw *bitsWriter) writeBuf() error {
var bytes [8]byte
binary.LittleEndian.PutUint64(bytes[:], bw.buf)
nbytes := bw.nbuf / 8
_, err := bw.wr.Write(bytes[:nbytes])
bw.buf >>= nbytes * 8
bw.nbuf -= nbytes * 8
return err
}
func (bw *bitsWriter) Close() error {
if bw.nbuf > 0 {
bw.Write(0, 8 - (bw.nbuf % 8))
}
return bw.writeBuf()
}
func writePointlessGzipHeader(wr io.Writer) error {
var header = [10]byte {
0x1f, 0x8b,
0x08,
0x00,
0x00, 0x00, 0x00, 0x00,
0x00,
0x09,
}
_, err := wr.Write(header[:])
return err
}
func writePointlessGzipTrailer(wr io.Writer, length uint32) error {
var trailer [8]byte
binary.LittleEndian.PutUint32(trailer[0:], 0xffffffff)
binary.LittleEndian.PutUint32(trailer[4:], length)
_, err := wr.Write(trailer[:])
return err
}
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