diff --git a/src/compress/flate/copy.go b/src/compress/flate/copy.go deleted file mode 100644 index a3200a8f49..0000000000 --- a/src/compress/flate/copy.go +++ /dev/null @@ -1,32 +0,0 @@ -// Copyright 2012 The Go Authors. All rights reserved. -// Use of this source code is governed by a BSD-style -// license that can be found in the LICENSE file. - -package flate - -// forwardCopy is like the built-in copy function except that it always goes -// forward from the start, even if the dst and src overlap. -// It is equivalent to: -// for i := 0; i < n; i++ { -// mem[dst+i] = mem[src+i] -// } -func forwardCopy(mem []byte, dst, src, n int) { - if dst <= src { - copy(mem[dst:dst+n], mem[src:src+n]) - return - } - for { - if dst >= src+n { - copy(mem[dst:dst+n], mem[src:src+n]) - return - } - // There is some forward overlap. The destination - // will be filled with a repeated pattern of mem[src:src+k]. - // We copy one instance of the pattern here, then repeat. - // Each time around this loop k will double. - k := dst - src - copy(mem[dst:dst+k], mem[src:src+k]) - n -= k - dst += k - } -} diff --git a/src/compress/flate/copy_test.go b/src/compress/flate/copy_test.go deleted file mode 100644 index 2011b1547c..0000000000 --- a/src/compress/flate/copy_test.go +++ /dev/null @@ -1,54 +0,0 @@ -// Copyright 2012 The Go Authors. All rights reserved. -// Use of this source code is governed by a BSD-style -// license that can be found in the LICENSE file. - -package flate - -import ( - "testing" -) - -func TestForwardCopy(t *testing.T) { - testCases := []struct { - dst0, dst1 int - src0, src1 int - want string - }{ - {0, 9, 0, 9, "012345678"}, - {0, 5, 4, 9, "45678"}, - {4, 9, 0, 5, "01230"}, - {1, 6, 3, 8, "34567"}, - {3, 8, 1, 6, "12121"}, - {0, 9, 3, 6, "345"}, - {3, 6, 0, 9, "012"}, - {1, 6, 0, 9, "00000"}, - {0, 4, 7, 8, "7"}, - {0, 1, 6, 8, "6"}, - {4, 4, 6, 9, ""}, - {2, 8, 6, 6, ""}, - {0, 0, 0, 0, ""}, - } - for _, tc := range testCases { - b := []byte("0123456789") - n := tc.dst1 - tc.dst0 - if tc.src1-tc.src0 < n { - n = tc.src1 - tc.src0 - } - forwardCopy(b, tc.dst0, tc.src0, n) - got := string(b[tc.dst0 : tc.dst0+n]) - if got != tc.want { - t.Errorf("dst=b[%d:%d], src=b[%d:%d]: got %q, want %q", - tc.dst0, tc.dst1, tc.src0, tc.src1, got, tc.want) - } - // Check that the bytes outside of dst[:n] were not modified. - for i, x := range b { - if i >= tc.dst0 && i < tc.dst0+n { - continue - } - if int(x) != '0'+i { - t.Errorf("dst=b[%d:%d], src=b[%d:%d]: copy overrun at b[%d]: got '%c', want '%c'", - tc.dst0, tc.dst1, tc.src0, tc.src1, i, x, '0'+i) - } - } - } -} diff --git a/src/compress/flate/dict_decoder.go b/src/compress/flate/dict_decoder.go new file mode 100644 index 0000000000..71c75a065e --- /dev/null +++ b/src/compress/flate/dict_decoder.go @@ -0,0 +1,184 @@ +// Copyright 2016 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package flate + +// dictDecoder implements the LZ77 sliding dictionary as used in decompression. +// LZ77 decompresses data through sequences of two forms of commands: +// +// * Literal insertions: Runs of one or more symbols are inserted into the data +// stream as is. This is accomplished through the writeByte method for a +// single symbol, or combinations of writeSlice/writeMark for multiple symbols. +// Any valid stream must start with a literal insertion if no preset dictionary +// is used. +// +// * Backward copies: Runs of one or more symbols are copied from previously +// emitted data. Backward copies come as the tuple (dist, length) where dist +// determines how far back in the stream to copy from and length determines how +// many bytes to copy. Note that it is valid for the length to be greater than +// the distance. Since LZ77 uses forward copies, that situation is used to +// perform a form of run-length encoding on repeated runs of symbols. +// The writeCopy and tryWriteCopy are used to implement this command. +// +// For performance reasons, this implementation performs little to no sanity +// checks about the arguments. As such, the invariants documented for each +// method call must be respected. +type dictDecoder struct { + hist []byte // Sliding window history + + // Invariant: 0 <= rdPos <= wrPos <= len(hist) + wrPos int // Current output position in buffer + rdPos int // Have emitted hist[:rdPos] already + full bool // Has a full window length been written yet? +} + +// init initializes dictDecoder to have a sliding window dictionary of the given +// size. If a preset dict is provided, it will initialize the dictionary with +// the contents of dict. +func (dd *dictDecoder) init(size int, dict []byte) { + *dd = dictDecoder{hist: dd.hist} + + if cap(dd.hist) < size { + dd.hist = make([]byte, size) + } + dd.hist = dd.hist[:size] + + if len(dict) > len(dd.hist) { + dict = dict[len(dict)-len(dd.hist):] + } + dd.wrPos = copy(dd.hist, dict) + if dd.wrPos == len(dd.hist) { + dd.wrPos = 0 + dd.full = true + } + dd.rdPos = dd.wrPos +} + +// histSize reports the total amount of historical data in the dictionary. +func (dd *dictDecoder) histSize() int { + if dd.full { + return len(dd.hist) + } + return dd.wrPos +} + +// availRead reports the number of bytes that can be flushed by readFlush. +func (dd *dictDecoder) availRead() int { + return dd.wrPos - dd.rdPos +} + +// availWrite reports the available amount of output buffer space. +func (dd *dictDecoder) availWrite() int { + return len(dd.hist) - dd.wrPos +} + +// writeSlice returns a slice of the available buffer to write data to. +// +// This invariant will be kept: len(s) <= availWrite() +func (dd *dictDecoder) writeSlice() []byte { + return dd.hist[dd.wrPos:] +} + +// writeMark advances the writer pointer by cnt. +// +// This invariant must be kept: 0 <= cnt <= availWrite() +func (dd *dictDecoder) writeMark(cnt int) { + dd.wrPos += cnt +} + +// writeByte writes a single byte to the dictionary. +// +// This invariant must be kept: 0 < availWrite() +func (dd *dictDecoder) writeByte(c byte) { + dd.hist[dd.wrPos] = c + dd.wrPos++ +} + +// writeCopy copies a string at a given (dist, length) to the output. +// This returns the number of bytes copied and may be less than the requested +// length if the available space in the output buffer is too small. +// +// This invariant must be kept: 0 < dist <= histSize() +func (dd *dictDecoder) writeCopy(dist, length int) int { + dstBase := dd.wrPos + dstPos := dstBase + srcPos := dstPos - dist + endPos := dstPos + length + if endPos > len(dd.hist) { + endPos = len(dd.hist) + } + + // Copy non-overlapping section after destination position. + // + // This section is non-overlapping in that the copy length for this section + // is always less than or equal to the backwards distance. This can occur + // if a distance refers to data that wraps-around in the buffer. + // Thus, a backwards copy is performed here; that is, the exact bytes in + // the source prior to the copy is placed in the destination. + if srcPos < 0 { + srcPos += len(dd.hist) + dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:]) + srcPos = 0 + } + + // Copy possibly overlapping section before destination position. + // + // This section can overlap if the copy length for this section is larger + // than the backwards distance. This is allowed by LZ77 so that repeated + // strings can be succinctly represented using (dist, length) pairs. + // Thus, a forwards copy is performed here; that is, the bytes copied is + // possibly dependent on the resulting bytes in the destination as the copy + // progresses along. This is functionally equivalent to the following: + // + // for i := 0; i < endPos-dstPos; i++ { + // dd.hist[dstPos+i] = dd.hist[srcPos+i] + // } + // dstPos = endPos + // + for dstPos < endPos { + dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:dstPos]) + } + + dd.wrPos = dstPos + return dstPos - dstBase +} + +// tryWriteCopy tries to copy a string at a given (distance, length) to the +// output. This specialized version is optimized for short distances. +// +// This method is designed to be inlined for performance reasons. +// +// This invariant must be kept: 0 < dist <= histSize() +func (dd *dictDecoder) tryWriteCopy(dist, length int) int { + dstPos := dd.wrPos + endPos := dstPos + length + if dstPos < dist || endPos > len(dd.hist) { + return 0 + } + dstBase := dstPos + srcPos := dstPos - dist + + // Copy possibly overlapping section before destination position. +loop: + dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:dstPos]) + if dstPos < endPos { + goto loop // Avoid for-loop so that this function can be inlined + } + + dd.wrPos = dstPos + return dstPos - dstBase +} + +// readFlush returns a slice of the historical buffer that is ready to be +// emitted to the user. The data returned by readFlush must be fully consumed +// before calling any other dictDecoder methods. +func (dd *dictDecoder) readFlush() []byte { + toRead := dd.hist[dd.rdPos:dd.wrPos] + dd.rdPos = dd.wrPos + if dd.wrPos == len(dd.hist) { + dd.wrPos, dd.rdPos = 0, 0 + dd.full = true + } + return toRead +} diff --git a/src/compress/flate/dict_decoder_test.go b/src/compress/flate/dict_decoder_test.go new file mode 100644 index 0000000000..9275cff791 --- /dev/null +++ b/src/compress/flate/dict_decoder_test.go @@ -0,0 +1,139 @@ +// Copyright 2016 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package flate + +import ( + "bytes" + "strings" + "testing" +) + +func TestDictDecoder(t *testing.T) { + const ( + abc = "ABC\n" + fox = "The quick brown fox jumped over the lazy dog!\n" + poem = "The Road Not Taken\nRobert Frost\n" + + "\n" + + "Two roads diverged in a yellow wood,\n" + + "And sorry I could not travel both\n" + + "And be one traveler, long I stood\n" + + "And looked down one as far as I could\n" + + "To where it bent in the undergrowth;\n" + + "\n" + + "Then took the other, as just as fair,\n" + + "And having perhaps the better claim,\n" + + "Because it was grassy and wanted wear;\n" + + "Though as for that the passing there\n" + + "Had worn them really about the same,\n" + + "\n" + + "And both that morning equally lay\n" + + "In leaves no step had trodden black.\n" + + "Oh, I kept the first for another day!\n" + + "Yet knowing how way leads on to way,\n" + + "I doubted if I should ever come back.\n" + + "\n" + + "I shall be telling this with a sigh\n" + + "Somewhere ages and ages hence:\n" + + "Two roads diverged in a wood, and I-\n" + + "I took the one less traveled by,\n" + + "And that has made all the difference.\n" + ) + + var poemRefs = []struct { + dist int // Backward distance (0 if this is an insertion) + length int // Length of copy or insertion + }{ + {0, 38}, {33, 3}, {0, 48}, {79, 3}, {0, 11}, {34, 5}, {0, 6}, {23, 7}, + {0, 8}, {50, 3}, {0, 2}, {69, 3}, {34, 5}, {0, 4}, {97, 3}, {0, 4}, + {43, 5}, {0, 6}, {7, 4}, {88, 7}, {0, 12}, {80, 3}, {0, 2}, {141, 4}, + {0, 1}, {196, 3}, {0, 3}, {157, 3}, {0, 6}, {181, 3}, {0, 2}, {23, 3}, + {77, 3}, {28, 5}, {128, 3}, {110, 4}, {70, 3}, {0, 4}, {85, 6}, {0, 2}, + {182, 6}, {0, 4}, {133, 3}, {0, 7}, {47, 5}, {0, 20}, {112, 5}, {0, 1}, + {58, 3}, {0, 8}, {59, 3}, {0, 4}, {173, 3}, {0, 5}, {114, 3}, {0, 4}, + {92, 5}, {0, 2}, {71, 3}, {0, 2}, {76, 5}, {0, 1}, {46, 3}, {96, 4}, + {130, 4}, {0, 3}, {360, 3}, {0, 3}, {178, 5}, {0, 7}, {75, 3}, {0, 3}, + {45, 6}, {0, 6}, {299, 6}, {180, 3}, {70, 6}, {0, 1}, {48, 3}, {66, 4}, + {0, 3}, {47, 5}, {0, 9}, {325, 3}, {0, 1}, {359, 3}, {318, 3}, {0, 2}, + {199, 3}, {0, 1}, {344, 3}, {0, 3}, {248, 3}, {0, 10}, {310, 3}, {0, 3}, + {93, 6}, {0, 3}, {252, 3}, {157, 4}, {0, 2}, {273, 5}, {0, 14}, {99, 4}, + {0, 1}, {464, 4}, {0, 2}, {92, 4}, {495, 3}, {0, 1}, {322, 4}, {16, 4}, + {0, 3}, {402, 3}, {0, 2}, {237, 4}, {0, 2}, {432, 4}, {0, 1}, {483, 5}, + {0, 2}, {294, 4}, {0, 2}, {306, 3}, {113, 5}, {0, 1}, {26, 4}, {164, 3}, + {488, 4}, {0, 1}, {542, 3}, {248, 6}, {0, 5}, {205, 3}, {0, 8}, {48, 3}, + {449, 6}, {0, 2}, {192, 3}, {328, 4}, {9, 5}, {433, 3}, {0, 3}, {622, 25}, + {615, 5}, {46, 5}, {0, 2}, {104, 3}, {475, 10}, {549, 3}, {0, 4}, {597, 8}, + {314, 3}, {0, 1}, {473, 6}, {317, 5}, {0, 1}, {400, 3}, {0, 3}, {109, 3}, + {151, 3}, {48, 4}, {0, 4}, {125, 3}, {108, 3}, {0, 2}, + } + + var got, want bytes.Buffer + var dd dictDecoder + dd.init(1<<11, nil) + + var writeCopy = func(dist, length int) { + for length > 0 { + cnt := dd.tryWriteCopy(dist, length) + if cnt == 0 { + cnt = dd.writeCopy(dist, length) + } + + length -= cnt + if dd.availWrite() == 0 { + got.Write(dd.readFlush()) + } + } + } + var writeString = func(str string) { + for len(str) > 0 { + cnt := copy(dd.writeSlice(), str) + str = str[cnt:] + dd.writeMark(cnt) + if dd.availWrite() == 0 { + got.Write(dd.readFlush()) + } + } + } + + writeString(".") + want.WriteByte('.') + + str := poem + for _, ref := range poemRefs { + if ref.dist == 0 { + writeString(str[:ref.length]) + } else { + writeCopy(ref.dist, ref.length) + } + str = str[ref.length:] + } + want.WriteString(poem) + + writeCopy(dd.histSize(), 33) + want.Write(want.Bytes()[:33]) + + writeString(abc) + writeCopy(len(abc), 59*len(abc)) + want.WriteString(strings.Repeat(abc, 60)) + + writeString(fox) + writeCopy(len(fox), 9*len(fox)) + want.WriteString(strings.Repeat(fox, 10)) + + writeString(".") + writeCopy(1, 9) + want.WriteString(strings.Repeat(".", 10)) + + writeString(strings.ToUpper(poem)) + writeCopy(len(poem), 7*len(poem)) + want.WriteString(strings.Repeat(strings.ToUpper(poem), 8)) + + writeCopy(dd.histSize(), 10) + want.Write(want.Bytes()[want.Len()-dd.histSize():][:10]) + + got.Write(dd.readFlush()) + if got.String() != want.String() { + t.Errorf("final string mismatch:\ngot %q\nwant %q", got.String(), want.String()) + } +} diff --git a/src/compress/flate/inflate.go b/src/compress/flate/inflate.go index 42261e9b61..dccfdf2288 100644 --- a/src/compress/flate/inflate.go +++ b/src/compress/flate/inflate.go @@ -282,29 +282,28 @@ type decompressor struct { codebits *[numCodes]int // Output history, buffer. - hist *[maxHist]byte - hp int // current output position in buffer - hw int // have written hist[0:hw] already - hfull bool // buffer has filled at least once + dict dictDecoder // Temporary buffer (avoids repeated allocation). buf [4]byte // Next step in the decompression, // and decompression state. - step func(*decompressor) - final bool - err error - toRead []byte - hl, hd *huffmanDecoder - copyLen int - copyDist int + step func(*decompressor) + stepState int + final bool + err error + toRead []byte + hl, hd *huffmanDecoder + copyLen int + copyDist int } func (f *decompressor) nextBlock() { if f.final { - if f.hw != f.hp { - f.flush((*decompressor).nextBlock) + if f.dict.availRead() > 0 { + f.toRead = f.dict.readFlush() + f.step = (*decompressor).nextBlock return } f.err = io.EOF @@ -353,6 +352,7 @@ func (f *decompressor) Read(b []byte) (int, error) { return 0, f.err } f.step(f) + f.woffset += int64(len(f.toRead)) } } @@ -481,7 +481,21 @@ func (f *decompressor) readHuffman() error { // and the distance values, respectively. If hd == nil, using the // fixed distance encoding associated with fixed Huffman blocks. func (f *decompressor) huffmanBlock() { - for { + const ( + stateInit = iota // Zero value must be stateInit + stateDict + ) + + switch f.stepState { + case stateInit: + goto readLiteral + case stateDict: + goto copyHistory + } + +readLiteral: + // Read literal and/or (length, distance) according to RFC section 3.2.3. + { v, err := f.huffSym(f.hl) if err != nil { f.err = err @@ -491,14 +505,14 @@ func (f *decompressor) huffmanBlock() { var length int switch { case v < 256: - f.hist[f.hp] = byte(v) - f.hp++ - if f.hp == len(f.hist) { - // After the flush, continue this loop. - f.flush((*decompressor).huffmanBlock) + f.dict.writeByte(byte(v)) + if f.dict.availWrite() == 0 { + f.toRead = f.dict.readFlush() + f.step = (*decompressor).huffmanBlock + f.stepState = stateInit return } - continue + goto readLiteral case v == 256: // Done with huffman block; read next block. f.step = (*decompressor).nextBlock @@ -581,63 +595,35 @@ func (f *decompressor) huffmanBlock() { return } - // Copy history[-dist:-dist+length] into output. - if dist > len(f.hist) { - f.err = InternalError("bad history distance") - return - } - // No check on length; encoding can be prescient. - if !f.hfull && dist > f.hp { + if dist > f.dict.histSize() { f.err = CorruptInputError(f.roffset) return } f.copyLen, f.copyDist = length, dist - if f.copyHist() { + goto copyHistory + } + +copyHistory: + // Perform a backwards copy according to RFC section 3.2.3. + { + cnt := f.dict.tryWriteCopy(f.copyDist, f.copyLen) + if cnt == 0 { + cnt = f.dict.writeCopy(f.copyDist, f.copyLen) + } + f.copyLen -= cnt + + if f.dict.availWrite() == 0 || f.copyLen > 0 { + f.toRead = f.dict.readFlush() + f.step = (*decompressor).huffmanBlock // We need to continue this work + f.stepState = stateDict return } + goto readLiteral } } -// copyHist copies f.copyLen bytes from f.hist (f.copyDist bytes ago) to itself. -// It reports whether the f.hist buffer is full. -func (f *decompressor) copyHist() bool { - p := f.hp - f.copyDist - if p < 0 { - p += len(f.hist) - } - for f.copyLen > 0 { - n := f.copyLen - if x := len(f.hist) - f.hp; n > x { - n = x - } - if x := len(f.hist) - p; n > x { - n = x - } - forwardCopy(f.hist[:], f.hp, p, n) - p += n - f.hp += n - f.copyLen -= n - if f.hp == len(f.hist) { - // After flush continue copying out of history. - f.flush((*decompressor).copyHuff) - return true - } - if p == len(f.hist) { - p = 0 - } - } - return false -} - -func (f *decompressor) copyHuff() { - if f.copyHist() { - return - } - f.huffmanBlock() -} - // Copy a single uncompressed data block from input to output. func (f *decompressor) dataBlock() { // Uncompressed. @@ -663,8 +649,8 @@ func (f *decompressor) dataBlock() { } if n == 0 { - // 0-length block means sync - f.flush((*decompressor).nextBlock) + f.toRead = f.dict.readFlush() + f.step = (*decompressor).nextBlock return } @@ -675,46 +661,31 @@ func (f *decompressor) dataBlock() { // copyData copies f.copyLen bytes from the underlying reader into f.hist. // It pauses for reads when f.hist is full. func (f *decompressor) copyData() { - n := f.copyLen - for n > 0 { - m := len(f.hist) - f.hp - if m > n { - m = n - } - m, err := io.ReadFull(f.r, f.hist[f.hp:f.hp+m]) - f.roffset += int64(m) - if err != nil { - if err == io.EOF { - err = io.ErrUnexpectedEOF - } - f.err = err - return - } - n -= m - f.hp += m - if f.hp == len(f.hist) { - f.copyLen = n - f.flush((*decompressor).copyData) - return + buf := f.dict.writeSlice() + if len(buf) > f.copyLen { + buf = buf[:f.copyLen] + } + + cnt, err := io.ReadFull(f.r, buf) + f.roffset += int64(cnt) + f.copyLen -= cnt + f.dict.writeMark(cnt) + if err != nil { + if err == io.EOF { + err = io.ErrUnexpectedEOF } + f.err = err + return + } + + if f.dict.availWrite() == 0 || f.copyLen > 0 { + f.toRead = f.dict.readFlush() + f.step = (*decompressor).copyData + return } f.step = (*decompressor).nextBlock } -func (f *decompressor) setDict(dict []byte) { - if len(dict) > len(f.hist) { - // Will only remember the tail. - dict = dict[len(dict)-len(f.hist):] - } - - f.hp = copy(f.hist[:], dict) - if f.hp == len(f.hist) { - f.hp = 0 - f.hfull = true - } - f.hw = f.hp -} - func (f *decompressor) moreBits() error { c, err := f.r.ReadByte() if err != nil { @@ -760,19 +731,6 @@ func (f *decompressor) huffSym(h *huffmanDecoder) (int, error) { } } -// Flush any buffered output to the underlying writer. -func (f *decompressor) flush(step func(*decompressor)) { - f.toRead = f.hist[f.hw:f.hp] - f.woffset += int64(f.hp - f.hw) - f.hw = f.hp - if f.hp == len(f.hist) { - f.hp = 0 - f.hw = 0 - f.hfull = true - } - f.step = step -} - func makeReader(r io.Reader) Reader { if rr, ok := r.(Reader); ok { return rr @@ -805,12 +763,10 @@ func (f *decompressor) Reset(r io.Reader, dict []byte) error { r: makeReader(r), bits: f.bits, codebits: f.codebits, - hist: f.hist, + dict: f.dict, step: (*decompressor).nextBlock, } - if dict != nil { - f.setDict(dict) - } + f.dict.init(maxHist, nil) return nil } @@ -827,10 +783,10 @@ func NewReader(r io.Reader) io.ReadCloser { var f decompressor f.r = makeReader(r) - f.hist = new([maxHist]byte) f.bits = new([maxNumLit + maxNumDist]int) f.codebits = new([numCodes]int) f.step = (*decompressor).nextBlock + f.dict.init(maxHist, nil) return &f } @@ -846,10 +802,9 @@ func NewReaderDict(r io.Reader, dict []byte) io.ReadCloser { var f decompressor f.r = makeReader(r) - f.hist = new([maxHist]byte) f.bits = new([maxNumLit + maxNumDist]int) f.codebits = new([numCodes]int) f.step = (*decompressor).nextBlock - f.setDict(dict) + f.dict.init(maxHist, dict) return &f }