diff options
Diffstat (limited to 'vendor/github.com/klauspost/compress/flate/dict_decoder.go')
| -rw-r--r-- | vendor/github.com/klauspost/compress/flate/dict_decoder.go | 184 |
1 files changed, 0 insertions, 184 deletions
diff --git a/vendor/github.com/klauspost/compress/flate/dict_decoder.go b/vendor/github.com/klauspost/compress/flate/dict_decoder.go deleted file mode 100644 index 71c75a06..00000000 --- a/vendor/github.com/klauspost/compress/flate/dict_decoder.go +++ /dev/null @@ -1,184 +0,0 @@ -// 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 -} |