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authorbaude <bbaude@redhat.com>2019-01-03 08:55:35 -0600
committerbaude <bbaude@redhat.com>2019-01-03 12:49:30 -0600
commit561e65969f89c6f60193cf1755752b571a1149f5 (patch)
tree8f2f784c27546f061a38cf5fe68a9ee672be950f /vendor/github.com/klauspost/compress/flate/dict_decoder.go
parent098c13418abf3985f20689bdda0361904a40ef98 (diff)
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vendor in new containers/storage
vendor in latest containers/storage which contains a fix for when a filesystem that overlayfs is on is ENOSPC. adding pgzip/compress as a new dep for c/s Signed-off-by: baude <bbaude@redhat.com>
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+// 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
+}