Imported Upstream version 60upstream/60

1 files changed, 493 insertions, 0 deletions

diff --git a/src/pkg/compress/flate/deflate.go b/src/pkg/compress/flate/deflate.go
new file mode 100644
index 000000000..b1cee0b2f
--- /dev/null
+++ b/src/pkg/compress/flate/deflate.go
@@ -0,0 +1,493 @@
+// Copyright 2009 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 (
+	"io"
+	"math"
+	"os"
+)
+
+const (
+	NoCompression      = 0
+	BestSpeed          = 1
+	fastCompression    = 3
+	BestCompression    = 9
+	DefaultCompression = -1
+	logWindowSize      = 15
+	windowSize         = 1 << logWindowSize
+	windowMask         = windowSize - 1
+	logMaxOffsetSize   = 15  // Standard DEFLATE
+	minMatchLength     = 3   // The smallest match that the compressor looks for
+	maxMatchLength     = 258 // The longest match for the compressor
+	minOffsetSize      = 1   // The shortest offset that makes any sence
+
+	// The maximum number of tokens we put into a single flat block, just too
+	// stop things from getting too large.
+	maxFlateBlockTokens = 1 << 14
+	maxStoreBlockSize   = 65535
+	hashBits            = 15
+	hashSize            = 1 << hashBits
+	hashMask            = (1 << hashBits) - 1
+	hashShift           = (hashBits + minMatchLength - 1) / minMatchLength
+)
+
+type compressionLevel struct {
+	good, lazy, nice, chain, fastSkipHashing int
+}
+
+var levels = []compressionLevel{
+	{}, // 0
+	// For levels 1-3 we don't bother trying with lazy matches
+	{3, 0, 8, 4, 4},
+	{3, 0, 16, 8, 5},
+	{3, 0, 32, 32, 6},
+	// Levels 4-9 use increasingly more lazy matching
+	// and increasingly stringent conditions for "good enough".
+	{4, 4, 16, 16, math.MaxInt32},
+	{8, 16, 32, 32, math.MaxInt32},
+	{8, 16, 128, 128, math.MaxInt32},
+	{8, 32, 128, 256, math.MaxInt32},
+	{32, 128, 258, 1024, math.MaxInt32},
+	{32, 258, 258, 4096, math.MaxInt32},
+}
+
+type compressor struct {
+	compressionLevel
+
+	w *huffmanBitWriter
+
+	// compression algorithm
+	fill func(*compressor, []byte) int // copy data to window
+	step func(*compressor)             // process window
+	sync bool                          // requesting flush
+
+	// Input hash chains
+	// hashHead[hashValue] contains the largest inputIndex with the specified hash value
+	// If hashHead[hashValue] is within the current window, then
+	// hashPrev[hashHead[hashValue] & windowMask] contains the previous index
+	// with the same hash value.
+	chainHead int
+	hashHead  []int
+	hashPrev  []int
+
+	// input window: unprocessed data is window[index:windowEnd]
+	index         int
+	window        []byte
+	windowEnd     int
+	blockStart    int  // window index where current tokens start
+	byteAvailable bool // if true, still need to process window[index-1].
+
+	// queued output tokens: tokens[:ti]
+	tokens []token
+	ti     int
+
+	// deflate state
+	length         int
+	offset         int
+	hash           int
+	maxInsertIndex int
+	err            os.Error
+}
+
+func (d *compressor) fillDeflate(b []byte) int {
+	if d.index >= 2*windowSize-(minMatchLength+maxMatchLength) {
+		// shift the window by windowSize
+		copy(d.window, d.window[windowSize:2*windowSize])
+		d.index -= windowSize
+		d.windowEnd -= windowSize
+		if d.blockStart >= windowSize {
+			d.blockStart -= windowSize
+		} else {
+			d.blockStart = math.MaxInt32
+		}
+		for i, h := range d.hashHead {
+			v := h - windowSize
+			if v < -1 {
+				v = -1
+			}
+			d.hashHead[i] = v
+		}
+		for i, h := range d.hashPrev {
+			v := -h - windowSize
+			if v < -1 {
+				v = -1
+			}
+			d.hashPrev[i] = v
+		}
+	}
+	n := copy(d.window[d.windowEnd:], b)
+	d.windowEnd += n
+	return n
+}
+
+func (d *compressor) writeBlock(tokens []token, index int, eof bool) os.Error {
+	if index > 0 || eof {
+		var window []byte
+		if d.blockStart <= index {
+			window = d.window[d.blockStart:index]
+		}
+		d.blockStart = index
+		d.w.writeBlock(tokens, eof, window)
+		return d.w.err
+	}
+	return nil
+}
+
+// Try to find a match starting at index whose length is greater than prevSize.
+// We only look at chainCount possibilities before giving up.
+func (d *compressor) findMatch(pos int, prevHead int, prevLength int, lookahead int) (length, offset int, ok bool) {
+	minMatchLook := maxMatchLength
+	if lookahead < minMatchLook {
+		minMatchLook = lookahead
+	}
+
+	win := d.window[0 : pos+minMatchLook]
+
+	// We quit when we get a match that's at least nice long
+	nice := len(win) - pos
+	if d.nice < nice {
+		nice = d.nice
+	}
+
+	// If we've got a match that's good enough, only look in 1/4 the chain.
+	tries := d.chain
+	length = prevLength
+	if length >= d.good {
+		tries >>= 2
+	}
+
+	w0 := win[pos]
+	w1 := win[pos+1]
+	wEnd := win[pos+length]
+	minIndex := pos - windowSize
+
+	for i := prevHead; tries > 0; tries-- {
+		if w0 == win[i] && w1 == win[i+1] && wEnd == win[i+length] {
+			// The hash function ensures that if win[i] and win[i+1] match, win[i+2] matches
+
+			n := 3
+			for pos+n < len(win) && win[i+n] == win[pos+n] {
+				n++
+			}
+			if n > length && (n > 3 || pos-i <= 4096) {
+				length = n
+				offset = pos - i
+				ok = true
+				if n >= nice {
+					// The match is good enough that we don't try to find a better one.
+					break
+				}
+				wEnd = win[pos+n]
+			}
+		}
+		if i == minIndex {
+			// hashPrev[i & windowMask] has already been overwritten, so stop now.
+			break
+		}
+		if i = d.hashPrev[i&windowMask]; i < minIndex || i < 0 {
+			break
+		}
+	}
+	return
+}
+
+func (d *compressor) writeStoredBlock(buf []byte) os.Error {
+	if d.w.writeStoredHeader(len(buf), false); d.w.err != nil {
+		return d.w.err
+	}
+	d.w.writeBytes(buf)
+	return d.w.err
+}
+
+func (d *compressor) initDeflate() {
+	d.hashHead = make([]int, hashSize)
+	d.hashPrev = make([]int, windowSize)
+	d.window = make([]byte, 2*windowSize)
+	fillInts(d.hashHead, -1)
+	d.tokens = make([]token, maxFlateBlockTokens, maxFlateBlockTokens+1)
+	d.length = minMatchLength - 1
+	d.offset = 0
+	d.byteAvailable = false
+	d.index = 0
+	d.ti = 0
+	d.hash = 0
+	d.chainHead = -1
+}
+
+func (d *compressor) deflate() {
+	if d.windowEnd-d.index < minMatchLength+maxMatchLength && !d.sync {
+		return
+	}
+
+	d.maxInsertIndex = d.windowEnd - (minMatchLength - 1)
+	if d.index < d.maxInsertIndex {
+		d.hash = int(d.window[d.index])<<hashShift + int(d.window[d.index+1])
+	}
+
+Loop:
+	for {
+		if d.index > d.windowEnd {
+			panic("index > windowEnd")
+		}
+		lookahead := d.windowEnd - d.index
+		if lookahead < minMatchLength+maxMatchLength {
+			if !d.sync {
+				break Loop
+			}
+			if d.index > d.windowEnd {
+				panic("index > windowEnd")
+			}
+			if lookahead == 0 {
+				// Flush current output block if any.
+				if d.byteAvailable {
+					// There is still one pending token that needs to be flushed
+					d.tokens[d.ti] = literalToken(uint32(d.window[d.index-1]))
+					d.ti++
+					d.byteAvailable = false
+				}
+				if d.ti > 0 {
+					if d.err = d.writeBlock(d.tokens[0:d.ti], d.index, false); d.err != nil {
+						return
+					}
+					d.ti = 0
+				}
+				break Loop
+			}
+		}
+		if d.index < d.maxInsertIndex {
+			// Update the hash
+			d.hash = (d.hash<<hashShift + int(d.window[d.index+2])) & hashMask
+			d.chainHead = d.hashHead[d.hash]
+			d.hashPrev[d.index&windowMask] = d.chainHead
+			d.hashHead[d.hash] = d.index
+		}
+		prevLength := d.length
+		prevOffset := d.offset
+		d.length = minMatchLength - 1
+		d.offset = 0
+		minIndex := d.index - windowSize
+		if minIndex < 0 {
+			minIndex = 0
+		}
+
+		if d.chainHead >= minIndex &&
+			(d.fastSkipHashing != 0 && lookahead > minMatchLength-1 ||
+				d.fastSkipHashing == 0 && lookahead > prevLength && prevLength < d.lazy) {
+			if newLength, newOffset, ok := d.findMatch(d.index, d.chainHead, minMatchLength-1, lookahead); ok {
+				d.length = newLength
+				d.offset = newOffset
+			}
+		}
+		if d.fastSkipHashing != 0 && d.length >= minMatchLength ||
+			d.fastSkipHashing == 0 && prevLength >= minMatchLength && d.length <= prevLength {
+			// There was a match at the previous step, and the current match is
+			// not better. Output the previous match.
+			if d.fastSkipHashing != 0 {
+				d.tokens[d.ti] = matchToken(uint32(d.length-minMatchLength), uint32(d.offset-minOffsetSize))
+			} else {
+				d.tokens[d.ti] = matchToken(uint32(prevLength-minMatchLength), uint32(prevOffset-minOffsetSize))
+			}
+			d.ti++
+			// Insert in the hash table all strings up to the end of the match.
+			// index and index-1 are already inserted. If there is not enough
+			// lookahead, the last two strings are not inserted into the hash
+			// table.
+			if d.length <= d.fastSkipHashing {
+				var newIndex int
+				if d.fastSkipHashing != 0 {
+					newIndex = d.index + d.length
+				} else {
+					newIndex = prevLength - 1
+				}
+				for d.index++; d.index < newIndex; d.index++ {
+					if d.index < d.maxInsertIndex {
+						d.hash = (d.hash<<hashShift + int(d.window[d.index+2])) & hashMask
+						// Get previous value with the same hash.
+						// Our chain should point to the previous value.
+						d.hashPrev[d.index&windowMask] = d.hashHead[d.hash]
+						// Set the head of the hash chain to us.
+						d.hashHead[d.hash] = d.index
+					}
+				}
+				if d.fastSkipHashing == 0 {
+					d.byteAvailable = false
+					d.length = minMatchLength - 1
+				}
+			} else {
+				// For matches this long, we don't bother inserting each individual
+				// item into the table.
+				d.index += d.length
+				d.hash = (int(d.window[d.index])<<hashShift + int(d.window[d.index+1]))
+			}
+			if d.ti == maxFlateBlockTokens {
+				// The block includes the current character
+				if d.err = d.writeBlock(d.tokens, d.index, false); d.err != nil {
+					return
+				}
+				d.ti = 0
+			}
+		} else {
+			if d.fastSkipHashing != 0 || d.byteAvailable {
+				i := d.index - 1
+				if d.fastSkipHashing != 0 {
+					i = d.index
+				}
+				d.tokens[d.ti] = literalToken(uint32(d.window[i]))
+				d.ti++
+				if d.ti == maxFlateBlockTokens {
+					if d.err = d.writeBlock(d.tokens, i+1, false); d.err != nil {
+						return
+					}
+					d.ti = 0
+				}
+			}
+			d.index++
+			if d.fastSkipHashing == 0 {
+				d.byteAvailable = true
+			}
+		}
+	}
+}
+
+func (d *compressor) fillStore(b []byte) int {
+	n := copy(d.window[d.windowEnd:], b)
+	d.windowEnd += n
+	return n
+}
+
+func (d *compressor) store() {
+	if d.windowEnd > 0 {
+		d.err = d.writeStoredBlock(d.window[:d.windowEnd])
+	}
+	d.windowEnd = 0
+}
+
+func (d *compressor) write(b []byte) (n int, err os.Error) {
+	n = len(b)
+	b = b[d.fill(d, b):]
+	for len(b) > 0 {
+		d.step(d)
+		b = b[d.fill(d, b):]
+	}
+	return n, d.err
+}
+
+func (d *compressor) syncFlush() os.Error {
+	d.sync = true
+	d.step(d)
+	if d.err == nil {
+		d.w.writeStoredHeader(0, false)
+		d.w.flush()
+		d.err = d.w.err
+	}
+	d.sync = false
+	return d.err
+}
+
+func (d *compressor) init(w io.Writer, level int) (err os.Error) {
+	d.w = newHuffmanBitWriter(w)
+
+	switch {
+	case level == NoCompression:
+		d.window = make([]byte, maxStoreBlockSize)
+		d.fill = (*compressor).fillStore
+		d.step = (*compressor).store
+	case level == DefaultCompression:
+		level = 6
+		fallthrough
+	case 1 <= level && level <= 9:
+		d.compressionLevel = levels[level]
+		d.initDeflate()
+		d.fill = (*compressor).fillDeflate
+		d.step = (*compressor).deflate
+	default:
+		return WrongValueError{"level", 0, 9, int32(level)}
+	}
+	return nil
+}
+
+func (d *compressor) close() os.Error {
+	d.sync = true
+	d.step(d)
+	if d.err != nil {
+		return d.err
+	}
+	if d.w.writeStoredHeader(0, true); d.w.err != nil {
+		return d.w.err
+	}
+	d.w.flush()
+	return d.w.err
+}
+
+// NewWriter returns a new Writer compressing
+// data at the given level.  Following zlib, levels
+// range from 1 (BestSpeed) to 9 (BestCompression);
+// higher levels typically run slower but compress more.
+// Level 0 (NoCompression) does not attempt any
+// compression; it only adds the necessary DEFLATE framing.
+func NewWriter(w io.Writer, level int) *Writer {
+	const logWindowSize = logMaxOffsetSize
+	var dw Writer
+	dw.d.init(w, level)
+	return &dw
+}
+
+// NewWriterDict is like NewWriter but initializes the new
+// Writer with a preset dictionary.  The returned Writer behaves
+// as if the dictionary had been written to it without producing
+// any compressed output.  The compressed data written to w
+// can only be decompressed by a Reader initialized with the
+// same dictionary.
+func NewWriterDict(w io.Writer, level int, dict []byte) *Writer {
+	dw := &dictWriter{w, false}
+	zw := NewWriter(dw, level)
+	zw.Write(dict)
+	zw.Flush()
+	dw.enabled = true
+	return zw
+}
+
+type dictWriter struct {
+	w       io.Writer
+	enabled bool
+}
+
+func (w *dictWriter) Write(b []byte) (n int, err os.Error) {
+	if w.enabled {
+		return w.w.Write(b)
+	}
+	return len(b), nil
+}
+
+// A Writer takes data written to it and writes the compressed
+// form of that data to an underlying writer (see NewWriter).
+type Writer struct {
+	d compressor
+}
+
+// Write writes data to w, which will eventually write the
+// compressed form of data to its underlying writer.
+func (w *Writer) Write(data []byte) (n int, err os.Error) {
+	return w.d.write(data)
+}
+
+// Flush flushes any pending compressed data to the underlying writer.
+// It is useful mainly in compressed network protocols, to ensure that
+// a remote reader has enough data to reconstruct a packet.
+// Flush does not return until the data has been written.
+// If the underlying writer returns an error, Flush returns that error.
+//
+// In the terminology of the zlib library, Flush is equivalent to Z_SYNC_FLUSH.
+func (w *Writer) Flush() os.Error {
+	// For more about flushing:
+	// http://www.bolet.org/~pornin/deflate-flush.html
+	return w.d.syncFlush()
+}
+
+// Close flushes and closes the writer.
+func (w *Writer) Close() os.Error {
+	return w.d.close()
+}