diff options
Diffstat (limited to 'Godeps/_workspace/src/golang.org/x/image/tiff/lzw')
-rw-r--r-- | Godeps/_workspace/src/golang.org/x/image/tiff/lzw/reader.go | 277 |
1 files changed, 0 insertions, 277 deletions
diff --git a/Godeps/_workspace/src/golang.org/x/image/tiff/lzw/reader.go b/Godeps/_workspace/src/golang.org/x/image/tiff/lzw/reader.go deleted file mode 100644 index dc9f7dd1d..000000000 --- a/Godeps/_workspace/src/golang.org/x/image/tiff/lzw/reader.go +++ /dev/null @@ -1,277 +0,0 @@ -// Copyright 2011 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 lzw implements the Lempel-Ziv-Welch compressed data format, -// described in T. A. Welch, ``A Technique for High-Performance Data -// Compression'', Computer, 17(6) (June 1984), pp 8-19. -// -// In particular, it implements LZW as used by the TIFF file format, including -// an "off by one" algorithmic difference when compared to standard LZW. -package lzw - -/* -This file was branched from src/pkg/compress/lzw/reader.go in the -standard library. Differences from the original are marked with "NOTE". - -The tif_lzw.c file in the libtiff C library has this comment: - ----- -The 5.0 spec describes a different algorithm than Aldus -implements. Specifically, Aldus does code length transitions -one code earlier than should be done (for real LZW). -Earlier versions of this library implemented the correct -LZW algorithm, but emitted codes in a bit order opposite -to the TIFF spec. Thus, to maintain compatibility w/ Aldus -we interpret MSB-LSB ordered codes to be images written w/ -old versions of this library, but otherwise adhere to the -Aldus "off by one" algorithm. ----- - -The Go code doesn't read (invalid) TIFF files written by old versions of -libtiff, but the LZW algorithm in this package still differs from the one in -Go's standard package library to accomodate this "off by one" in valid TIFFs. -*/ - -import ( - "bufio" - "errors" - "fmt" - "io" -) - -// Order specifies the bit ordering in an LZW data stream. -type Order int - -const ( - // LSB means Least Significant Bits first, as used in the GIF file format. - LSB Order = iota - // MSB means Most Significant Bits first, as used in the TIFF and PDF - // file formats. - MSB -) - -const ( - maxWidth = 12 - decoderInvalidCode = 0xffff - flushBuffer = 1 << maxWidth -) - -// decoder is the state from which the readXxx method converts a byte -// stream into a code stream. -type decoder struct { - r io.ByteReader - bits uint32 - nBits uint - width uint - read func(*decoder) (uint16, error) // readLSB or readMSB - litWidth int // width in bits of literal codes - err error - - // The first 1<<litWidth codes are literal codes. - // The next two codes mean clear and EOF. - // Other valid codes are in the range [lo, hi] where lo := clear + 2, - // with the upper bound incrementing on each code seen. - // overflow is the code at which hi overflows the code width. NOTE: TIFF's LZW is "off by one". - // last is the most recently seen code, or decoderInvalidCode. - clear, eof, hi, overflow, last uint16 - - // Each code c in [lo, hi] expands to two or more bytes. For c != hi: - // suffix[c] is the last of these bytes. - // prefix[c] is the code for all but the last byte. - // This code can either be a literal code or another code in [lo, c). - // The c == hi case is a special case. - suffix [1 << maxWidth]uint8 - prefix [1 << maxWidth]uint16 - - // output is the temporary output buffer. - // Literal codes are accumulated from the start of the buffer. - // Non-literal codes decode to a sequence of suffixes that are first - // written right-to-left from the end of the buffer before being copied - // to the start of the buffer. - // It is flushed when it contains >= 1<<maxWidth bytes, - // so that there is always room to decode an entire code. - output [2 * 1 << maxWidth]byte - o int // write index into output - toRead []byte // bytes to return from Read -} - -// readLSB returns the next code for "Least Significant Bits first" data. -func (d *decoder) readLSB() (uint16, error) { - for d.nBits < d.width { - x, err := d.r.ReadByte() - if err != nil { - return 0, err - } - d.bits |= uint32(x) << d.nBits - d.nBits += 8 - } - code := uint16(d.bits & (1<<d.width - 1)) - d.bits >>= d.width - d.nBits -= d.width - return code, nil -} - -// readMSB returns the next code for "Most Significant Bits first" data. -func (d *decoder) readMSB() (uint16, error) { - for d.nBits < d.width { - x, err := d.r.ReadByte() - if err != nil { - return 0, err - } - d.bits |= uint32(x) << (24 - d.nBits) - d.nBits += 8 - } - code := uint16(d.bits >> (32 - d.width)) - d.bits <<= d.width - d.nBits -= d.width - return code, nil -} - -func (d *decoder) Read(b []byte) (int, error) { - for { - if len(d.toRead) > 0 { - n := copy(b, d.toRead) - d.toRead = d.toRead[n:] - return n, nil - } - if d.err != nil { - return 0, d.err - } - d.decode() - } -} - -// decode decompresses bytes from r and leaves them in d.toRead. -// read specifies how to decode bytes into codes. -// litWidth is the width in bits of literal codes. -func (d *decoder) decode() { - // Loop over the code stream, converting codes into decompressed bytes. - for { - code, err := d.read(d) - if err != nil { - if err == io.EOF { - err = io.ErrUnexpectedEOF - } - d.err = err - d.flush() - return - } - switch { - case code < d.clear: - // We have a literal code. - d.output[d.o] = uint8(code) - d.o++ - if d.last != decoderInvalidCode { - // Save what the hi code expands to. - d.suffix[d.hi] = uint8(code) - d.prefix[d.hi] = d.last - } - case code == d.clear: - d.width = 1 + uint(d.litWidth) - d.hi = d.eof - d.overflow = 1 << d.width - d.last = decoderInvalidCode - continue - case code == d.eof: - d.flush() - d.err = io.EOF - return - case code <= d.hi: - c, i := code, len(d.output)-1 - if code == d.hi { - // code == hi is a special case which expands to the last expansion - // followed by the head of the last expansion. To find the head, we walk - // the prefix chain until we find a literal code. - c = d.last - for c >= d.clear { - c = d.prefix[c] - } - d.output[i] = uint8(c) - i-- - c = d.last - } - // Copy the suffix chain into output and then write that to w. - for c >= d.clear { - d.output[i] = d.suffix[c] - i-- - c = d.prefix[c] - } - d.output[i] = uint8(c) - d.o += copy(d.output[d.o:], d.output[i:]) - if d.last != decoderInvalidCode { - // Save what the hi code expands to. - d.suffix[d.hi] = uint8(c) - d.prefix[d.hi] = d.last - } - default: - d.err = errors.New("lzw: invalid code") - d.flush() - return - } - d.last, d.hi = code, d.hi+1 - if d.hi+1 >= d.overflow { // NOTE: the "+1" is where TIFF's LZW differs from the standard algorithm. - if d.width == maxWidth { - d.last = decoderInvalidCode - } else { - d.width++ - d.overflow <<= 1 - } - } - if d.o >= flushBuffer { - d.flush() - return - } - } -} - -func (d *decoder) flush() { - d.toRead = d.output[:d.o] - d.o = 0 -} - -var errClosed = errors.New("lzw: reader/writer is closed") - -func (d *decoder) Close() error { - d.err = errClosed // in case any Reads come along - return nil -} - -// NewReader creates a new io.ReadCloser. -// Reads from the returned io.ReadCloser read and decompress data from r. -// If r does not also implement io.ByteReader, -// the decompressor may read more data than necessary from r. -// It is the caller's responsibility to call Close on the ReadCloser when -// finished reading. -// The number of bits to use for literal codes, litWidth, must be in the -// range [2,8] and is typically 8. It must equal the litWidth -// used during compression. -func NewReader(r io.Reader, order Order, litWidth int) io.ReadCloser { - d := new(decoder) - switch order { - case LSB: - d.read = (*decoder).readLSB - case MSB: - d.read = (*decoder).readMSB - default: - d.err = errors.New("lzw: unknown order") - return d - } - if litWidth < 2 || 8 < litWidth { - d.err = fmt.Errorf("lzw: litWidth %d out of range", litWidth) - return d - } - if br, ok := r.(io.ByteReader); ok { - d.r = br - } else { - d.r = bufio.NewReader(r) - } - d.litWidth = litWidth - d.width = 1 + uint(litWidth) - d.clear = uint16(1) << uint(litWidth) - d.eof, d.hi = d.clear+1, d.clear+1 - d.overflow = uint16(1) << d.width - d.last = decoderInvalidCode - - return d -} |