forgejo/vendor/github.com/ulikunitz/xz/TODO.md

TODO list

Release v0.5.x

1. Support check flag in gxz command.

Release v0.6

1. Review encoder and check for lzma improvements under xz.
2. Fix binary tree matcher.
3. Compare compression ratio with xz tool using comparable parameters and optimize parameters
4. rename operation action and make it a simple type of size 8
5. make maxMatches, wordSize parameters
6. stop searching after a certain length is found (parameter sweetLen)

Release v0.7

1. Optimize code
2. Do statistical analysis to get linear presets.
3. Test sync.Pool compatability for xz and lzma Writer and Reader
4. Fuzz optimized code.

Release v0.8

1. Support parallel go routines for writing and reading xz files.
2. Support a ReaderAt interface for xz files with small block sizes.
3. Improve compatibility between gxz and xz
4. Provide manual page for gxz

Release v0.9

1. Improve documentation
2. Fuzz again

Release v1.0

1. Full functioning gxz
2. Add godoc URL to README.md (godoc.org)
3. Resolve all issues.
4. Define release candidates.
5. Public announcement.

Package lzma

v0.6

• Rewrite Encoder into a simple greedy one-op-at-a-time encoder including
  • simple scan at the dictionary head for the same byte
  • use the killer byte (requiring matches to get longer, the first test should be the byte that would make the match longer)

Optimizations

• There may be a lot of false sharing in lzma. State; check whether this can be improved by reorganizing the internal structure of it.

• Check whether batching encoding and decoding improves speed.

DAG optimizations

• Use full buffer to create minimal bit-length above range encoder.
• Might be too slow (see v0.4)

Different match finders

• hashes with 2, 3 characters additional to 4 characters

• binary trees with 2-7 characters (uint64 as key, use uint32 as

  pointers into a an array)

• rb-trees with 2-7 characters (uint64 as key, use uint32 as pointers

  into an array with bit-steeling for the colors)

Release Procedure

• execute goch -l for all packages; probably with lower param like 0.5.
• check orthography with gospell
• Write release notes in doc/relnotes.
• Update README.md
• xb copyright . in xz directory to ensure all new files have Copyright header
• VERSION=<version> go generate github.com/ulikunitz/xz/... to update version files
• Execute test for Linux/amd64, Linux/x86 and Windows/amd64.
• Update TODO.md - write short log entry
• git checkout master && git merge dev
• git tag -a <version>
• git push

Log

2021-02-02

Mituo Heijo has fuzzed xz and found a bug in the function readIndexBody. The function allocated a slice of records immediately after reading the value without further checks. Since the number has been too large the make function did panic. The fix is to check the number against the expected number of records before allocating the records.

2020-12-17

Release v0.5.9 fixes warnings, a typo and adds SECURITY.md.

One fix is interesting.

const (
  a byte = 0x1
  b      = 0x2
)

The constants a and b don't have the same type. Correct is

const (
  a byte = 0x1
  b byte = 0x2
)

2020-08-19

Release v0.5.8 fixes issue issue #35.

2020-02-24

Release v0.5.7 supports the check-ID None and fixes issue #27.

2019-02-20

Release v0.5.6 supports the go.mod file.

2018-10-28

Release v0.5.5 fixes issues #19 observing ErrLimit outputs.

2017-06-05

Release v0.5.4 fixes issues #15 of another problem with the padding size check for the xz block header. I removed the check completely.

2017-02-15

Release v0.5.3 fixes issue #12 regarding the decompression of an empty XZ stream. Many thanks to Tomasz Kłak, who reported the issue.

2016-12-02

Release v0.5.2 became necessary to allow the decoding of xz files with 4-byte padding in the block header. Many thanks to Greg, who reported the issue.

2016-07-23

Release v0.5.1 became necessary to fix problems with 32-bit platforms. Many thanks to Bruno Brigas, who reported the issue.

2016-07-04

Release v0.5 provides improvements to the compressor and provides support for the decompression of xz files with multiple xz streams.

2016-01-31

Another compression rate increase by checking the byte at length of the best match first, before checking the whole prefix. This makes the compressor even faster. We have now a large time budget to beat the compression ratio of the xz tool. For enwik8 we have now over 40 seconds to reduce the compressed file size for another 7 MiB.

2016-01-30

I simplified the encoder. Speed and compression rate increased dramatically. A high compression rate affects also the decompression speed. The approach with the buffer and optimizing for operation compression rate has not been successful. Going for the maximum length appears to be the best approach.

2016-01-28

The release v0.4 is ready. It provides a working xz implementation, which is rather slow, but works and is interoperable with the xz tool. It is an important milestone.

2016-01-10

I have the first working implementation of an xz reader and writer. I'm happy about reaching this milestone.

2015-12-02

I'm now ready to implement xz because, I have a working LZMA2 implementation. I decided today that v0.4 will use the slow encoder using the operations buffer to be able to go back, if I intend to do so.

2015-10-21

I have restarted the work on the library. While trying to implement LZMA2, I discovered that I need to resimplify the encoder and decoder functions. The option approach is too complicated. Using a limited byte writer and not caring for written bytes at all and not to try to handle uncompressed data simplifies the LZMA encoder and decoder much. Processing uncompressed data and handling limits is a feature of the LZMA2 format not of LZMA.

I learned an interesting method from the LZO format. If the last copy is too far away they are moving the head one 2 bytes and not 1 byte to reduce processing times.

2015-08-26

I have now reimplemented the lzma package. The code is reasonably fast, but can still be optimized. The next step is to implement LZMA2 and then xz.

2015-07-05

Created release v0.3. The version is the foundation for a full xz implementation that is the target of v0.4.

2015-06-11

The gflag package has been developed because I couldn't use flag and pflag for a fully compatible support of gzip's and lzma's options. It seems to work now quite nicely.

2015-06-05

The overflow issue was interesting to research, however Henry S. Warren Jr. Hacker's Delight book was very helpful as usual and had the issue explained perfectly. Fefe's information on his website was based on the C FAQ and quite bad, because it didn't address the issue of -MININT == MININT.

2015-06-04

It has been a productive day. I improved the interface of lzma. Reader and lzma. Writer and fixed the error handling.

2015-06-01

By computing the bit length of the LZMA operations I was able to improve the greedy algorithm implementation. By using an 8 MByte buffer the compression rate was not as good as for xz but already better then gzip default.

Compression is currently slow, but this is something we will be able to improve over time.

2015-05-26

Checked the license of ogier/pflag. The binary lzmago binary should include the license terms for the pflag library.

I added the endorsement clause as used by Google for the Go sources the LICENSE file.

2015-05-22

The package lzb contains now the basic implementation for creating or reading LZMA byte streams. It allows the support for the implementation of the DAG-shortest-path algorithm for the compression function.

2015-04-23

Completed yesterday the lzbase classes. I'm a little bit concerned that using the components may require too much code, but on the other hand there is a lot of flexibility.

2015-04-22

Implemented Reader and Writer during the Bayern game against Porto. The second half gave me enough time.

2015-04-21

While showering today morning I discovered that the design for OpEncoder and OpDecoder doesn't work, because encoding/decoding might depend on the current status of the dictionary. This is not exactly the right way to start the day.

Therefore we need to keep the Reader and Writer design. This time around we simplify it by ignoring size limits. These can be added by wrappers around the Reader and Writer interfaces. The Parameters type isn't needed anymore.

However I will implement a ReaderState and WriterState type to use static typing to ensure the right State object is combined with the right lzbase. Reader and lzbase. Writer.

As a start I have implemented ReaderState and WriterState to ensure that the state for reading is only used by readers and WriterState only used by Writers.

2015-04-20

Today I implemented the OpDecoder and tested OpEncoder and OpDecoder.

2015-04-08

Came up with a new simplified design for lzbase. I implemented already the type State that replaces OpCodec.

2015-04-06

The new lzma package is now fully usable and lzmago is using it now. The old lzma package has been completely removed.

2015-04-05

Implemented lzma. Reader and tested it.

2015-04-04

Implemented baseReader by adapting code form lzma. Reader.

2015-04-03

The opCodec has been copied yesterday to lzma2. opCodec has a high number of dependencies on other files in lzma2. Therefore I had to copy almost all files from lzma.

2015-03-31

Removed only a TODO item.

However in Francesco Campoy's presentation "Go for Javaneros (Javaïstes?)" is the the idea that using an embedded field E, all the methods of E will be defined on T. If E is an interface T satisfies E.

https://talks.golang.org/2014/go4java.slide#51

I have never used this, but it seems to be a cool idea.

2015-03-30

Finished the type writerDict and wrote a simple test.

2015-03-25

I started to implement the writerDict.

2015-03-24

After thinking long about the LZMA2 code and several false starts, I have now a plan to create a self-sufficient lzma2 package that supports the classic LZMA format as well as LZMA2. The core idea is to support a baseReader and baseWriter type that support the basic LZMA stream without any headers. Both types must support the reuse of dictionaries and the opCodec.

2015-01-10

1. Implemented simple lzmago tool
2. Tested tool against large 4.4G file
   • compression worked correctly; tested decompression with lzma
   • decompression hits a full buffer condition
3. Fixed a bug in the compressor and wrote a test for it
4. Executed full cycle for 4.4 GB file; performance can be improved ;-)

2015-01-11

• Release v0.2 because of the working LZMA encoder and decoder