zlib data compression library for the next generation systems

Maintained by Hans Kristian Rosbach aka Dead2 (zlib-ng àt circlestorm dót org)

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• Zlib compatible API with support for dual-linking
• Modernized native API based on zlib API for ease of porting
• Modern C99 syntax and a clean code layout
• Deflate medium and quick algorithms based on Intels zlib fork
• Support for CPU intrinsics when available
  • Adler32 implementation using SSSE3, AVX2, Neon & VSX
  • CRC32-B implementation using PCLMULQDQ & ACLE
  • Hash table implementation using CRC32-C intrinsics on x86 and ARM
  • Slide hash implementations using SSE2, AVX2, Neon & VSX
  • Compare256/258 implementations using SSE4.2 & AVX2
  • Inflate chunk copying using SSE2, AVX2 & Neon
  • Support for hardware-accelerated deflate using IBM Z DFLTCC
• Unaligned memory read/writes and large bit buffer improvements
• Includes improvements from Cloudflare and Intel forks
• Configure, CMake, and NMake build system support
• Comprehensive set of CMake unit tests
• Code sanitizers, fuzzing, and coverage
• GitHub Actions continuous integration on Windows, macOS, and Linux
  • Emulated CI for ARM, AARCH64, PPC, PPC64, SPARC64, S390x using qemu

The motivation for this fork was due to seeing several 3rd party contributions containing new optimizations not getting implemented into the official zlib repository.

Mark Adler has been maintaining zlib for a very long time, and he has done a great job and hopefully he will continue for a long time yet. The idea of zlib-ng is not to replace zlib, but to co-exist as a drop-in replacement with a lower threshold for code change.

zlib has a long history and is incredibly portable, even supporting lots of systems that predate the Internet. This is great, but it does complicate further development and maintainability. The zlib code has numerous workarounds for old compilers that do not understand ANSI-C or to accommodate systems with limitations such as operating in a 16-bit environment.

Many of these workarounds are only maintenance burdens, some of them are pretty huge code-wise. For example, the [v]s[n]printf workaround code has a whopping 8 different implementations just to cater to various old compilers. With this many workarounds cluttered throughout the code, new programmers with an idea/interest for zlib will need to take some time to figure out why all of these seemingly strange things are used, and how to work within those confines.

So I decided to make a fork, merge all the Intel optimizations, merge the Cloudflare optimizations that did not conflict, plus a couple of other smaller patches. Then I started cleaning out workarounds, various dead code, all contrib and example code as there is little point in having those in this fork for various reasons.

A lot of improvements have gone into zlib-ng since its start, and numerous people and companies have contributed both small and big improvements, or valuable testing.

Please read LICENSE.md, it is very simple and very liberal.

There are two ways to build zlib-ng:

To build zlib-ng using the cross-platform makefile generator cmake.

cmake .
cmake --build . --config Release
ctest --verbose -C Release

Alternatively, you can use the cmake configuration GUI tool ccmake:

ccmake .

To build zlib-ng using the bash configure script:

./configure
make
make test

WARNING: We do not recommend manually installing unless you really know what you are doing, because this can potentially override the system default zlib library, and any incompatibility or wrong configuration of zlib-ng can make the whole system unusable, requiring recovery or reinstall. If you still want a manual install, we recommend using the /opt/ path prefix.

For Linux distros, an alternative way to use zlib-ng (if compiled in zlib-compat mode) instead of zlib, is through the use of the LD_PRELOAD environment variable. If the program is dynamically linked with zlib, then zlib-ng will temporarily be used instead by the program, without risking system-wide instability.

LD_PRELOAD=/opt/zlib-ng/libz.so.1.2.11.zlib-ng /usr/bin/program

To install zlib-ng system-wide using cmake:

cmake --build . --target install

To install zlib-ng system-wide using the configure script:

make install

Zlib-ng is a aiming to be open to contributions, and we would be delighted to receive pull requests on github. Just remember that any code you submit must be your own and it must be zlib licensed. Help with testing and reviewing of pull requests etc is also very much appreciated.

If you are interested in contributing, please consider joining our IRC channel #zlib-ng on the Freenode IRC network.

Thanks to Servebolt.com for sponsoring my maintainership of zlib-ng.

Thanks go out to all the people and companies who have taken the time to contribute code reviews, testing and/or patches. Zlib-ng would not have been nearly as good without you.

The deflate format used by zlib was defined by Phil Katz. The deflate and zlib specifications were written by L. Peter Deutsch.

zlib was originally created by Jean-loup Gailly (compression) and Mark Adler (decompression).