https://www.zlib.net/

Acknowledgments:

  The deflate format used by zlib was defined by Phil Katz.  The deflate and
  zlib specifications were written by L.  Peter Deutsch.  Thanks to all the
  people who reported problems and suggested various improvements in zlib; they
  are too numerous to cite here.

Copyright notice:

 (C) 1995-2022 Jean-loup Gailly and Mark Adler

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.

  Jean-loup Gailly        Mark Adler
  jloup@gzip.org          madler@alumni.caltech.edu

If you use the zlib library in a product, we would appreciate *not* receiving
lengthy legal documents to sign.  The sources are provided for free but without
warranty of any kind.  The library has been entirely written by Jean-loup
Gailly and Mark Adler; it does not include third-party code.

If you redistribute modified sources, we would appreciate that you include in
the file ChangeLog history information documenting your changes.  Please read
the FAQ for more information on the distribution of modified source versions.


FAQ entry #24 from https://zlib.net/zlib_faq.html, 2018-09-26:

The license says that altered source versions must be "plainly marked". So what
exactly do I need to do to meet that requirement?

You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h. In
particular, the final version number needs to be changed to f, and an
identification string should be appended to ZLIB_VERSION. Version numbers
x.x.x.f are reserved for modifications to zlib by others than the zlib
maintainers. For example, if the version of the base zlib you are altering is
1.2.3.4, then in zlib.h you should change ZLIB_VERNUM to 0x123f, and
ZLIB_VERSION to something like 1.2.3.f-zachary-mods-v3. You can also update the
version strings in deflate.c and inftrees.c.

For altered source distributions, you should also note the origin and nature of
the changes in zlib.h, as well as in ChangeLog and README, along with the dates
of the alterations. The origin should include at least your name (or your
company's name), and an email address to contact for help or issues with the
library.

Note that distributing a compiled zlib library along with zlib.h and zconf.h is
also a source distribution, and so you should change ZLIB_VERSION and
ZLIB_VERNUM and note the origin and nature of the changes in zlib.h as you
would for a full source distribution.

