At a certain step in the configuration process, `gcc -Wundef`
complained about using `INT_MAX` without a definition in png.h,
which is easily fixable with an include.
We would rather not add any extra dependencies to png.h, however,
so we use some unsigned int arithmetic magic instead.
The new libpng license comprises the terms and conditions from the zlib
license, and the disclaimer from the Boost license.
The legacy libpng license, used until libpng-1.6.35, is appended to the
new license, following the precedent established in the Python Software
Foundation License version 2.
From now on, the list of contributing authors shall be maintained in a
separate AUTHORS file.
The lists of previous contributing authors, mentioned in the legacy
libpng license and considered to be an integral part of that license,
are kept intact, with no further updates.
As per the const correctness rules, top-level const-ness of data
in automatic scopes does not propagate outside of these scopes
(unlike const-ness at lower levels, such as pointers to const data).
Previously, const was used liberally, but inconsistently across the
libpng codebase. Using const wherever applicable is not incorrect.
However, _consistent_ use of const is difficult to maintain in such
conditions.
In conclusion, we shall continue to use const only where doing so is
strictly necessary:
1. If a function guarantees that it will not modify an argument
passed by pointer, the corresponding function parameter should be
a pointer-to-const (const T *).
2. Static data should not be modified, therefore it should be const.
Reference:
Google C++ Style Guide
https://google.github.io/styleguide/cppguide.html#Use_of_const
In v1.6.0, size_t became a required type. It should be used
consistently. To maintain backwards compatibility, png_size_t
is still maintained in deprecated form.
