This formats all copyright comments according to SPDX formatting guidelines.
Additionally, this resolves the remaining GPLv2 only licensed files by relicensing them to GPLv2.0-or-later.
- Previous optimized impl. resulted in an integer overflow, so revert.
- This is our slow/fallback path that should never be really be used, so the optimization in unimportant.
Now that clang-format makes [[nodiscard]] attributes format sensibly, we
can apply them to several functions within the common library to allow
the compiler to complain about any misuses of the functions.
liushuyu