According to MSVC manual (*1), cl.exe can skip including a header file
when that:
- contains #pragma once, or
- starts with #ifndef, or
- starts with #if ! defined.
GCC has a similar trick (*2), but it acts more stricter (e. g. there
must be _no tokens_ outside of #ifndef...#endif).
Sun C lacked #pragma once for a looong time. Oracle Developer Studio
12.5 finally implemented it, but we cannot assume such recent version.
This changeset modifies header files so that each of them include
strictly one #ifndef...#endif. I believe this is the most portable way
to trigger compiler optimizations. [Bug #16770]
*1: https://docs.microsoft.com/en-us/cpp/preprocessor/once
*2: https://gcc.gnu.org/onlinedocs/cppinternals/Guard-Macros.html
These headers need no rewrite. Just add some minor tweaks, like
addition of #include lines. Mainly cosmetic.
TIMET_MAX_PLUS_ONE was deleted because the macro was used from only
one place (directly write expression there).
Now that we no longer support old compilers, we can safely delete
several obsolete #ifdef gurads. Also because (as of writing) it is
impossible to compile the program using C++ compilers, lets just
entirely prohibit __cplusplus to reduce # of LOCs.
Note however that we still cannot eliminate __STDC_VERSION__ checks,
because MSVC does not define it, saying its C99 support is partial.
See also https://social.msdn.microsoft.com/Forums/vstudio/en-US/53a4fd75-9f97-48b2-aa63-2e2e5a15efa3
One day, I could not resist the way it was written. I finally started
to make the code clean. This changeset is the beginning of a series of
housekeeping commits. It is a simple refactoring; split internal.h into
files, so that we can divide and concur in the upcoming commits. No
lines of codes are either added or removed, except the obvious file
headers/footers. The generated binary is identical to the one before.
卜部昌平