Fixes to avoid multiple definitions for thread pools and suppress compiler warnings.

[cheshyre]

When using the ips4o parallel sort via normal Makefiles, I ran into multiple definition errors when compiling associated with the various *ThreadPool Impl structs. I inlined all the associated functions where the definition was separated from the declaration, which resolved the errors. This is the first commit in the PR.

In addition, I attempted to suppress most of the (presumably spurious) compiler warnings when including the ips4o headers. (I did this for -Wall -Wextra -Wpedantic, but I typically don't use pedantic so I don't actually care about the warnings associated with __int128.) The remaining warning, as far as I get them at least, is associated with classifier.h:131:

./lib/ips4o/include/ips4o/classifier.hpp:131:28: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]

I attempted to add parentheses and such to make this warning go away, but the compiler seems to be hung up on something here. I don't fully understand the control flow of this function, but if you can explain it to me or have some ideas regarding the warning, I would be happy to take another look at the warning and try and suppress it.

Thanks for your time and feedback!

[Morwenn]

Unless I'm mistaken, you can also use __uint128_t to avoid the pedantic warning without having to use __extension__.

[cheshyre]

It seems that it does, and a quick Google suggests that it supported by at least Clang, GCC, and Intel's compiler. I don't know enough about compilers and support to say for certain that this is a safe replacement, but if it is then it might be preferable to __extension__.

[Morwenn]

I'm unfortunately no more knowledgeable, I just know that the use of __int128_t and __uint128_t is somewhat widespread and have the advantage of being "normal" from the language POV, just another type which happens to have compiler support.

[ips4o]

Thank you for your recommendation. However, I would prefer a cast to int, the type of log_buckets_.

[ips4o]

I would prefer to remove the unused function parameters.

[cheshyre]

I went through and adopted the suggestions:

• The static cast to avoid signed-unsiged comparison is now to int instead of std::int64_t.
• Unused parameters have been removed and the function calls have been adjusted. Similarly, unused values have been completely removed. (This should be tested by somebody that knows the code well because I do not know whether getting the shared pointer on line 480 of parallel.hpp had any important side effects.
  In my testing, the sort still works correctly in serial and parallel contexts, but I'm not sure if there is a more comprehensive test suite that could be run.