json_writer: improve isfinite support on *nix

[mathstuf]

Based on a patches to CMake by:

Ådne Hovda [email protected]:

commit 7b1cdb00279908cacabada92f8a53e4986465423

jsoncpp: Provide 'isfinite' implementation on older AIX and HP-UX

Newer AIX and HP-UX platforms provide 'isfinite' as a <math.h> macro.
Older versions do not, so add the definition if it is not provided.

Michael Scott [email protected]:

commit 9217b678b305d7df7471ba476a81bf28961fdfa3

jsoncpp: Provide 'isfinite' impl on more HP-UX versions (#15576)

Some versions of HP-UX do not define 'isfinite' or 'finite' in math.h
for Itanium when preprocessing with C++, so we have to add the
definition ourselves instead to map to the internal version.

Joerg Sonnenberger [email protected]:

commit 75644dafe54c21902f14cfe58cb8338b553b69d8

jsoncpp: Fix compilation as C99 on Solaris

In C99 mode, Solaris variants may already define isfinite, so check for
the existence first.

[mathstuf]

@bradking

[mathstuf]

Links to the cmake commits: Kitware/CMake@7b1cdb0 Kitware/CMake@9217b67 Kitware/CMake@75644da.

If you'd like these split as they came into CMake, let me know and I'll redo the branch.

[cdunn2001]

Wow. So much work for a value that is not even part of standard JSON.

Anyway, thanks! Looks good to me. One question: Can <math.h> be <cmath> on those platforms? Some compilers will warn about non-standard includes. It's not a huge problem. Just asking.

[mathstuf]

Yeah, math.h is a fun bit of the standard-meets-reality story. As for headers, I don't know :( . Brad?

[bradking]

CMake's last import of jsoncpp pre-dates the change from math.h to cmath, and cmath is not included anywhere in the entire CMake source tree, so I don't know whether cmath would work on those platforms. As mentioned in the commit message proposed here, the changes to CMake were all contributed by others. I don't have access to all their platforms to try it out myself. Fortunately it is only on AIX and HP-UX that math.h is included by this patch. After we next update CMake's jsoncpp version we may be able to test out cmath for this use case.