Qhull and scripts/geometry

[Petr Mikulik]

> >>> >> | Yes; configuring Qhull with
> >>> >> |     CFLAGS="-fno-strict-aliasing -O2" ./configure $*
> >>> >> | does not crash the testing command
> >>> >> |      rbox c D3 | qconvex s G
> >>> >> |
> >>> >> | Could Octave's ./configure test the Qhull library? I propose that if the
> >>> >> | above test command (or some C++ source test case) crashes, then Octave does
> >>> >> | not link to Qhull library and writes a hint like
> >>> >> |   Crashing Qhull found; please recompile the Qhull library by
> >>> >> |     CFLAGS="-fno-strict-aliasing -O2" ./configure; make
> >>> >>
> >>> >> Can you provide an autoconf macro that does the test and does not
> >>> >> require an external program?  My Debian sysstem has the library but
> >>> >> the test programs are not installed.
> >>> >>
> >>> >> There is also the issue that running test programs limits the
> >>> >> usefulness of configure scripts when cross-compiling.  In this case, I
> >>> >> guess we would just have to assume that the library works when cross
> >>> >> compiling.
> >>> >
> >>> > I've prepared the shortest code that leads to crash if the Qhull library has
> >>> > been compiled without the appropriate CFLAGS.
> >>> >
> >>> > Usage:
> >>> >    gcc -o QhullCrashTest QhullCrashTest.c -lqhull -lm
> >>> >    echo "2 4 -0.5 -0.5 -0.5 0.5 0.5 -0.5 0.5 0.5" | ./QhullCrashTest
> >>> >
> >>> > If it crashes, nothing is written on stdout.
> >>> > If it does not crash, an "OK message" is written on stdout.
> >>> >
> >>> > Could this testing program be used in the Octave configure?
> >>> > I don't know how to write an autoconf macro for it.
> >>> >
> >>>
> >>> Hi Petr,
> >>>
> >>> I'll take care of the inclusion into configure. However, for best
> >>> suitability for autoconf macros (AC_RUN_IFELSE), please modify the
> >>> test program in the following manner:
> >>> 1. make the inputs part of the source
> >>> 2. indicate success by returning exit code zero. If you can do it, to
> >>> make the test more complete, I suggest also to check the results for
> >>> correctness (if a crash doesn't happen on some system, but instead
> >>> incorrect results are produced).
> >>
> >> I have no idea how to put the input data into the testing program.
> >>
> >
> > I have taken a quick look at it and it seems the attached source is
> > able to reproduce the crash. Would you please verify with your
> > configuration?

Yes, it reproduces the crash.

> >> The success is indicated by zero exit code ("return 0"); failure is
> >> indicated by crash with a "Segmentation fault" ... the return value seems to
> >> be 139.
> >
> > Yes, this is indicated by the system (and autoconf macro handles it).
> > I am, however, very suspicious about regarding a segfault as something
> > predictable; it depends on the OS and perhaps other circumstances.
> > It would be even better to check the results for correctness (see, for
> > instance, the analogous checks for correctness of BLAS library called
> > from Fortran); still, I'd be happy even with this. I'll turn this into
> > a patch.
>
> Patch attached. Comments? OK to push?

It's OK with me.

Minor thing: I propose that ./configure writes a description why it has 
refused the Qhull library, for example:

  Crashing Qhull library detected. Please recompile it
  with CFLAGS="-fno-strict-aliasing -O2" 

---
Petr Mikulik