Re: minGW 'make check' errors

[PhilipNienhuis]

Rik-4 wrote
> 11/3/13
> 
> This bug report details some errors which apparently only appear on the
> minGW system (https://savannah.gnu.org/bugs/?32036).
> 
> Specifically, it seems that log2 (Inf) = Inf on all other platforms and
> NaN
> on minGW.  Given that minGW is linking against Windows math libraries, and
> I don't see Microsoft changing anytime soon, I think we should make
> exceptions for these two tests when minGW is detected.  After all,
> reporting them as failures isn't going to change Octave's code (log2(Inf)
> should be Inf), nor is it going to be a spur to Microsoft to change their
> libraries.  Thus, the point of a failing test being a prod to get
> something
> fixed is rendered moot.

Is that true, that it is Windows' low-level math libs that screw up? I'd
expect that they are as tied to the HW (CPU/FPU) as e.g., Linux low-level
math libs. I really see no reason for Microsoft to stick to returning
inappropriate numeric exception values given the enormous proliferation of
Windows in the engineering and scientific world. But I really don't know the
exact details.

I'd rather expect that it is MinGW runtime math libs ("upstream") that get
things wrong. An example of MinGW low-level code is here:
https://www.gitorious.org/mingw/mingw-runtime/source/77108e3eb6c1896f3d1aa5ad7dcd2d8225280125:mingwex/math/powl.c
My C/C++ skills surely are somewhat lacking but this code piece suggests me
it cannot be ruled out yet that the key is in the MinGW math libs.
FYI, Python seems to have wrappers for special values, see:
http://bugs.python.org/review/11888/diff/2544/Modules/mathmodule.c?context=75&column_width=80
Wrappers give me a taste of performance hits, but maybe they can be
implemented cleverly.

Makes me wonder what Michael Goffioul's MSVC binaries make of it.

But before filing bug reports upstream we'd need to be very sure it isn't in
any way Octave's fault that we get Inf vs. NaN or vice versa on MinGW.

We probably cannot compare with Matlab - that is I've read rumours that ML
supplies its own math libraries. But I'll try to test it at work. Stupid of
me, never thought of it.

Anyway, this bug report isn't in the way. Maybe someday, somehow we'll find
a fix for it.

Philip




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