[Pkg-octave-devel] Bug#871214: Bug#871214: octave-image FTBFS on i386: test hangs

[Adrian Bunk]

On Tue, Aug 15, 2017 at 08:08:58PM +0200, Sébastien Villemot wrote:
> On Thu, Aug 10, 2017 at 02:42:42PM +0300, Adrian Bunk wrote:
> > On Thu, Aug 10, 2017 at 09:31:32AM +0200, Rafael Laboissière wrote:
> > > 
> > > I would guess that the culprit is the following unit test in bwdist:
> > > 
> > > ## The quasi-euclidean method is apparently sensitive to a machine precision
> > > ## error that happens in x86 systems only. This test will cause an endless
> > > ## loop in case of a regression.
> > >...
> > 
> > That explains why the problem happens on i386 (where the 387 FPU
> > that internally uses 80-bit precision is used) but not on amd64
> > (where gcc defaults to using SSE instead of the 387).
> > 
> > If the problem is only in the test case,
> > it should be disabled on any-i386.
> > 
> > But if the difference is actually considered a bug,
> > then the following in debian/rules fixes the problem:
> > 
> > DEB_HOST_ARCH ?= $(shell dpkg-architecture -qDEB_HOST_ARCH)
> > 
> > ifneq (,$(filter $(DEB_HOST_ARCH), i386))
> >     export DEB_CXXFLAGS_MAINT_APPEND=-ffloat-store
> > endif
> 
> Thanks Adrian for suggesting this solution.
> 
> However, it should be mentioned that this option has a significant performance
> cost (since it basically adds a memory access after each floating point
> computation).
> 
> I am not familiar enough with octave-image to decide whether IEEE compliance is
> more important than performance, though.

This is also what I tried to say by giving two options and
"But if the difference is actually considered a bug".

cu
Adrian

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