[Buildroot] [PATCH 2/2] package/fftw: Enable multiple precision installation

[Matt Flax]

On 21/08/16 00:18, Thomas Petazzoni wrote:
> Hello,
>
> On Sat, 20 Aug 2016 13:36:41 +1000, Matt Flax wrote:
>
>>> I don't see where you are passing this option, so from the look of it,
>>> your four packages would install over each other. Or is
>>> --enable-type-prefix the default ?
>> There are now 4 mk files. Each builds in a separate directory (fftw,
>> fftwf, fftwl, fftwq) and installs as per the recommendations from fftw.
>> All fftw packages  inherit the version, source, site, license, env,
>> conf_opts, cflags from fftw.mk. By inheriting from one single set of
>> macros, we can bump versions very easily.
>> The different precisions are added like so :
>> fftwf.mk : FFTWF_CONF_OPTS += --enable-single
>> fftwl.mk : FFTL_CONF_OPTS += --enable-long-double
>> fftwq.mk : FFTQ_CONF_OPTS += --enable-quad-precision
> I'm not talking about the Buildroot code, but what each fftw package
> will be installing. My understanding is that if you don't pass
> --enable-type-prefix, each fftw package will install exactly the same
> files, overwriting the ones written by the other fftw packages, making
> the all adventure useless.
>
>> Regarding dev files, the header files are all the same - in fact from
>> the fftw site, http://www.fftw.org/fftw2_doc/fftw_6.html#SEC69 it is
>> recommended that they all install ontop of each other :
>> ./configure; make; make install; make clean
>> ./configure --ebale-single; make; make install; make clean
>> and so on ...
> Read again this very same section, they tell you to do:
>
> ./configure --enable-type-prefix [ other options ]
> make
> make install
> make clean
> ./configure --enable-float --enable-type-prefix [ other options ]
> make
> make install
>
> See that they are using the --enable-type-prefix option I'm referring
> to?
>

Type prefix was removed in version 3 of fftw. Here for example is an 
attempt to configure with type-prefix enabled :
configure: WARNING: unrecognized options: --enable-type-prefix

type-prefix is not a problem, as it isn't used any more ... I Think the 
fftw website is a little out of date ... the point however I was trying 
to show is that they recommend installing everything on the same system 
by building and rebuilding ...

In my opinion, the bottom line is that the package fftw in buildroot is 
inadequate. For example when alsa bat selects fftw, it is implicitly 
selecting the double version of fftw because it is the first choice, 
this isn't very robust. But this is not a huge problem ... however there 
are bigger issues...

There are situations when some packages want double precision, some 
packages want single precision ... and so on ... for example, gnuradio 
has had to force no installation of SINGLE precision :
package/gnuradio/Config.in:    depends on !BR2_PACKAGE_FFTW_PRECISION_SINGLE
I asssume this is because they have to choose between double or single 
precision, merely because the current status of the buildroot package 
fftw is inadequately cobbled together.

You see, the problem arises if someone needs to link against libfftwf 
... the single version and also is using other programs which require 
the double precision version.

Fftw the package is designed to be installed on the same system with all 
precisions that are required.

My proposal is to fix this inherent problem. I will submit a new patch 
which includes all of the feedback I have been given ... such as using a 
common mk file and symbolic linking against the one hash file.
I will address the packages in the buildroot repo which depend/select fftw.

Do you think this is a good approach or is there a better way to go 
about this ?

> Another concern is that one --enable-type-prefix is used, then all
> packages that use fftw will have to use the right library name and
> header name depending on the precision they want to use. Are they all
> ready for that?
>
> Could you check the different Buildroot packages in the tree that use
> FFTW, and see how they behave, and whether they need to be changed to
> accommodate your patch?
>
> There's at least alsa-lib, gnuradio, httping, imagemagick, libvips,
> liquid-dsp and pulseaudio to look at.
>> Actually "type-prefixes" aren't used and no changes are made to the
>> names.  Double precision remains libfftw3.so.3, single precision remains
>> libfftw3f.so.3 .... and so on. There is one header file used by all and
>> it is constant.
> See above.
>
>> Literally, this patch simply allows side by side installation, as it is
>> intended to be.
> I don't see how side by side installation is possible if all four
> variants of the library install to the same libfftw3.so.3 file. Could
> you expand a bit on this?
>
> Thanks!
>
> Thomas