32-bit development

32-bit development

[Bill Maier]

I started to look into bug #46593 "Multifit test failure in 32 bit mode". My
system is Linux Mint 64-bit, and it had problems building using the 32-bit
flags described in that bug write-up. I discovered I could fix this problem
by installing g++ multilib with the command

    sudo apt-get install g++-multilib

after which the build went smoothly and I was able to duplicate the
stated problem. Not sure if the set-up for this is documented anywhere.
Besides 32-bit and 64-bit builds, are there any other build options that need to be
addressed during development?

During this process I also discovered that the hypergeometric code I
wrote for bug #45926 had a similar test failure in 32-bit mode. I'll need to
investigate and fix before that code is ready for production.

-Bill

Re: 32-bit development

[Patrick Alken]

Hi Bill,

   Yes I also reproduced the problem on an ubuntu system (compiling with 
the -m32 flag to gcc). I know in older versions of GSL (1.15 and earlier 
I think) the nonlinear least squares test suite was extremely primitive, 
so its likely the issue has existed for a long time, it just wasn't 
being tested thoroughly. In version 1.16, I added a lot of test problems 
(originally there were 4 test problems, now there are around 40.

   I don't know why the algorithm doesn't work well on 32 bit - the main 
algorithm was ported from MINPACK which is considered a highly robust 
implementation of Levenberg-Marquardt, so its puzzling why it would fail 
on 32 bit systems. Perhaps some insight could be gained by stepping 
through the iteration in a debugger using both a 32 and 64 bit build, to 
see why the results are diverging so dramatically.

   I'm sorry I haven't yet had a chance to look at your earlier patches. 
They are still on my todo list but currently I am extremely busy with 
other things. I will get to them as soon as I can!

Thanks,
Patrick

On 12/08/2015 01:44 PM, Bill Maier wrote:
> I started to look into bug #46593 "Multifit test failure in 32 bit mode". My
> system is Linux Mint 64-bit, and it had problems building using the 32-bit
> flags described in that bug write-up. I discovered I could fix this problem
> by installing g++ multilib with the command
>
>      sudo apt-get install g++-multilib
>
> after which the build went smoothly and I was able to duplicate the
> stated problem. Not sure if the set-up for this is documented anywhere.
> Besides 32-bit and 64-bit builds, are there any other build options that need to be
> addressed during development?
>
> During this process I also discovered that the hypergeometric code I
> wrote for bug #45926 had a similar test failure in 32-bit mode. I'll need to
> investigate and fix before that code is ready for production.
>
> -Bill