linalg self test failure on 32-bit machine

[Jeffrey Walton]

Hi Everyone/Patrick,

I'm building GSL master on Ubuntu 18.04.5 LTS i686 (fully patched).
The rub is, it is real 32-bit iron. It's an old Pentium III machine.

This looks like a new failure that's only present on 32-bit machines:

$ cat gsl-2.6/linalg/test-suite.log
====================================
   gsl 2.6: linalg/test-suite.log
====================================

# TOTAL: 1
# PASS:  0
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0

.. contents:: :depth: 2

FAIL: test
==========

FAIL: LU_decomp rect3: ( 80,100)[64,65]: 4.12655062968342833e-05
4.12655062973499298e-05
 (4.12655062968342833e-05 observed vs 4.12655062973499298e-05
expected) [5515924]
FAIL: cholesky_decomp unscaled random: (147,147)[92,130]:
1.06636434789185456e-07   1.0663643479347229e-07
 (1.06636434789185456e-07 observed vs 1.0663643479347229e-07 expected)
[12196119]
FAIL: cholesky_decomp unscaled random: (147,147)[130,92]:
1.06636434789185456e-07   1.0663643479347229e-07
 (1.06636434789185456e-07 observed vs 1.0663643479347229e-07 expected)
[12201667]
FAIL: cholesky_decomp scaled random: (147,147)[92,130]:
1.06636434797499932e-07   1.0663643479347229e-07
 (1.06636434797499932e-07 observed vs 1.0663643479347229e-07 expected)
[12217728]
FAIL: cholesky_decomp scaled random: (147,147)[130,92]:
1.06636434797499932e-07   1.0663643479347229e-07
 (1.06636434797499932e-07 observed vs 1.0663643479347229e-07 expected)
[12223276]

I can send over full logs, if needed/wanted. But I am guessing you can
probably duplicate it locally on a 32-bit machine or vm.

When I encounter 32-bit machine failures, I find it helpful to run
UBsan. UBsan can sometimes pinpoint where size assumptions are made,
like a long being 64-bits (an initialization will fail) or overflows
on calculations.

Jeff