[Wien] IEEE_UNDERFLOW_FLAG IEEE_DENORMAL

Tue May 29 12:36:53 CEST 2018

On Wed, 2018-05-09 at 14:17 -0500, Laurence Marks wrote:
> You are right, this is a bug (potentially severe). In my local
> version I replaced somm with a more standard integration as somm
> interpolates to the origin (which is not right).

Will there be a fix for this bug?

Best regards
Pavel
> 
> On Wed, May 9, 2018 at 2:11 PM, Pavel Ondračka <pavel.ondracka at email.
> cz> wrote:
> > ---------- Původní e-mail ----------
> > Od: Laurence Marks <L-marks at northwestern.edu>
> > Komu: A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac
> > .at>
> > Datum: 9. 5. 2018 18:18:21
> > Předmět: Re: [Wien] IEEE_UNDERFLOW_FLAG IEEE_DENORMAL
> > 
> > > Zamt is set by somm, which is a slightly inaccurate Simpson
> > > summation (the accuracy does not matter). Hence it does not need
> > > to be set previously.
> > 
> > Right, it is indeed set in the somm subroutine. The problem is that
> > the DA variable (the local name for zamt variable in the somm
> > subroutine) is set for the first time on line 11, while it is used
> > (read) for the first time earlier on line 10 (and this is the line
> > when the gcc and valgrind complains)! Hence when the subroutine is
> > called for the first time, the results depends on read from
> > uninitialized memory.
> > Best regards
> > Pavel
> >  
> > > _____
> > > Professor Laurence Marks
> > > "Research is to see what everybody else has seen, and to think
> > > what nobody else has thought", Albert Szent-Gyorgi
> > > www.numis.northwestern.edu
> > > 
> > > On Wed, May 9, 2018, 10:42 AM Pavel Ondračka <pavel.ondracka at emai
> > > l.cz> wrote:
> > > > Laurence Marks píše v St 09. 05. 2018 v 11:51 +0000:
> > > > > This appears to be due to a silly approach in gfortran, and
> > > > almost
> > > > > certainly is not an error/problem and can be ignored -- see h
> > > > ttps://urldefense.proofpoint.com/v2/url?u=https-
> > > > 3A__s&d=DwIGaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=
> > > > U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=R1lxmwh4Y3r4yRx1Z
> > > > yR4NN9mpSe7RuaT974qRm6Uhfw&s=KDobN5dacXxTk7OUpO1BdJBY45FBX34Hf6
> > > > Q9hTempg0&e=
> > > > > tackoverflow.com/questions/44308577/ieee-underflow-flag-ieee-
> > > > > denormal-in-fortran-77.
> > > > > 
> > > > 
> > > > While I do agree that in most cases this is harmless, it can
> > > > also
> > > > suggest a bug.
> > > > 
> > > > I only looked at dstart for the TiC and I have this specific
> > > > example:
> > > > 
> > > > dstart for a TiC case prints a "Note: The following floating-
> > > > point
> > > > exceptions are signalling: IEEE_DENORMAL" line. If you trap
> > > > this with
> > > > -ffpe-trap='denormal' flag, to inspect in gdb, the offending
> > > > line is
> > > > then:
> > > > Program received signal SIGFPE, Arithmetic exception.
> > > > 0x000000000041dc48 in somm (dr=..., dp=...,
> > > > dpas=0.013585429144994965,
> > > > da=1.1588924125005173e-310, m=0, np=935) at somm.f:10
> > > > 10            D1=DA+MM
> > > > 
> > > > so this line looks completely harmless and some prints show why
> > > > the
> > > > compiler notes about this:
> > > > 
> > > > (gdb) print DA
> > > > $1 = 1.1588924125005173e-310
> > > > (gdb) print MM
> > > > $2 = 1
> > > > 
> > > > i.e. we just add a really small number (denormal, since
> > > > DOUBLE_MIN is
> > > > around 1.8e-308) to 1, which is completely OK. But lets take a
> > > > look
> > > > where this incredibly small value comes from...
> > > > 
> > > > (gdb) up
> > > > #1  0x00000000004143c6 in make_spheres (lcore=.FALSE., luse=7)
> > > > at
> > > > make_spheres.F:81
> > > > 81               call
> > > > somm(rat(1,ia),rhoat(1,ia),dx(ia),zamt,0,nptat(ia))
> > > > 
> > > > So this is the zamt variable, surprisingly grepping around for
> > > > zamt
> > > > finds nothing. As far as I can see it is not declared or
> > > > initialized
> > > > anywere in dstart. If I just missed something please correct
> > > > me! The
> > > > same goes for the zamt1 and zamt2.
> > > > 
> > > > Note that in this case we get lucky since the random memory
> > > > value is
> > > > effectively zero, however this might in my opinion lead to
> > > > problems if
> > > > you hit random memory with another value.
> > > > In fact running the dstart in vagrind shows this as well and
> > > > the
> > > > terminal is spammed with "Conditional jump or move depends on
> > > > uninitialised value(s)" and "Use of uninitialised value of size
> > > > 8".
> > > > 
> > > > IMO this is a bug, so either the line needs to be changed to 
> > > > somm(rat(1,ia),rhoat(1,ia),dx(ia),0,0,nptat(ia))
> > > > or the zamt variable needs to be declared and initialized
> > > > somewhere.
> > > > But I actually have no idea about the physical meaning of the
> > > > code so
> > > > please correct me if I just missed something.
> > > > 
> > > > Best regards
> > > > Pavel
> > > > _______________________________________________
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