strange clobber of values in Math::Complex

[p5pRT]

Migrated from rt.perl.org#61142 (status was 'resolved')

Searchable as RT61142$

[p5pRT]

From david.madore@ens.fr

This is a bug report for perl from david.madore@​ens.fr,
generated with the help of perlbug 1.36 running under perl 5.10.0.

---

The following program​:

### cut after this line ###
#! /usr/local/bin/perl -w

use strict;
use warnings;
use Math​::Complex;

sub stupid {
  my $q = shift;
  my $qn = $q;
  while ( $qn >= 1.e-20 ) {
  $qn *= $q;
  }
}

my $z = Math​::Complex->make(0.5,0.5*sqrt(15));
$z = -1/$z; # Comment this for correct (but different) result!
my $q = exp(2*i*pi*$z);
stupid($q); # Comment this for correct result!
my $q2 = $q + 0.; # (Force printing in cartesian; this is unimportant)
print "z=$z\nq=$q2\n";
### cut before this line ###

gives the following output (with Debian's 5.10.0-17 both under i386
and amd64)​:

z=-0.125+0.484122918275927i
q=-5.19748331237927e-06+6.36508130212706e-22i

This is obviously wrong​: q is not exp(2*i*pi*z). The strangest thing
is​: if we remove the call to stupid($q) (which ought to do nothing at
all!) then the printed value for q is correct; and, as such, the
printed value for q is actually exp(2*i*pi*z0) where z0 is the
original value of z (before the $z=-1/$z line).

Am I out of my mind, or is this utterly broken?

---

---

Flags​:
  category=library
  severity=medium

---

Site configuration information for perl 5.10.0​:

Configured by Debian Project at Sun Nov 2 07​:30​:08 UTC 2008.

Summary of my perl5 (revision 5 version 10 subversion 0) configuration​:
  Platform​:
  osname=linux, osvers=2.6.22-3-vserver-amd64, archname=x86_64-linux-gnu-thread-multi
  uname='linux excelsior 2.6.22-3-vserver-amd64 #1 smp tue feb 12 10​:01​:41 utc 2008 x86_64 gnulinux '
  config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.10 -Darchlib=/usr/lib/perl/5.10 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.10.0 -Dsitearch=/usr/local/lib/perl/5.10.0 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.10.0 -Dd_dosuid -des'
  hint=recommended, useposix=true, d_sigaction=define
  useithreads=define, usemultiplicity=define
  useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
  use64bitint=define, use64bitall=define, uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
  optimize='-O2 -g',
  cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include'
  ccversion='', gccversion='4.3.2', gccosandvers=''
  intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
  ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
  alignbytes=8, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib /lib64 /usr/lib64
  libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
  perllibs=-ldl -lm -lpthread -lc -lcrypt
  libc=/lib/libc-2.7.so, so=so, useshrplib=true, libperl=libperl.so.5.10.0
  gnulibc_version='2.7'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
  cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib'

Locally applied patches​:
 

---

@​INC for perl 5.10.0​:
  /etc/perl
  /usr/local/lib/perl/5.10.0
  /usr/local/share/perl/5.10.0
  /usr/lib/perl5
  /usr/share/perl5
  /usr/lib/perl/5.10
  /usr/share/perl/5.10
  /usr/local/lib/site_perl
  .

---

Environment for perl 5.10.0​:
  HOME=/home/david
  LANG=C
  LANGUAGE (unset)
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/home/david/bin/vega.stars​:/home/david/bin/x86_64​:/home/david/bin​:/usr/local/bin​:/bin​:/usr/bin​:/usr/X11R6/bin​:/usr/local/games​:/usr/games
  PERL_BADLANG (unset)
  SHELL=/bin/zsh

[p5pRT]

From @chorny

I have reported this bug to bug tracker of Math​::Complex, with seriously
simplified test case. See https://rt.cpan.org/Ticket/Display.html?id=56149

Problem is missing copy constructor.

On Sun Dec 07 15​:13​:24 2008, david.madore@​ens.fr wrote​:

This is a bug report for perl from david.madore@​ens.fr,
generated with the help of perlbug 1.36 running under perl 5.10.0.

-----------------------------------------------------------------

The following program​:

### cut after this line ###
#! /usr/local/bin/perl -w

use strict;
use warnings;
use Math​::Complex;

sub stupid {
my $q = shift;
my $qn = $q;
while ( $qn >= 1.e-20 ) {
$qn *= $q;
}
}

my $z = Math​::Complex->make(0.5,0.5*sqrt(15));
$z = -1/$z; # Comment this for correct (but different) result!
my $q = exp(2*i*pi*$z);
stupid($q); # Comment this for correct result!
my $q2 = $q + 0.; # (Force printing in cartesian; this is
unimportant)
print "z=$z\nq=$q2\n";
### cut before this line ###

gives the following output (with Debian's 5.10.0-17 both under i386
and amd64)​:

z=-0.125+0.484122918275927i
q=-5.19748331237927e-06+6.36508130212706e-22i

This is obviously wrong​: q is not exp(2*i*pi*z). The strangest thing
is​: if we remove the call to stupid($q) (which ought to do nothing at
all!) then the printed value for q is correct; and, as such, the
printed value for q is actually exp(2*i*pi*z0) where z0 is the
original value of z (before the $z=-1/$z line).

Am I out of my mind, or is this utterly broken?

-----------------------------------------------------------------

--
Alexandr Ciornii, http​://chorny.net

[p5pRT]

The RT System itself - Status changed from 'new' to 'open'

[p5pRT]

From @obra

Resolving per chorny

[p5pRT]

@obra - Status changed from 'open' to 'resolved'