unexpected NV conversion in numeric comparison + overloading

[p5pRT]

Migrated from rt.perl.org#77456 (status was 'resolved')

Searchable as RT77456$

[p5pRT]

From @ntyni

This is a bug report for perl from Niko Tyni <ntyni@​debian.org>,
generated with the help of perlbug 1.39 running under perl 5.13.4.

---

As seen in [rt.cpan.org #59478] and http​://bugs.debian.org/593764
overloading numeric conversion and then doing numeric comparison triggers
an unexpected IV -> NV conversion behind the scenes.

Test 1 of the following script fails with 64-bit integers and 64-bit
doubles because precision is lost in the conversion process.

While I can see that this may not be a bug at all, consider that
it was originally seen with the Moose test suite where an object was
overloaded to numify as its refaddr() value. Having two objects compare
as equivalent is certainly surprising behaviour here, particularly as
it only showed up on the ia64 ("Itanium") architecture where refaddr()
returns big integers instead of small ones.

Anyway, feel free to close this ticket if it's all working as it should.

#!perl

package Foo;

my $i = 1 << 53;
use overload '0+' => sub { $i++ },
  fallback => 1;
1;

package main;

print "1..2\n";
my $f1 = bless {}, 'Foo';
my $f2 = bless {}, 'Foo';

print ((($f1 == $f2) ? "not " : "") . "ok 1 - equivalence first\n");
print (((0+$f1 == 0+$f2) ? "not " : "") . "ok 2 - numification first\n");
__END__

---

---

Flags​:
  category=core
  severity=low

---

Site configuration information for perl 5.13.4​:

Configured by niko at Thu Aug 26 19​:13​:41 EEST 2010.

Summary of my perl5 (revision 5 version 13 subversion 4) configuration​:
  Derived from​: 1a0a2ba
  Platform​:
  osname=linux, osvers=2.6.32-5-amd64, archname=x86_64-linux-gnu-thread-multi
  uname='linux madeleine 2.6.32-5-amd64 #1 smp thu aug 12 13​:01​:50 utc 2010 x86_64 gnulinux '
  config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.13 -Darchlib=/usr/lib/perl/5.13 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.13.4 -Dsitearch=/usr/local/lib/perl/5.13.4 -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=both -Doptimize=-O0 -Dusedevel -Uuseshrplib -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 -DDEBUGGING -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
  optimize='-O0 -g',
  cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -DDEBUGGING -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
  ccversion='', gccversion='4.4.5 20100816 (prerelease)', 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 =' -fstack-protector -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib /lib64 /usr/lib64
  libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc -lgdbm_compat
  perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
  libc=/lib/libc-2.11.2.so, so=so, useshrplib=false, libperl=libperl.a
  gnulibc_version='2.11.2'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
  cccdlflags='-fPIC', lddlflags='-shared -O0 -g -L/usr/local/lib -fstack-protector'

Locally applied patches​:
 

---

@​INC for perl 5.13.4​:
  lib
  /usr/local/lib/perl/5.13.4
  /usr/local/share/perl/5.13.4
  /usr/lib/perl5
  /usr/share/perl5
  /usr/lib/perl/5.13
  /usr/share/perl/5.13
  /usr/local/share/perl
  /usr/share/perl5
  .

---

Environment for perl 5.13.4​:
  HOME=/home/niko
  LANG=en_US.UTF-8
  LANGUAGE (unset)
  LC_CTYPE=fi_FI.UTF-8
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/home/niko/bin​:/home/niko/bin​:/home/niko/bin​:/usr/local/bin​:/usr/bin​:/bin​:/usr/local/games​:/usr/games​:/sbin​:/usr/sbin​:/sbin​:/usr/sbin
  PERL_BADLANG (unset)
  SHELL=/bin/zsh

[p5pRT]

From zefram@fysh.org

Niko Tyni wrote​:

As seen in [rt.cpan.org #59478] and http​://bugs.debian.org/593764
overloading numeric conversion and then doing numeric comparison triggers
an unexpected IV -> NV conversion behind the scenes.

This also strongly resembles [perl #46011].

-zefram

[p5pRT]

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

[p5pRT]

From @iabyn

On Thu, Aug 26, 2010 at 12​:37​:03PM -0700, Niko Tyni wrote​:

As seen in [rt.cpan.org #59478] and http​://bugs.debian.org/593764
overloading numeric conversion and then doing numeric comparison triggers
an unexpected IV -> NV conversion behind the scenes.

Test 1 of the following script fails with 64-bit integers and 64-bit
doubles because precision is lost in the conversion process.

While I can see that this may not be a bug at all, consider that
it was originally seen with the Moose test suite where an object was
overloaded to numify as its refaddr() value. Having two objects compare
as equivalent is certainly surprising behaviour here, particularly as
it only showed up on the ia64 ("Itanium") architecture where refaddr()
returns big integers instead of small ones.

Anyway, feel free to close this ticket if it's all working as it should.

#!perl

package Foo;

my $i = 1 << 53;
use overload '0+' => sub { $i++ },
fallback => 1;
1;

package main;

print "1..2\n";
my $f1 = bless {}, 'Foo';
my $f2 = bless {}, 'Foo';

print ((($f1 == $f2) ? "not " : "") . "ok 1 - equivalence first\n");
print (((0+$f1 == 0+$f2) ? "not " : "") . "ok 2 - numification first\n");

Now fixed with this commit​:

commit a42d024
Author​: David Mitchell <davem@​iabyn.com>
AuthorDate​: Wed Dec 15 19​:38​:17 2010 +0000
Commit​: David Mitchell <davem@​iabyn.com>
CommitDate​: Wed Dec 15 19​:41​:46 2010 +0000

  don't upgrade overload IV return values to NV
 
  (if we can avoid it).
 
  Fix for RT #77456. Basically it extends the usage of the AMGf_numeric flag
  to the remaining overloadable numeric ops that behave differently with IV
  and NV.

Affected files ...
 
  M lib/overload64.t
  M pp.c
  M pp_hot.c

--
Modern art​:
  "That's easy, I could have done that!"
  "Ah, but you didn't!"

[p5pRT]

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