From stevenl@concentric.net

$ cat float.pl
#!/usr/local/bin/perl

my $t = 101.1 - 100.2;
print "value=$t\n";

$ float.pl
value=0.899999999999991

$ perl -V
Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration​:
  Platform​:
  osname=linux, osvers=2.2.1-ac1, archname=i386-linux
  uname='linux porky.devel.redhat.com 2.2.1-ac1 #1 smp mon feb 1 17​:44​:44 est 1999 i686 unknown '
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef useperlio=undef d_sfio=undef
  Compiler​:
  cc='cc', optimize='-O2', gccversion=egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)
  cppflags='-Dbool=char -DHAS_BOOL -I/usr/local/include'
  ccflags ='-Dbool=char -DHAS_BOOL -I/usr/local/include'
  stdchar='char', d_stdstdio=undef, usevfork=false
  intsize=4, longsize=4, ptrsize=4, doublesize=8
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
  alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib
  libs=-lnsl -lndbm -lgdbm -ldb -ldl -lm -lc -lposix -lcrypt
  libc=, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
  cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Characteristics of this binary (from libperl)​:
  Built under linux
  Compiled at Apr 6 1999 23​:34​:07
  @​INC​:
  /usr/lib/perl5/5.00503/i386-linux
  /usr/lib/perl5/5.00503
  /usr/lib/perl5/site_perl/5.005/i386-linux
  /usr/lib/perl5/site_perl/5.005
  .

-Steven

From [Unknown Contact. See original ticket]

I found a very basic arithmetic error in Perl (tested on Linux, Sun, and
Windows 95). What am I missing here?

$ cat float.pl
#!/usr/local/bin/perl

my $t = 101.1 - 100.2;
print "value=$t\n";

$ float.pl
value=0.899999999999991

$ perl -V
Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration​:
  Platform​:
  osname=linux, osvers=2.2.1-ac1, archname=i386-linux
  uname='linux porky.devel.redhat.com 2.2.1-ac1 #1 smp mon feb 1 17​:44​:44 est 1999 i686 unknown '
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef useperlio=undef d_sfio=undef
  Compiler​:
  cc='cc', optimize='-O2', gccversion=egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)
  cppflags='-Dbool=char -DHAS_BOOL -I/usr/local/include'
  ccflags ='-Dbool=char -DHAS_BOOL -I/usr/local/include'
  stdchar='char', d_stdstdio=undef, usevfork=false
  intsize=4, longsize=4, ptrsize=4, doublesize=8
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
  alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib
  libs=-lnsl -lndbm -lgdbm -ldb -ldl -lm -lc -lposix -lcrypt
  libc=, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
  cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Characteristics of this binary (from libperl)​:
  Built under linux
  Compiled at Apr 6 1999 23​:34​:07
  @​INC​:
  /usr/lib/perl5/5.00503/i386-linux
  /usr/lib/perl5/5.00503
  /usr/lib/perl5/site_perl/5.005/i386-linux
  /usr/lib/perl5/site_perl/5.005
  .

-Steven

From @samtregar

On 5 Oct 1999 richard@​tmtowtdi.perl.org wrote​:

I found a very basic arithmetic error in Perl (tested on Linux, Sun, and
Windows 95). What am I missing here?

You're missing the inherent uncertainty-factor of floating point
arithmatic on computers. Any basic CS text with a section on floating
point processing should be able to explain the problems to you in hideous
detail.

Summary​: it's pretty difficult to do floating point right, and it's a lot
faster just to do it wrong. In fact, it's not even totally clear what
"right" would be in some situations!

-sam

From [Unknown Contact. See original ticket]

Aaaarrgh!!

Sam Tregar <sam@​tregar.com> wrote

On 5 Oct 1999 richard@​tmtowtdi.perl.org wrote​:

Oh no he didn't. The bug report came from someone else, but we don't
know who. So your message won't have reached the originator.

And it would probably have been a good idea to point him at the
relevant FAQ entries.

Richard​:

Is there some way of finding the originator of these reports, e.g.
from the bug database? Without this info, they can't usefully be
replied to.

And if it's a choice between flattened From​: fields and getting duplicated
messages, I'd vote for duplication. But of course I'd prefer neither.

Mike Guy

From [Unknown Contact. See original ticket]

Aaaarrgh!!
Oops.

Sam Tregar <sam@​tregar.com> wrote

On 5 Oct 1999 richard@​tmtowtdi.perl.org wrote​:
Yuk.

Oh no he didn't. The bug report came from someone else, but we don't
know who. So your message won't have reached the originator.
You're right, there is also the problem of the non-reachable domain
names that appear to be reachable enough to send mail, but not to
recieve it from qmail...

And it would probably have been a good idea to point him at the
relevant FAQ entries.
It's a thought.

Is there some way of finding the originator of these reports, e.g.
from the bug database? Without this info, they can't usefully be
replied to.
Yup, I think they all went in the database OK, it's just the replies
getting stuffed.

And if it's a choice between flattened From​: fields and getting duplicated
messages, I'd vote for duplication. But of course I'd prefer neither.
Me too, believe me.

Sigh...
--
Richard Foley
+49 (0) 8121 988920 -> richard@​rfi.net

From [Unknown Contact. See original ticket]

Steven Lee <stevenl@​concentric.net> wrote

I found a very basic arithmetic error in Perl (tested on Linux, Sun, and
Windows 95). What am I missing here?

You need to understand the basic facts about floating point arithmetic.
You would get the same results with C.

See the section "Floating-point Arithmetic" in the perlop manpage,
and the first entry in perlfaq4 for more explanation​:

  Why am I getting long decimals (eg, 19.9499999999999)
  instead of the numbers I should be getting (eg, 19.95)?

Mike Guy

From [Unknown Contact. See original ticket]

Date​: Tue, 28 Aug 1956 08​:37​:41 +0000
  To​: mjtg@​cus.cam.ac.uk (M.J.T. Guy)
  Cc​: perl5-porters@​perl.org
  Subject​: Re​: [ID 19991005.003] Floating point error
  From​: richard@​rfi.net (Richard Foley)
  Message-ID​: <195608280837412609968@​slip139-92-4-218.mu.de.ibm.net>

Amazing. This must be a really early version of perl. No wonder it took
so long to get here.

<chaim>
--
Chaim Frenkel Nonlinear Knowledge, Inc.
chaimf@​pobox.com +1-718-236-0183

From [Unknown Contact. See original ticket]

Date​: Tue, 28 Aug 1956 08​:37​:41 +0000
To​: mjtg@​cus.cam.ac.uk (M.J.T. Guy)
Cc​: perl5-porters@​perl.org
Subject​: Re​: [ID 19991005.003] Floating point error
From​: richard@​rfi.net (Richard Foley)
Message-ID​:
<195608280837412609968@​slip139-92-4-218.mu.de.ibm.net>

Amazing. This must be a really early version of perl. No wonder it took
so long to get here.

<chaim>

Yeah, well, I guess I have to go change the battery in my computer...

:-)

Ciao
Richard Foley

richard@​rfi.net
"Ciao" - (shorter than 'Aufwiedersehen' :-)

From @jhi

Chaim Frenkel writes​:

Date​: Tue, 28 Aug 1956 08​:37​:41 +0000
To​: mjtg@​cus.cam.ac.uk (M.J.T. Guy)
Cc​: perl5-porters@​perl.org
Subject​: Re​: [ID 19991005.003] Floating point error
From​: richard@​rfi.net (Richard Foley)
Message-ID​: <195608280837412609968@​slip139-92-4-218.mu.de.ibm.net>

Amazing. This must be a really early version of perl. No wonder it took
so long to get here.

Richard no doubt had to copy it in from a paper tape.

--
$jhi++; # http​://www.iki.fi/jhi/
  # There is this special biologist word we use for 'stable'.
  # It is 'dead'. -- Jack Cohen

From [Unknown Contact. See original ticket]

Chaim Frenkel writes​:

Date​: Tue, 28 Aug 1956 08​:37​:41 +0000
To​: mjtg@​cus.cam.ac.uk (M.J.T. Guy)
Cc​: perl5-porters@​perl.org
Subject​: Re​: [ID 19991005.003] Floating point error
From​: richard@​rfi.net (Richard Foley)
Message-ID​:
<195608280837412609968@​slip139-92-4-218.mu.de.ibm.net>

Amazing. This must be a really early version of perl. No
wonder it took
so long to get here.

Richard no doubt had to copy it in from a paper tape.

--
$jhi++; # http​://www.iki.fi/jhi/

Actually it took a while to scan, and OCR, it from the slate it was
originally carved on to.

Ciao
Richard Foley

richard@​rfi.net
"Ciao" - (shorter than 'Aufwiedersehen' :-)