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[perl #109542] $1 handled differently in integer arithmetics

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From:
perlbug . dttn @ manchmal . in-ulm . de
Date:
February 1, 2012 07:16
Subject:
[perl #109542] $1 handled differently in integer arithmetics
Message ID:
rt-3.6.HEAD-14510-1328080824-600.109542-75-0@perl.org
# New Ticket Created by  perlbug.dttn@manchmal.in-ulm.de 
# Please include the string:  [perl #109542]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org:443/rt3/Ticket/Display.html?id=109542 >



This is a bug report for perl from perlbug.dttn@manchmal.in-ulm.de,
generated with the help of perlbug 1.39 running under perl 5.14.2.


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

Hi .,

Still not sure whether this is a bug, so I'd call it surprising.

Using a regular expression to capture a sequence of digits puts
something into $1 that behaves differently when used for further
integer arithmetics. Basically, the reproducer is as follows:

 perl -e '$s = "976562500000"; $s =~ /(\d+)/; printf "%s = %s\n", ($1 * 1024), int ($1 * 1024)'

Expected (at least on amd64):

 1000000000000000 = 1000000000000000

Got:

 1e+15 = 1000000000000000

The surprising thing is this does _not_ happen with named capture
buffers:

 perl -E '$s = "976562500000"; $s =~ /(?<match>\d+)/; printf "%s = %s\n", ($+{match} * 1024), int ($+{match} * 1024)'

Nor after copying $1 into another variable:

 perl -e '$s = "976562500000"; $s =~ /(\d+)/; $t = $1; printf "%s = %s\n", ($t * 1024), int ($t * 1024)'

It appears using $1 switches computation to floating point even the
numbers used are still in the integer range. Care to take a look into
that?

See also http://munin-monitoring.org/ticket/1195 for a case where this
issue causes unwanted effects in the wild.

Regards,

    Christoph Biedl <perlbug.dttn@manchmal.in-ulm.de>

-----------------------------------------------------------------
---
Flags:
    category=core
    severity=low
---
Site configuration information for perl 5.14.2:

Configured by Debian Project at Mon Nov 28 23:30:36 UTC 2011.

Summary of my perl5 (revision 5 version 14 subversion 2) configuration:
   
  Platform:
    osname=linux, osvers=2.6.32-5-amd64, archname=x86_64-linux-gnu-thread-multi
    uname='linux brahms 2.6.32-5-amd64 #1 smp thu nov 3 03:41:26 utc 2011 x86_64 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.14 -Darchlib=/usr/lib/perl/5.14 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.14.2 -Dsitearch=/usr/local/lib/perl/5.14.2 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Duse64bitint -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -Ui_libutil -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.14.2 -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 -fstack-protector -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 -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.6.2', 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 =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib /usr/lib
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=, so=so, useshrplib=true, libperl=libperl.so.5.14.2
    gnulibc_version='2.13'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib -fstack-protector'

Locally applied patches:
    

---
@INC for perl 5.14.2:
    /etc/perl
    /usr/local/lib/perl/5.14.2
    /usr/local/share/perl/5.14.2
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.14
    /usr/share/perl/5.14
    /usr/local/lib/site_perl
    .

---
Environment for perl 5.14.2:
    HOME=/home/cbiedl
    LANG=de_DE.UTF-8
    LANGUAGE (unset)
    LC_MESSAGES=C
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/bash


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