SPUG: return value of assignment operator
Michael R. Wolf
MichaelRWolf at att.net
Wed Apr 30 12:51:39 PDT 2008
My results are closer than yours, but contrary to your interpretation,
*both* yours and mine run more iterations per second for the one that relies
on the lvalue. I'm running Perl cygwin on my XP laptop.
Rate increment_separately increment_lhs
increment_separately 4807692/s -- -8%
increment_lhs 5253940/s 9% --
--
Michael R. Wolf
All mammals learn by playing!
MichaelRWolf at att.net
> -----Original Message-----
> From: benrifkah at gmail.com [mailto:benrifkah at gmail.com] On Behalf Of
> BenRifkah Bergsten-Buret
> Sent: Wednesday, April 30, 2008 12:13 PM
> To: Michael R. Wolf
> Cc: spug-list at pm.org
> Subject: Re: SPUG: return value of assignment operator
>
> On Wed, Apr 30, 2008 at 10:50 AM, Michael R. Wolf <MichaelRWolf at att.net>
> wrote:
> > Open questions for discussion:
> > * Where do you rely on assignment returning the LHS?
> > * What definition of "excess" prevents you from using it further?
>
> I haven't used this before but the only place I would consider it is
> in a context where low source code character count is preferred. The
> only such context I can think of is in one liners.
>
> Everywhere else I lean toward explicit behavior for readability.
>
> According to my setup* relying on the returned lvalue is less efficient:
>
> benb at enkidu:~$ cat performance_tuning/lhs.pl
> #!/usr/bin/perl
>
> use strict;
> use Benchmark qw(:all);
>
> my ($x, $y) = (0,1);
>
> cmpthese (9000000, {
> increment_lhs => sub { ($x = $y)++ },
> increment_separately => sub { $x = $y; $x++ },
> });
>
> benb at enkidu:~$ perl performance_tuning/lhs.pl
> Rate increment_separately increment_lhs
> increment_separately 5555556/s -- -28%
> increment_lhs 7758621/s 40% --
>
> Of course Benchmark was only able to give reliable calculations at 90
> million iterations or more.
>
> -- Ben
>
> * perl -V
> Summary of my perl5 (revision 5 version 8 subversion 4) configuration:
> Platform:
> osname=linux, osvers=2.6.15.6, archname=i386-linux-thread-multi
> uname='linux ernie 2.6.15.6 #1 thu mar 16 13:11:55 est 2006 i686
> gnulinux '
> config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN
> -Dcccdlflags=-fPIC -Darchname=i386-linux -Dprefix=/usr
> -Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/lib/perl/5.8
> -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5
> -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local
> -Dsitelib=/usr/local/share/perl/5.8.4
> -Dsitearch=/usr/local/lib/perl/5.8.4 -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 -Uusesfio -Uusenm
> -Duseshrplib -Dlibperl=libperl.so.5.8.4 -Dd_dosuid -des'
> hint=recommended, useposix=true, d_sigaction=define
> usethreads=define use5005threads=undef useithreads=define
> usemultiplicity=define
> useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
> use64bitint=undef use64bitall=undef uselongdouble=undef
> usemymalloc=n, bincompat5005=undef
> Compiler:
> cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS
> -DDEBIAN -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE
> -D_FILE_OFFSET_BITS=64',
> optimize='-O2',
> cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN
> -fno-strict-aliasing -I/usr/local/include'
> ccversion='', gccversion='3.3.5 (Debian 1:3.3.5-13)', gccosandvers=''
> intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
> d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
> ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t',
> lseeksize=8
> alignbytes=4, prototype=define
> Linker and Libraries:
> ld='cc', ldflags =' -L/usr/local/lib'
> libpth=/usr/local/lib /lib /usr/lib
> libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
> perllibs=-ldl -lm -lpthread -lc -lcrypt
> libc=/lib/libc-2.3.2.so, so=so, useshrplib=true,
> libperl=libperl.so.5.8.4
> gnulibc_version='2.3.2'
> Dynamic Linking:
> dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
> cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'
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