in reply to Silly question about function args

According to Benchmark the first form is very slightly faster, but probably not enough to make much of a difference. 
use Benchmark qw/cmpthese/;

sub s1 {my ($arg1, $arg2, $arg3) = @_;}; 
sub s2 { my $arg1 = shift; my $arg2 = shift; my $arg3 = shift; }

cmpthese(200000, {
shift  => ' { s2(1,2,3) }',
list  => ' {s1(1,2,3)}',
})


Benchmark: timing 200000 iterations of list, shift...
      list:  3 wallclock secs ( 2.14 usr +  0.01 sys =  2.15 CPU) @ 93
+023.26/s (n=200000)
     shift:  2 wallclock secs ( 2.25 usr +  0.02 sys =  2.27 CPU) @ 88
+105.73/s (n=200000)
         Rate shift  list
shift 88106/s    --   -5%
list  93023/s    6%    --

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Re: Re: Silly question about function args
by integral (Hermit) on Feb 09, 2003 at 09:46 UTC
    The fastest way to pass arguments is not to copy them at all, and to access them inplace in @_. (This of course doesn't make readable code). The test case below illustrates this poorly for a simplified function.

    Update: BrowserUk's answer demonstrates this better.

    use Benchmark qw/cmpthese/;
 
sub s1 {my ($arg1, $arg2, $arg3) = @_; $arg+$arg2+$arg3 };
sub s2 { my $arg1 = shift; my $arg2 = shift; my $arg3 = shift; $arg1+$
+arg2+$arg3}
sub s3 {$_[0] + $_[1] + $_[2] }
 
cmpthese(200000, {
    shift  => ' { s2(1,2,3) }',
    list  => ' {s1(1,2,3)}',
    none  => ' {s3(1,2,3)}',
  })

Benchmark: timing 200000 iterations of list, none, shift...
      list:  4 wallclock secs ( 1.39 usr +  0.00 sys =  1.39 CPU) @ 14
+3884.89/s (n=200000)
      none:  1 wallclock secs ( 0.70 usr +  0.01 sys =  0.71 CPU) @ 28
+1690.14/s (n=200000)
     shift:  2 wallclock secs ( 1.46 usr +  0.03 sys =  1.49 CPU) @ 13
+4228.19/s (n=200000)
          Rate shift  list  none
shift 134228/s    --   -7%  -52%
list  143885/s    7%    --  -49%
none  281690/s  110%   96%    --

    [download]

    --
integral, resident of freenode's #perl
[reply]
[d/l]
      The fastest way to pass arguments is not to copy them at all

      Exactly. Inline the function entirely. Thats much faster.

      and to access them inplace in @_

      Persoanlly I would caution against this. An innocuous change of 

      my $foo=shift;
$foo=~s/A.//g;
# to
$_[0]=~s/A.//g;

      [download]
      Would alter the original variable. Better to do away with the subroutine entirely. Then at least this effect is obvious and as I said you avoid the subroutine jump overhead.

      --- demerphq
      my friends call me, usually because I'm late....

[reply]
[d/l]

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