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### Re: Re: Re: eq vs. ==

by giulienk (Curate)
 on Jul 21, 2003 at 13:04 UTC ( #276250=note: print w/replies, xml ) Need Help??

in reply to Re: Re: eq vs. ==

Actually i think i read it in Mastering Algorithms with Perl even though i cannot find it right now.

Anyway to wipe out your doubts you can try a benchmark:

#!/usr/bin/perl

use strict;
use Benchmark qw(:all);

cmpthese(10, {
'eq'    =>  sub {
for (my ($i,$j) = (0, 0); $i < 1_000_000;$i++) {
$j++ if ($i % 3) eq 2;
}
},
'=='    =>  sub {
for (my ($i,$j) = (0, 0); $i < 1_000_000;$i++) {
$j++ if ($i % 3) == 2;
}
},
});

__END__
Benchmark: timing 10 iterations of ==, eq...
==: 28 wallclock secs (27.91 usr +  0.00 sys = 27.91 CPU) @  0
+.36/s (n=10)
eq: 36 wallclock secs (36.16 usr +  0.01 sys = 36.17 CPU) @  0
+.28/s (n=10)
s/iter   eq   ==
eq   3.62   -- -23%
==   2.79  30%   --
[download]
The test was run on my Powerbook G3 with Perl v5.8.0 built for powerpc-linux-thread-multi.

I agree we shouldn't program for speed only, but here speed and good form comes from the same expression. Also you may note how my first post in this thread started out with "Also": it wasn't meant to be a comprehensive response to c's problem, but instead my 2 cents to what already said.

$|=$_="1g2i1u1l2i4e2n0k",map{print"\7",chop;select$,,$,,$,,$_/7}m{..}g

Replies are listed 'Best First'.
Re: eq vs. ==
by Abigail-II (Bishop) on Jul 21, 2003 at 13:45 UTC
Was your point trying to prove chromatics point? Because IMO, all your benchmark shows is that having to do an atoi takes time. Because in both tests, the left hand side of the operator is the outcome of a module operation, the %. And that's numeric.

Here's a different benchmark. One that used both numbers and string, and both == and eq. You will see that the fastest cases are when no conversions needs to take place. Conclusion: use eq when comparing strings, and == when comparing numbers if speed is your main motivation.

#!/usr/bin/perl

use strict;
use warnings;
use Benchmark qw /cmpthese/;

our ($a,$b, $c,$d);

cmpthese -10 => {
'==-num' => '$::a = 0; for my$i (0 .. 1000000) {
$::a ++ if$i == 100;
}',
'eq-num' => '$::b = 0; for my$i (0 .. 1000000) {
$::b ++ if$i eq "100";
}',
'==-str' => '$::c = 0; for my$i ("0" .. "1000000") {
$::c ++ if$i == 100;
}',
'eq-str' => '$::d = 0; for my$i (0 .. "1000000") {
$::d ++ if$i eq "100";
}',
};

print "[$a] [$b] [$c] [$d]\n";

__END__
Benchmark: running ==-num, ==-str, eq-num, eq-str, each for at least 1
+0 CPU seconds...
==-num: 10 wallclock secs (10.02 usr +  0.00 sys = 10.02 CPU) @  4
+.19/s (n=42)
==-str: 10 wallclock secs (10.25 usr +  0.01 sys = 10.26 CPU) @  1
+.75/s (n=18)
eq-num: 10 wallclock secs (10.06 usr +  0.01 sys = 10.07 CPU) @  2
+.38/s (n=24)
eq-str: 10 wallclock secs (10.28 usr +  0.00 sys = 10.28 CPU) @  2
+.43/s (n=25)
Rate ==-str eq-num eq-str ==-num
==-str 1.75/s     --   -26%   -28%   -58%
eq-num 2.38/s    36%     --    -2%   -43%
eq-str 2.43/s    39%     2%     --   -42%
==-num 4.19/s   139%    76%    72%     --
[1] [1] [1] [1]
[download]

Abigail

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