in reply to Re: slow CGI's
in thread slow CGI's

I downvoted this node because I think it is an inappropriate suggestion. Rule #1 of benchmarking is don't guess. Rule #2 of benchmarking is optimize what really matters.

The biggest potential problem I can see with this code (without seeing the data set) is that the loop tends to O(n/2) performance. If there are a lot of numbers in the array, it will take a while to find the right number. A hash lookup, tending to O(1) performance, would be much more performant.

Replies are listed 'Best First'.
Re: Re: Re: slow CGI's
by saintbrie (Scribe) on Jul 08, 2003 at 04:25 UTC
    Interestingly, benchmarks do not bear this assumption out. (perl 5.8.0 on a celeron lots of other stuff going on at the same time, but tried multiple times, very similar results). 
    #!/usr/local/bin/perl
use Benchmark;


for (1.. 100000) {
  $rand = rand * 100;
  push @rvs, $rand;
  $last = $rand;
}
$array[0] = $rand;

timethese ( 100, {grepit => \&grepit,
           hashit => \&hashit});

sub grepit {
  return 1 if (grep /$array[0]/, @rvs);

}

sub hashit {
  @hash{@rvs} = (1) x @rvs;
  return 1 if ($hash{$array[0]});
}

    [download]
    Benchmark: timing 100 iterations of grepit, hashit...
    grepit: 19 wallclock secs 
       (19.36 usr +  0.03 sys = 19.39 CPU) @  5.16/s (n=100)
    hashit: 28 wallclock secs 
       (27.84 usr +  0.04 sys = 27.88 CPU) @  3.59/s (n=100)
the number is 0.359661571026372
Grepit found the number
Hashit found the number

    [download]
[reply]
[d/l]
[select]

In Section Seekers of Perl Wisdom