Don’t Optimize Code -- Benchmark It
-- from Ten Essential Development Practices by Damian Conway
The real problem is that programmers have spent far too much time worrying about efficiency in the wrong places and at the wrong times;
premature optimization is the root of all evil (or at least most of it) in programming
-- Donald Knuth
Without good design, good algorithms, and complete understanding of the
program's operation, your carefully optimized code will amount to one of
mankind's least fruitful creations -- a fast slow program.
-- Michael Abrash
Wow, I assumed they were complaining about clarity rather than efficiency! :)
For cheap thrills, assuming all you need are the file names 0000 .. 9999 in order,
I benchmarked the three offered solutions as shown below.
use strict;
use warnings;
use Benchmark qw(timethese);
sub orig {
for my $i ( 0 .. 9 ) {
for my $j ( 0 .. 9 ) {
for my $k ( 0 .. 9 ) {
for my $l ( 0 .. 9 ) {
my $filename = "$i$j$k$l";
}
}
}
}
}
sub yourmum {
for ( 0 .. 9999 ) {
my $filename = sprintf "%04d", $_;
}
}
sub marshall {
for ('0000' ... '9999') {
my $filename = $_;
}
}
orig();
yourmum();
marshall();
timethese 50000, {
Orig => sub { orig() },
YourMum => sub { yourmum() },
Marshall => sub { marshall() },
};
On my machine, the results were:
Benchmark: timing 50000 iterations of Marshall, Orig, YourMum...
Marshall: 25 wallclock secs (25.16 usr + 0.00 sys = 25.16 CPU) @ 19
+87.52/s (n=50000)
Orig: 39 wallclock secs (38.83 usr + 0.00 sys = 38.83 CPU) @ 12
+87.73/s (n=50000)
YourMum: 40 wallclock secs (40.08 usr + 0.00 sys = 40.08 CPU) @ 12
+47.57/s (n=50000)
If all you need are the file names (not the individual digits), it's no surprise that
Marshall's suggestion was the fastest. I also think it is the simplest and clearest
if all you need are the file names.
Update: see also perlperf - Perl Performance and Optimization Techniques. Added this node to Performance References.
