You should always be very suspicious if your benchmark shows results
of 8823529.41 runs/second. Specially when it comes to non-trivial tasks
like sprintf() - after all, than requires perl to parse a format.
Another thing that should ring loud bells is that you are doing sprintf()
in void context. That's not a natural operation. Perhaps Perl optimizes
that away for you - totally screwing up your benchmark. It's a simple test:
$ perl -MO=Deparse -wce 'sprintf "%x%x%x", ord ("a"), ord ("b"), o
+rd ("c")'
Useless use of a constant in void context at -e line 1.
BEGIN { $^W = 1; }
'???';
-e syntax OK
$
Indeed, you just benchmarked how fast perl can do an empty loop.
Not very useful. Your benchmark should include assigning the result
to a variable. So, you might want to do:
#!/usr/bin/perl
use strict;
use warnings 'all';
use Benchmark;
timethese -10 => {
unpack => '$_ = unpack "H*" => "abc"',
sprintf => '$_ = sprintf "%x%x%x", ord ("a"), ord ("b"), ord (
+"c")',
}
__END__
Benchmark: running sprintf, unpack for at least 10 CPU seconds...
sprintf: 11 wallclock secs (10.25 usr + 0.00 sys = 10.25 CPU) @ 77
+5053.56/s (n=7944299)
unpack: 11 wallclock secs (10.48 usr + 0.01 sys = 10.49 CPU) @ 33
+1145.09/s (n=3473712)
It looks like sprintf is still a winner. But is it? Let's
check the deparser again:
$ perl -MO=Deparse -wce '$_ = sprintf "%x%x%x", ord "a", ord "b",
+ord "c"'
BEGIN { $^W = 1; }
$_ = '616263';
-e syntax OK
$
Oops. Perl is so smart, it figured out at compile time the result of the
sprintf. We'd have to make the arguments of sprintf
variable to make Perl actually do work at run time:
$ perl -MO=Deparse -wce '($a, $b, $c) = split // => "abc";
$_ = sprintf "%x%x%x", ord $a, ord $b, ord $c'
BEGIN { $^W = 1; }
($a, $b, $c) = split(//, 'abc', 4);
$_ = sprintf('%x%x%x', ord $a, ord $b, ord $c);
-e syntax OK
$
And only now we can run a fair benchmark:
#!/usr/bin/perl
use strict;
use warnings 'all';
use Benchmark;
use vars qw /$a $b $c $abc/;
$abc = "abc";
($a, $b, $c) = split // => $abc;
timethese -10 => {
unpack => '$_ = unpack "H*" => $::abc',
sprintf => '$_ = sprintf "%x%x%x", ord $::a, ord $::b, ord $::
+c',
}
__END__
Benchmark: running sprintf, unpack for at least 10 CPU seconds...
sprintf: 11 wallclock secs (10.51 usr + 0.01 sys = 10.52 CPU) @ 20
+8379.75/s (n=2192155)
unpack: 10 wallclock secs (10.10 usr + 0.00 sys = 10.10 CPU) @ 32
+3836.04/s (n=3270744)
And guess what? unpack is the winner!
The moral: no benchmark is better than a bad benchmark.
Abigail
| 