On Wed, Jun 1, 2011 at 19:02, Ronald J Kimball <[email protected]> wrote:
> On Wed, Jun 01, 2011 at 02:36:40PM +0100, Paul Makepeace wrote:
>> On Tue, May 31, 2011 at 22:41, Nick Patch <[email protected]> wrote:
>> > use Benchmark qw( cmpthese );
>> >
>> > cmpthese(-2, {
>> > assign => sub { my $x = 'bar'; $x = "foo/$x" },
>> > substr => sub { my $x = 'bar'; substr $x, 0, 0, 'foo/' },
>> > lvalue => sub { my $x = 'bar'; substr($x, 0, 0) = 'foo/' },
>> > });
>>
>> Oddly(?) join() is 20% faster than assignment:
>>
>> ...
>> join => sub { my $x = 'bar'; $x = join('/', 'foo', 'bar') },
>> oooscf => sub { my $x = 'bar'; $x = File::Spec->catfile($x, 'bar') },
>> fnoscf => sub { my $x = 'bar'; $x = catfile($x, 'bar') },
>
> You're not benchmarking the right behavior. In particular, your join sub
> is not using $x in the call to join.
>
> join => sub { my $x = 'bar'; $x = join('/', 'foo', $x) },
> oooscf => sub { my $x = 'bar'; $x = File::Spec->catfile('foo', $x) },
> fnoscf => sub { my $x = 'bar'; $x = catfile('foo', $x) },
Yes, sorry, code paste fail. The results paste was right though :)
As penance, here's an exploration of O(n) versus, er, not...
Do the benchmarks but with a repetition which mirrors how larger
output in general is built. *join is the only one that's linear*, and
substr, while the winner on smaller n, takes a severe beating as the
string length goes up. The naive assignment sucks but not as horribly.
#!/usr/bin/perl
use Benchmark qw( cmpthese );
use Devel::Leak;
use File::Spec;
use File::Spec::Functions;
sub concat_bm {
my $count = shift;
cmpthese(-2, {
assign => sub { my $x = 'bar'; for (1..$count) { $x = "foo/$x" } },
substr => sub { my $x = 'bar'; for (1..$count) { substr $x, 0,
0, 'foo/' } },
lvalue => sub { my $x = 'bar'; for (1..$count) { substr($x, 0,
0) = 'foo/' } },
join => sub { my $x = 'bar'; my @foos = ('foo') x $count; {
$x = join('/', @foos, $x) } },
});
}
my $count = Devel::Leak::NoteSV($handle);
concat_bm(10);
concat_bm(100);
concat_bm(1000);
concat_bm(10000);
Devel::Leak::CheckSV($handle);
Rate lvalue assign join substr
lvalue 311229/s -- -3% -32% -41%
assign 321920/s 3% -- -30% -39%
join 458335/s 47% 42% -- -13%
substr 526317/s 69% 63% 15% --
Rate lvalue assign substr join
lvalue 26302/s -- -11% -30% -55%
assign 29466/s 12% -- -22% -49%
substr 37574/s 43% 28% -- -35%
join 57931/s 120% 97% 54% --
Rate lvalue substr assign join
lvalue 660/s -- -7% -56% -89%
substr 710/s 8% -- -52% -88%
assign 1490/s 126% 110% -- -75%
join 6002/s 809% 746% 303% --
Rate lvalue substr assign join
lvalue 7.73/s -- -0% -67% -99%
substr 7.73/s 0% -- -67% -99%
assign 23.3/s 202% 202% -- -96%
join 570/s 7270% 7270% 2341% --
Paul
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