updated code:
use Benchmark qw(:all);
my $string =
'zSQ32dfW2Ffc43lOp3fgr5gbaBDCS4REGW4aFAsdSDRsHRJKK32DBSEO0WGNHSGDJR
SSJHSFFSLFSHJHJAMMHBMADBADanhkAdgdDJKJKdfds123243453dsfdge34ldgdbdbkbhggdldjgkdggdH4DBMBHADfsgfJsaJdJSHtSEGkDNGjThWHgFSfJRdWaTGHD8JKHADBHK7HE0WGSF9uSFiKHBhhSafRK5HH1AD3aaAKH9ohWJHdSFuNtSVr9SFSL75GLfJhDAJAEyAfMVjFSk2FDG43F1HBFSFSFSfsdfwe342sfd';
cmpthese(-10, {
old => sub {
my ($entropy, $len, $p, %t) = (0, length($string));
return (map { $p = $_/$len; $entropy -= $p * log $p } (map
{ $t{$_}++ } split '', $string) ? values %t : () and $entropy / log 2);
},
new => sub {
my ($entropy, $len, $p, %t) = (0, length($string));
my @chars = split '', $string;
$t{$_}++ foreach @chars;
foreach (values %t) {
$p = $_/$len;
$entropy -= $p * log $p ;
}
return $entropy / log 2;
},
anew => sub {
my ($entropy, $len, $p, %t) = (0, length($string));
$t{$_}++ foreach split '', $string;
foreach (values %t) {
$p = $_/$len;
$entropy -= $p * log $p ;
}
return $entropy / log 2;
},
});
in which case anew is fastest :)
On Tue, Nov 6, 2018 at 10:24 AM LNATION . <thisusedtobeanemail@gmail.com>
wrote:
Show quoted text> Hey,
>
> can you run the following benchmark and let me know if you get the same
> result as me?
>
> use Benchmark qw(:all);
> my $string =
> 'aBDCS4REGW4aFAsdSDRsHRJKK32DBSEO0WGNHSGDJRSSJHSFFSLFSHJHJAMMHBMADBADanhkAdgdDJKJKdfdggdH4DBMBHADfsgfJsaJdJSHtSEGkDNGjThWHgFSfJRdWaTGHD8JKHADBHK7HE0WGSF9uSFiKHBhhSafRK5HH1AD3aaAKH9ohWJHdSFuNtSVr9SFSL75GLfJhDAJAEyAfMVjFSk2FDG43F1HBFSFSFSfsdfwe342sfd';
> cmpthese(-10, {
> old => sub {
> my ($entropy, $len, $p, %t) = ($string, length($string));
> return (map { $p = $_/$len; $entropy -= $p * log $p } (map {
> $t{$_}++ } split '', $_[0]) ? values %t : () and $entropy / log 2);
> },
> new => sub {
> my ($entropy, $len, $p, %t) = ($string, length($string));
> my @chars = split '', $_[0];
> $t{$_}++ foreach @chars;
>
> foreach (values %t) {
> $p = $_/$len;
> $entropy -= $p * log $p ;
> }
>
> return $entropy / log 2;
> },
> });
>
> [image: Screenshot 2018-11-06 at 10.23.03.png]
>
> On Mon, Nov 5, 2018 at 4:05 PM john via RT <
> bug-Shannon-Entropy@rt.cpan.org> wrote:
>
>> Mon Nov 05 04:05:44 2018: Request 127573 was acted upon.
>> Transaction: Ticket created by john.imrie@oleeo.com
>> Queue: Shannon-Entropy
>> Subject: Speed of execution.
>> Broken in: (no value)
>> Severity: (no value)
>> Owner: Nobody
>> Requestors: john.imrie@oleeo.com
>> Status: new
>> Ticket <URL:
https://rt.cpan.org/Ticket/Display.html?id=127573 >
>>
>>
>> Hi there,
>>
>> This question
>>
https://stackoverflow.com/questions/51624871/calculating-the-entropy-of-a-32mb-file-in-perl-what-is-the-quickest-method/51628560#51628560
>> on Stack Overflow prompted me to rewrite your entropy function
>>
>> According to the person who wrote the original question this version is a
>> significant speed up.
>>
>> Here's the new version in full.
>>
>> sub entropy {
>> my ($entropy, $len, $p, %t) = (0, length($_[0]));
>> my @chars = split '', $_[0];
>> $t{$_}++ foreach @chars;
>>
>> foreach (values %t) {
>> $p = $_/$len;
>> $entropy -= $p * log $p ;
>> }
>>
>> return $entropy / log 2;
>> }
>>
>> John
>>
>
![Mon Nov 05 22:45:45 2018 (21.4k) by thisusedtobeanemail [...] gmail.com](/Ticket/Attachment/1818386/978367/Screenshot%202018-11-06%20at%2010.23.03.png){kind=link}
![Mon Nov 05 22:25:20 2018 (21.4k) by thisusedtobeanemail [...] gmail.com](/Ticket/Attachment/1818380/978358/Screenshot%202018-11-06%20at%2010.23.03.png){kind=link}