You use substr to get 1st char even though ord returns numeric value of 1st char
You use split to get a list of individual characters and throw them away using a slice

  #!/usr/bin/perl -w

  use strict;
  use Benchmark qw(:all);

  my $str_a = "dlajsdlkajslkdjasldjasljdaskjd";

  cmpthese(
    -5,
    {
      'Test1' => sub { ord( $str_a ) },
      'Test2' => sub { ord( ( split ( //, $str_a ) )[0] ) },
      'Test3' => sub { ord( substr $str_a, 0, 1 ) },
    }
  );

__DATA__

Results:
           Rate  Test2  Test3  Test1
Test2    6321/s     --   -99%  -100%
Test3  516114/s  8065%     --   -72%
Test1 1827646/s 28815%   254%     --
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kral,
I think you are misreading something. The first test by far surpassed the other two. In the first test you are using a long string, not a single character.

Additionally, it isn't that ord works better with only one character as an argument - it is that the other two are doing a lot more work. Using substr or split to get the first character is extra operations that are completely un-necessary. The ord function (perldoc -f ord) would work the same if it was a single character or a long string. It is for this reason that the second two tests take more time. They are doing un-necessary work.

I hope this clears things up - L~R

I think you are misreading something. The first test by far surpassed the other two. In the first test you are using a long string, not a single character.

You're right! I have completely misunderstood the test's results. I'm so sorry!

----------
kral
(sorry for my english)