I find your hashref-checking code quite strange—you are de-referencing (%{$HASH_REF}) a hashref ($HASH_REF), then treating the de-reference as a hash-ref itself ({%{$HASH_REF}}->{$random_number})—which I wouldn't expect to run at all. (UPDATE: kyle explained what I was too sleepy to notice—the extra pair of braces is re-creating a hashref from the de-referenced hashref, and you're then de-referencing it again before checking for existence.) Anyway, it does run, and I also observe a significant slow-down in the second loop, whatever it's doing.

Since I don't know what the second loop is doing, there could be lots of reasons, but one obvious candidate is that indirection has a cost, and all that de-referencing doesn't come for free. Changing the second loop to 

my %HASH_DEREF = %$HASH_REF;
for(...){
    my $random_number = ...;
    1 if exists $HASH_DEREF{$random_number};
}

[download]
gives a running time nearly identical to the first.

In reply to Re: Hash reference searching by JadeNB
in thread Hash reference searching by seggy

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.