As seen today on fun-with-perl, the code that calculates the next power of two: 

sub next_power_of_two {
    my %s;
    @s{1..shift} = ();
    local $_ = %s;
    return m{/(.*)};
}

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(I've changed the original code a bit to pass "use warnings"), -- so the annual Perl Code Joke prize goes to shmem!

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Re: next power of two
by jmcnamara (Monsignor) on Nov 26, 2007 at 14:47 UTC

    I don't know if it is the original that you refer to but here is a obfu/joke node from 2002 where I use this technique: Power Twool. 
        sub powa2 
    {
    ;      local %_ = @_
    ;      keys  %_ = pop
    ;      $_ =  %_
    ;      split '\/'
    ;      pop
    }

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    --
    John.

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      Well, I have been the poster to fwp... and I looked up your node after I posted (but I definitely knew there must be something around like that in the monastery). Here is the exciting answer from Uri: 
      >>>>> "s" == shmem  <gm@cruft.de> writes:


  s> You forgot an obscure corner of hashes: hashes in scalar context.
  s> Here's a a use - calculate the next power of 2 of a given number:

  s> sub next_power_of_two {
  s>     my %s;
  s>     @s{1..shift} = ();
  s>     %s =~ '/';
  s>     return $';
  s> }

  s> ;-)

GACK!!!

and that assume knowledge of the internals of hashes. not a good thing
to teach! :)

uri

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      but your version is much more elegant, except perhaps the %s =~ '/' thingy ;-D

      update: and I posted it only because the discussion went into discussing the pros and cons of dispatch tables, oo, inheritance etc pp... in short, to introduce some fun again ;-)

      --shmem 

      _($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}
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Re: next power of two
by ikegami (Patriarch) on Nov 26, 2007 at 15:50 UTC

    It always returns 1 for me, unless you intend for your function to be called in list context. And since local $_ is buggy, you'd be best off avoid it. 

    sub next_power_of_two {
    my %s;
    @s{1..shift} = ();
    return %s =~ m{/(.*)} && $1;
}

    [download]

    Update: Added local $_ fix.

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Re: next power of two
by Anonymous Monk on Nov 26, 2007 at 13:07 UTC
    My perl uses 8 as the minimum number of buckets, so it's incorrect for values which are less than 4.
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Re: next power of two
by trizen (Hermit) on Sep 11, 2011 at 10:54 UTC
    Or a faster version without using any regexp 
    sub next_power_of_two ($) {
    my %s;
    @s{1..$_[0]} = ();
    return substr(%s,1+index(%s,'/'));
}

print next_power_of_two(257);

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[d/l]

      About 50x faster still :)

      sub b{
    my %s;
    keys %s = shift; 
    undef $s{1};
    substr %s, 1+index( %s,'/' );
}

      [download]
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
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        ...and here is the fastest :-)

        sub next_power_of_two {2 << log($_[0]) / log(2)}
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Re: next power of two
by JavaFan (Canon) on Sep 11, 2011 at 15:15 UTC
    Hmmm, doesn't always work: 
      $ perl -wE '@h{1..shift}=(); say scalar %h;' 16384
  12812/32768
  $ perl -wE '@h{1..shift}=(); say scalar %h;' 32768
  20636/32768

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