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Re^2: Alternative to bytes::length()

by creamygoodness (Curate)
on Dec 23, 2009 at 01:54 UTC ( #814040=note: print w/ replies, xml ) Need Help??


in reply to Re: Alternative to bytes::length()
in thread Alternative to bytes::length()

Seems like ne "" is what I was looking for. :)

The !! construct won't work because certain strings with lengths can be false:

marvin@smokey:~ $ perl -le 'print "true" if !!"0";' marvin@smokey:~ $ perl -le 'print "true" if !!"1";' true

What did you mean by "premature", though?


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Re^3: Alternative to bytes::length()
by BrowserUk (Pope) on Dec 23, 2009 at 06:16 UTC
    Seems like ne "" is what I was looking for. :)

    Be careful. Anonymonk's benchmark is conflating an aweful lot of other stuff in with the actual code you are concerned about.

    I believe (but I'm open to correction), this to be a far better benchmark, and it shows a radically different result. It might just set your mind at ease. (Or not!):

    #!/usr/bin/perl -- use strict; use warnings; use Benchmark qw( cmpthese ); # Make bytes:: functions available, but use character semantics. use bytes (); our $smileys = "\x{263a}" x 10_000; our $empty = "\x{263a}"; chop $empty; cmpthese -1, { bytes => q{ my $c=0; ( bytes::length($empty) or bytes::length($smileys) ) and ++$c +for 1 .. 1000; }, utf8 => q{ my $c=0; ( length($empty) or length($smileys) ) and ++$c for 1 .. 1000; }, ord => q{ my $c=0; ( ord( $empty ) or ord( $smileys ) ) and ++$c for 1 .. 1000; }, 'ne""' => q{ my $c=0; ( $empty ne '' or $smileys ne '' ) and ++$c for 1 .. 1000; }, }; __END__ C:\test>junk8 Rate bytes ord ne"" utf8 bytes 1379/s -- -72% -75% -76% ord 4992/s 262% -- -10% -13% ne"" 5566/s 304% 12% -- -3% utf8 5757/s 317% 15% 3% --

    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.

      I believe that your 'utf8' case is mostly benchmarking the pulling out of the character count cached in the magic, thus completely missing the original problem. Even if it weren't, I don't see how your benchmark provides any justification for not using eq '' (which perhaps you weren't trying to imply).

      - tye        

        I believe that your 'utf8' case is mostly benchmarking the pulling out of the character count cached in the magic, thus completely missing the original problem.

        I was mostly concerned with pointing out that it's important to consider exactly what you're benchmarking.

        I'm also not convinced that there is enough of a description of "the original problem" to say whether I missed or not. I'm finding it quite hard to think of an application where the time taken to obtain the length of a string would be very significant?

        Except maybe when sorting strings by length, at which point the caching would pretty much negate the first-time cost.

        I don't see how your benchmark provides any justification for not using eq ''

        Um...cos I modified the original benchmark and didn't think about it. Having just swapped the 'ne's for 'eq's, it does make a suprising difference. Though I haven't thought through whether that's down the efficiency of the operator or the change to the boolean logic.

        It did surprise me greatly that ord worked out much faster than bytes::length.


        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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