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Re^2: Confusion about code sample in perlfaq4

by vr (Initiate)
on Feb 22, 2013 at 23:26 UTC ( #1020246=note: print w/ replies, xml ) Need Help??


in reply to Re: Confusion about code sample in perlfaq4
in thread Confusion about code sample in perlfaq4

Thanks for great answers. Maybe, part of my confusion was because first "push" in faq code is unnecessary - why not replacing both lines

push @ints, 0 if $bits =~ s/^(\d)// && $1; push @ints, pos $bits while $bits =~ /1/g;

with

push @ints, pos($bits)-1 while $bits =~ /1/g;

And it's faster, if i'm not mistaken with how i checked it with Benchamrk module.


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Re^3: Confusion about code sample in perlfaq4
by BrowserUk (Pope) on Feb 23, 2013 at 06:25 UTC
    why not replacing both lines

    If you look carefully at the first line, you'll see that in addition to pushing 0 if the first bit(byte!) is set, it also removes the first byte.

    Which means that the second line operates on the string with the first byte removed.

    That's because the value pos returns is the position after where the last match occurred, so by removing the first byte the positions come out correctly.

    Of course, they could have just subtracted 1 from pos, then: a) that first line; b) two visits to the regex engine; and c) modifying the string; become unnecessary.

    But then, if you use the tool perl provides for the job, you not only avoid the regex engine, but also the need to unpack the vector to a string of 1s & 0s:

    print grep vec( pack('V',1431655765), $_, 1), 0 .. 31;; 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 print grep vec( ~pack('V',1431655765), $_, 1), 0 .. 31;; 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

    A very curious FAQ answer.


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