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Re: regrepeat()

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January 1, 2018 18:08
Re: regrepeat()
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On 31 December 2017 at 22:36, Karl Williamson <> wrote:
> This function is called during regular expression pattern matching for
> things like
>  (foo)+
> to  match as many 'foo's as there are.  There is special code to handle the
> case where foo is a single byte, such as in
>  a+
> It turns out that these cases can be sped up dramatically if what we are
> matching is a long string of 'a's in a row.  We simply load a word with 4 or
> 8 a's and look at the string a word-at-a-time, which uses 1/4 or 1/8 the
> number of instructions.  By using a mask, this can be extended to work for
>  [aA]+
> as well.  The code in each case is just over 20 lines of C.
> My question is, does this happen often enough in real life to justify the
> extra code?
> Leon pointed out that in DNA, there may be longish strings of 'A's.

I think this is highly likely to be worth it.


perl -Mre=debug -e "/just|another|perl|hacker/"

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