Re: [gentoo-dev] euses(1) Reimplementation

[Ashley Dixon]

Hi Fabian, cheers for your response.

On Thu, Jul 09, 2020 at 08:39:30AM +0200, Fabian Groffen wrote:
> Sounds like you've put some work into this.  You could compare against
> `quse -D <flag>` (from portage-utils) as well to get another point of
> measure.

quse is about half as fast as my tool, however  that's  understandable  as  it's
working primarily from ebuild scripts, as opposed to USE-flag descriptors.   The
two tools yield exactly the same results,  providing  that  `-s`  is  passed  to
ash-euses (its default behaviour is to include flag descriptions in the  search;
`-s` instructs it to only display matches which appear as a flag).

The disadvantage of my tool is its inability to understand  the  nature  of  the
packages, such that it cannot offer command-line options such as  "only  display
results related to installed packages".

> I don't know what you did measure euses against though, it seems fairly
> fast to me (env PORTDIR=`q -e PORTDIR` euses -v libressl), is there a
> specific case you're focussing on?

It is very fast, however it could be faster.  I ran  it  through  callgrind  and
kcachegrind to find that it spends over 56% of its  execution  time  on  strncpy
calls; the string-construction is extremely  inefficient.   My  reimplementation
also aims to consist of more maintainable  and  clean  code  (for  example,  the
original tool declares 23 nondescriptly named local  variables  at  the  top  of
main(), and  more  throughout  the  function).   Regardless,  the  obvious  main
advantage is that it is fully compliant with the  repos.conf  syntax,  but  also
works on legacy PORTDIR systems.

As an irrelevant aside, my version  also  uses  the  strcasestr(3)  function  to
perform the case-insensitive search.  Unfortunately, this forces _GNU_SOURCE  to
be defined for the inclusion of `string.h`---however, it is hugely  faster  than
running  tolower(3)  on  every  character  of  the  query  and  buffer,  as  the
canonicalisation  (in  this  case,  converting  the  needle  and   haystack   to
lower-case), is done as part of  the  standard  string-searching  function  call
(`two_way_{long,short}_needle`) [1].  As discussed in my  previous  e-mail,  I'm
working on reimplementing this with the Two-Way algorithm (and shift tables  for
small needles) to avoid the non-standard dependency, although it  might  take  a
few days.

        Ashley.

[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=string/str-two-way.h;h=de247fbc98b83a6e1653288e4161751710d026ce;hb=HEAD#l35

-- 

Ashley Dixon
suugaku.co.uk

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