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Re: [PATCH] grub-mkconfig linux: Fix quadratic algorithm for sorting men

From: Oskari Pirhonen
Subject: Re: [PATCH] grub-mkconfig linux: Fix quadratic algorithm for sorting menu items
Date: Tue, 3 May 2022 19:54:51 -0500

On Tue, May 03, 2022 at 07:15:47PM +0200, Mihai Moldovan wrote:
> Just a nit, feel free to ignore it...
> * On 5/3/22 4:42 PM, Mathieu Desnoyers wrote:
> > How does the following paragraph sound ?
> > 
> > ^^^^^^^^
> > Here is the improved algorithm proposed:
> > 
> > - Prepare a list with all the relevant information for ordering by a single
> >   sort(1) execution. This is done by renaming ".old" suffixes by " 1" and
> >   by suffixing all other files with " 2", thus making sure the ".old" 
> > entries
> >   will follow the non-old entries in reverse-sorted-order.
> > - Call version_reverse_sort on the list (sort -r -V): A single execution of
> >   sort(1) will reverse-sort the list in O(n*log(n)) with a merge sort.
> This is correct for GNU coreutils's sort, but nothing (I'm mostly thinking of
> SUS/POSIX here) mandates that the sort utility must either use merge sort or
> have O(n*log(n)) time complexity.
> Given that you're using version sort, which is a GNU extension, it probably
> can't be anything than GNU sort anyway, though, so the point still holds by
> implicity.
> However, this also means that you're adding a hidden dependency upon GNU
> coreutils sort here, which will hit systems traditionally not using the GNU
> userland by default, most prominently BSDs (which, I might add, seem not to 
> use
> GRUB by default and generally either discourage it or have thrown it out of
> their package management systems).

The existing `version_sort()` function in uses the
same logic for detecting the existence of `sort -V` with a fallback to
`sort -n`. I don't think it adds any new hidden dependencies.

    version_sort ()
      case $version_sort_sort_has_v in
          LC_ALL=C sort -V;;
          LC_ALL=C sort -n;;
          if sort -V </dev/null > /dev/null 2>&1; then
            LC_ALL=C sort -V
            LC_ALL=C sort -n

- Oskari

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