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Re: recent argp changes

From: Bruno Haible
Subject: Re: recent argp changes
Date: Tue, 1 May 2007 22:42:54 +0200
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Hello Sergey,

> The option sorting in argp-help was based on the stability
> of sort algorithm, therefore the test failed on systems with
> quicksort qsort implementations.  It went unnoticed on glibc,
> because its qsort uses adaptive algorithm, defaulting to
> insertion sort if the number of partitions is smaller than a
> predefined value, which happens to be true for the argp tests.

Indeed, with your latest changes, the argp tests pass on:
  - glibc 2.3.6, IRIX 6.5 (where it failed before)
  - MacOS X 10.3.9, OSF/1 4.0d (not tested last time).

> Use argument addresses to ensure they never compare as equal.

However, I think this is not portable. While earlier you were assuming
a stable sorting algorithm, you are now assuming an in-place sorting
algorithm. If a libc were to implement qsort by use of mergesort (and
temporary storage), such a sorting algorithm would pass you two pointers
to hol_entrys in different array. Then HOL_ENTRY_PTRCMP's result depends
on the temporary storage allocation strategy.

To make this portable, I see two options:
  - Sort an array of 'hol_entry*' instead of an array of 'hol_entry';
    then you can be sure the hol_entrys stay in place. Or
  - Add a field 'array_index' to the hol_entry struct. Fill these fields
    right before calling qsort.


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