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Subject: Re: cygwin qsort erratic
To: Kurt-Karen Carlson-Lougheed <denalisun907 AT gmail DOT com>, cygwin AT cygwin DOT com
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From: Thomas Wolff <towo AT towo DOT net>
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Date: Wed, 2 Sep 2020 09:23:27 +0200
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Am 02.09.2020 um 02:26 schrieb Kurt-Karen Carlson-Lougheed:
> Thomas:
> As stated, twice, the full code is on SourceForge as uac19 v3.3. If 
> you need me to send you a tgz with sample data please let me know, but 
> note the comments and patch below. I can certainly walk you through 
> reproducing the problem if you believe that is worthwhile.
Kurt-Karen:
I am not uac savvy. The proposal to dig out some software package, build 
it (which may create hours-long trouble in some cases), collect data 
from somewhere else etc, to reproduce an assumed bug, is not 
appropriate. It's your term to provide a single, reproducible 
demonstration of a bug. If this were an issue in my project, I would 
close it now for refusal of cooperation.

>
> Stephen:
> Thank you. I couldn't get the 'blame' to work (I am not git savvy), 
> but I got the cygwin qsort.c. The problem is *EXACTLY* as described by 
> Dennis de Champeaux in the 2015-01-11 cygwin list posting. The 
> secondary insertion sort attempt is not safe. I patched as follows, 
> the de Champeaux is code is more correct in removing swap_cnt as it is 
> no longer used:
>
> kc: diff -u qsort.c cygsort.c
> --- qsort.c     2020-09-01 15:36:39.716029300 -0700
> +++ cygsort.c   2020-09-01 16:47:30.152545600 -0700
> @@ -252,14 +252,15 @@
>                 pb += es;
>                 pc -= es;
>         }
> -       if (swap_cnt == 0) {  /* Switch to insertion sort */
> +/* kc
> +       if (swap_cnt == 0) {  // Switch to insertion sort
>                 for (pm = (char *) a + es; pm < (char *) a + n * es; 
> pm += es)
>                         for (pl = pm; pl > (char *) a && CMP(thunk, pl 
> - es, pl) > 0;
>                              pl -= es)
>                                 swap(pl, pl - es);
>                 goto pop;
>         }
> -
> +kc */
>         /*
>          * Rearrange the array in three parts sorted like this:
>          * { elements < pivot, elements == pivot, elements > pivot }
>
> If you need me to provide further information, please advise.
> Regards, kurt
>
> On Tue, Sep 1, 2020 at 3:02 PM Thomas Wolff <towo AT towo DOT net 
> <mailto:towo AT towo DOT net>> wrote:
>
>     Am 01.09.2020 um 22:29 schrieb Kurt-Karen Carlson-Lougheed via Cygwin:
>     >    Brian:
>     > 1. The Qsort() source I sent was from netbsd.org
>     <http://netbsd.org>, NOT cygwin. netbsd works.
>     > 2. Complete package is on SourceForge as uac19 v3.3. I'm happy
>     to send a
>     > tgz if you prefer that. Read 3 choices at end before considering
>     this.
>     > 3. Data is curl'd from owid as shown in the script example.
>     Likewise I can
>     > send a sample data set. The program analyzes COVID-19 csv files
>     from either
>     > owid or github/nytimes
>     > 4. I've used qsort() for years. I agree, keeping the sort
>     routines simple
>     > is always appropriate. I confirmed today the only ones that fail
>     include
>     > float divides, lDsort() and lXsort() in attached c19sort.c. When
>     it's
>     > pre-calculated and added to the struct it works, the code has a
>     toggle now
>     > for testing that.
>     >
>     > Thomas:
>     > I tried (again) today  to build a simple test case. The data
>     structures in
>     > use are complex, probably the only thing I can attempt is
>     stripping down
>     > the code which will be very time consuming. I know you don't
>     know me at
>     > all, but I've written code, debugged proprietary operating systems
>     > (assembler), performed OS dump analysis, troubleshot
>     intermittent hardware
>     > issues, identified disk firmware issues causing intermittent data
>     > corruption, identified nfs performance issues, managed large hpc
>     clusters,
>     > etc. etc. etc. over 40+ years.
>     Your code does not even compile. I did not ask for a minimal test
>     case
>     although that is generally appreciated. But a working test case at
>     least
>     is required to establlish your claim of a bug.
>     >
>     > I see three choices:
>     > A. One of you look at simple the qqsort wrapper. I modified my
>     code to
>     > toggle between the functional netbsd Qsort() and cygwin qsort().
>     I have
>     > demonstrated erroneous results coming from the cygwin version in
>     a small
>     > percentage of requests. If you can acknowledge that, perhaps you
>     can check
>     > the cygwin version of qsort() vs. the current netbsd.org
>     <http://netbsd.org>?
>     > B. If you could kindly provide me or point me to the cygwin
>     qsort() source
>     > I'll check it out myself.
>     > C. We can thank each other and leave cygwin's qsort() as is
>     broken in some
>     > small number of circumstances since I've compiled netbsd's into
>     my code and
>     > that always works.
>     >
>     > Regards, kurt
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