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From: Jon Chesterfield <jonathanchesterfield@gmail.com>
To: musl@lists.openwall.com
Cc: Olivier Galibert <galibert@pobox.com>
Subject: Re: [musl] [PATCH] stdlib: implement qsort_r
Date: Sun, 8 Aug 2021 13:42:27 +0100	[thread overview]
Message-ID: <CAOUYtQBSpJf-QnXpAKZQJk9E=Lx3SRxOjk-r3gm_8JnxEj7NSQ@mail.gmail.com> (raw)
In-Reply-To: <20210808112612.44230-1-galibert@pobox.com>

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On Sun, Aug 8, 2021 at 12:29 PM Olivier Galibert <galibert@pobox.com> wrote:

> The extension qsort_r allows calling qsort on a list of indices
> without having a global variable to hold the data to sort.
>

qsort_r is a strong improvement on qsort. I think it's available outside of
glibc.

I remember doing something similar locally. Just looked it up and I
renamed & mutated qsort to pass the context along. Therefore typed into
email, I think something like this would provide an implementation of
qsort in terms of qsort_r.

// declare qsort_r
typedef int (*cmp_r_t)(const void *, const void *, void * context);


void qsort_r(void *base, size_t nel, size_t width, cmp_r_t cmp, void*
context);


// pass it a function that extracts the comparator for qsort from the
// context
typedef int (*cmp_t)(const void *, const void *);


static int compare_adapter(const void *l, const void *r, void * context)
{
  cmpt_t c = (cmpt_t) context;


  return c(l,r);


}

// tail call
void qsort(void *base, size_t nel, size_t width, cmp_t c)
{
  return qsort_r(base, nel, width, compare_adapter, (cmp_t_t)c);


}

Given optimism about inlining or an always inline annotation
it should turn into the same machine code as the macro
instantiation approach. Alternatively it's a tail call into qsort_r, so
a couple of indirections in exchange for minimal code size growth.

I haven't compiled or tested that (or looked up the coding conventions
for musl) so this is a drive by suggestion, written in pseudocode
instead of prose for clarity.

Thanks all!

Jon

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  reply	other threads:[~2021-08-08 12:42 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-08 11:26 Olivier Galibert
2021-08-08 12:42 ` Jon Chesterfield [this message]
2021-08-08 19:39   ` Olivier Galibert
2021-08-08 20:35   ` Érico Nogueira
2021-08-08 21:21     ` Jon Chesterfield
2021-08-08 23:05       ` Rich Felker
2021-08-09  6:03         ` Olivier Galibert
2021-08-09 17:27   ` Florian Weimer
2021-08-08 20:28 ` Érico Nogueira
2021-08-18 17:36 Olivier Galibert
2021-08-18 20:18 ` Rich Felker

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