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Date: Sun, 8 Aug 2021 21:39:00 +0200
From: Olivier Galibert <galibert@...ox.com>
To: Jon Chesterfield <jonathanchesterfield@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] stdlib: implement qsort_r
I don’t believe in deep inlining in that case, there’s too much recursion.
As for adding overhead to qsort by sharing qsort_r’s code it is indeed
trivial to do but I don’t know whether the tradeoff should be done.
OG.
Le dim. 8 août 2021 à 14:42, Jon Chesterfield <
jonathanchesterfield@...il.com> a écrit :
> On Sun, Aug 8, 2021 at 12:29 PM Olivier Galibert <galibert@...ox.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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