Re: [PATCH 1/3] compat: add qsort_s()

["René Scharfe" <l.s.r@web.de>]

Am 01.12.2016 um 21:22 schrieb Junio C Hamano:
> Junio C Hamano <gitster@pobox.com> writes:
>
>> Eh, wait.  BSD and Microsoft have paramters reordered in the
>> callback comparison function.  I suspect that would not fly very
>> well.
>
> Hmm.  We could do it like this, which may not be too bad.

It's kinda cool to have a bespoke compatibility layer for major 
platforms, but the more I think about it the less I can answer why we 
would want that.  Safety, reliability and performance can't be good 
reasons -- if our fallback function lacks in these regards then we have 
to improve it in any case.

Text size could be a valid reason, but the full function only adds a bit 
more than 2KB to the unstripped git binary.

The flip side is we'd build an ifdef maze that's harder to read and a 
lot more difficult to test.

What do we get in return for that additional complexity?

> #if APPLE_QSORT_R
> struct apple_qsort_adapter {
> 	int (*user_cmp)(const void *, const void *, void *);
> 	void *user_ctx;
> }
>
> static int apple_qsort_adapter_cmp(void *ctx, const void *a, const void *b)
> {
> 	struct apple_qsort_adapter *wrapper_ctx = ctx;
> 	return wrapper_ctx->user_cmp(a, b, wrapper_ctx->user_ctx);
> }
> #endif
>
> int git_qsort_s(void *b, size_t n, size_t s,
>       	   int (*cmp)(const void *, const void *, void *), void *ctx)
> {
> 	if (!n)
> 		return 0;
> 	if (!b || !cmp)
> 		return -1;
> #if GNU_QSORT_R
> 	qsort_r(b, n, s, cmp, ctx);
> #elif APPLE_QSORT_R
> 	{
> 		struct appple_qsort_adapter a = { cmp, ctx };
> 		qsort_r(b, n, s, &a, appple_qsort_adapter_cmp);
> 	}
> #endif

Nit: The fallback for non-GNU, non-Apple systems is missing here, but 
the idea is illustrated clearly enough.

>       return 0;
> }
>