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Re: [PATCH] Simplify strncat.
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: Wilco Dijkstra <wdijkstr at arm dot com>, 'OndÅej BÃlka' <neleai at seznam dot cz>, eggert at cs dot ucla dot edu
- Cc: libc-alpha at sourceware dot org
- Date: Fri, 19 Dec 2014 03:22:05 -0500
- Subject: Re: [PATCH] Simplify strncat.
- Authentication-results: sourceware.org; auth=none
- References: <000f01d01ad0$17e381d0$47aa8570$ at com>
On 12/18/2014 09:37 AM, Wilco Dijkstra wrote:
> OndÅej BÃlka wrote:
>>> On Tue, Dec 16, 2014 at 12:50:38PM -0800, Paul Eggert wrote:
>>> Thanks, this is much better than worrying about how to pacify GCC.
>>> The code could be made a bit shorter and clearer with mempcpy, and
>>> there's no longer any need to distinguish between s and s1, so I
>>> suggest the following minor rewrite, which shrinks the code size by
>>> another 26 bytes (16%) on my x86-64 platform.
>>> char *
>>> STRNCAT (char *s1, const char *s2, size_t n)
>>> char *s1_end = mempcpy (s1 + strlen (s1), s2, __strnlen (s2, n));
>>> *s1_end = '\0';
>>> return s1;
>> That looks better (with minor fix s/mempcpy/__mempcpy/), anybody objects
>> using this instead?
> I don't think mempcpy is better, few targets define it (ARM, MIPS, AARCH64
> don't for example), so it means an extra call and return. Mempcpy is also
> non-standard and rarely used, so would not be cache resident even if you
> have an optimized implementation.
> This has the same advantages as Paul's version (fewer callee-saves):
> char *
> STRNCAT (char *s1, const char *s2, size_t n)
> char *s;
> n = strnlen (s2, n);
> s = s1 + strlen (s1);
> s[n] = '\0';
> memcpy (s, s2, n);
> return s1;