Re: [PATCH] Simplify strncat.

["Carlos O'Donell" <carlos at redhat dot 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;
> }

Agreed.

Cheers,
Carlos.