Re: [PATCH 5/7] wcsmbs: optimize wcsncat

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

If no one opposes it, I will commit this shortly.

On 06/02/2019 12:58, Adhemerval Zanella wrote:
> This patch rewrites wcsncat using wcslen, wcsnlen, and wmemcpy.  This is
> similar to the optimization done on strncat by 3eb38795db and e80514b5a8.
> 
> Checked on x86_64-linux-gnu.
> 
> 	* wcsmbs/wcsncat.c (wcsncat): Rewrite using wcslen, wcsnlen, and
> 	wmemcpy.
> ---
>  wcsmbs/wcsncat.c | 53 +++++++-----------------------------------------
>  1 file changed, 7 insertions(+), 46 deletions(-)
> 
> diff --git a/wcsmbs/wcsncat.c b/wcsmbs/wcsncat.c
> index 65e9b226c6..cb6fe71e19 100644
> --- a/wcsmbs/wcsncat.c
> +++ b/wcsmbs/wcsncat.c
> @@ -26,54 +26,15 @@
>  wchar_t *
>  WCSNCAT (wchar_t *dest, const wchar_t *src, size_t n)
>  {
> -  wchar_t c;
> -  wchar_t * const s = dest;
> +  wchar_t *ret = dest;
>  
> -  /* Find the end of DEST.  */
> -  do
> -    c = *dest++;
> -  while (c != L'\0');
> +  /* Find the end of dest.  */
> +  dest += __wcslen (dest);
>  
> -  /* Make DEST point before next character, so we can increment
> -     it while memory is read (wins on pipelined cpus).	*/
> -  dest -= 2;
> +  size_t ds = __wcsnlen (src, n);
>  
> -  if (n >= 4)
> -    {
> -      size_t n4 = n >> 2;
> -      do
> -	{
> -	  c = *src++;
> -	  *++dest = c;
> -	  if (c == L'\0')
> -	    return s;
> -	  c = *src++;
> -	  *++dest = c;
> -	  if (c == L'\0')
> -	    return s;
> -	  c = *src++;
> -	  *++dest = c;
> -	  if (c == L'\0')
> -	    return s;
> -	  c = *src++;
> -	  *++dest = c;
> -	  if (c == L'\0')
> -	    return s;
> -	} while (--n4 > 0);
> -      n &= 3;
> -    }
> +  dest[ds] = L'\0';
> +  __wmemcpy (dest, src, ds);
>  
> -  while (n > 0)
> -    {
> -      c = *src++;
> -      *++dest = c;
> -      if (c == L'\0')
> -	return s;
> -      n--;
> -    }
> -
> -  if (c != L'\0')
> -    *++dest = L'\0';
> -
> -  return s;
> +  return ret;
>  }
>