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RE: [PATCH] Improve stpncpy performance


ping

> -----Original Message-----
> From: Wilco Dijkstra [mailto:wdijkstr@arm.com]
> Sent: 12 January 2015 15:09
> To: 'libc-alpha@sourceware.org'
> Subject: [PATCH] Improve stpncpy performance
> 
> Like strncpy, this patch improves stpncpy performance by using strnlen/memcpy/memset rather
> than a byte loop. Performance on bench-stpncpy is ~2x faster on average.
> 
> ChangeLog:
> 
> 2015-01-12 Wilco Dijkstra wdijkstr@arm.com
> 
> 	* string/stpncpy.c (stpncpy): Improve performance using
> 	__strnlen/memcpy/memset.
> 
> ---
>  string/stpncpy.c | 59 ++++++--------------------------------------------------
>  1 file changed, 6 insertions(+), 53 deletions(-)
> 
> diff --git a/string/stpncpy.c b/string/stpncpy.c
> index fad747e..50521aa 100644
> --- a/string/stpncpy.c
> +++ b/string/stpncpy.c
> @@ -15,7 +15,7 @@
>     License along with the GNU C Library; if not, see
>     <http://www.gnu.org/licenses/>.  */
> 
> -/* This is almost copied from strncpy.c, written by Torbjorn Granlund.  */
> +#include <stddef.h>
> 
>  #ifdef HAVE_CONFIG_H
>  # include <config.h>
> @@ -41,59 +41,12 @@ weak_alias (__stpncpy, stpncpy)
>  char *
>  STPNCPY (char *dest, const char *src, size_t n)
>  {
> -  char c;
> -  char *s = dest;
> -
> -  if (n >= 4)
> -    {
> -      size_t n4 = n >> 2;
> -
> -      for (;;)
> -	{
> -	  c = *src++;
> -	  *dest++ = c;
> -	  if (c == '\0')
> -	    break;
> -	  c = *src++;
> -	  *dest++ = c;
> -	  if (c == '\0')
> -	    break;
> -	  c = *src++;
> -	  *dest++ = c;
> -	  if (c == '\0')
> -	    break;
> -	  c = *src++;
> -	  *dest++ = c;
> -	  if (c == '\0')
> -	    break;
> -	  if (--n4 == 0)
> -	    goto last_chars;
> -	}
> -      n -= dest - s;
> -      goto zero_fill;
> -    }
> -
> - last_chars:
> -  n &= 3;
> -  if (n == 0)
> +  size_t size = __strnlen (src, n);
> +  memcpy (dest, src, size);
> +  dest += size;
> +  if (size == n)
>      return dest;
> -
> -  for (;;)
> -    {
> -      c = *src++;
> -      --n;
> -      *dest++ = c;
> -      if (c == '\0')
> -	break;
> -      if (n == 0)
> -	return dest;
> -    }
> -
> - zero_fill:
> -  while (n-- > 0)
> -    dest[n] = '\0';
> -
> -  return dest - 1;
> +  return memset (dest, '\0', n - size);
>  }
>  #ifdef weak_alias
>  libc_hidden_def (__stpncpy)
> --
> 1.9.1





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