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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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