This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
RE: [PATCH][PING] Improve stpncpy performance
- From: "Wilco Dijkstra" <wdijkstr at arm dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Mon, 6 Jul 2015 12:29:24 +0100
- Subject: RE: [PATCH][PING] Improve stpncpy performance
- Authentication-results: sourceware.org; auth=none
- References:
> Wilco wrote:
> 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