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RE: [PATCH] Improve stpncpy performance
- From: "Wilco Dijkstra" <wdijkstr at arm dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Wed, 15 Apr 2015 13:32:22 +0100
- Subject: RE: [PATCH] Improve stpncpy performance
- Authentication-results: sourceware.org; auth=none
- References:
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