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[PATCH] Improve strncpy performance further
- From: "Wilco Dijkstra" <wdijkstr at arm dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Thu, 8 Jan 2015 18:39:24 -0000
- Subject: [PATCH] Improve strncpy performance further
- Authentication-results: sourceware.org; auth=none
This patch improves strncpy performance by using strnlen/memcpy rather than a byte loop. Performance
on bench-strncpy is 1.9-2.1x faster on average. I tried several variations, and using a tailcall and
calling memset conditionally gave the best overall results.
I'm planning to post a similar patch for stpncpy as well.
ChangeLog:
2015-01-08 Wilco Dijkstra wdijkstr@arm.com
* string/strncpy.c (strncpy): Improve performance using strnlen/memcpy.
---
string/strncpy.c | 64 ++++++--------------------------------------------------
1 file changed, 6 insertions(+), 58 deletions(-)
diff --git a/string/strncpy.c b/string/strncpy.c
index 0915e03..9c516d6 100644
--- a/string/strncpy.c
+++ b/string/strncpy.c
@@ -15,73 +15,21 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
+#include <stddef.h>
#include <string.h>
-#include <memcopy.h>
#undef strncpy
#ifndef STRNCPY
-#define STRNCPY strncpy
+# define STRNCPY strncpy
#endif
char *
STRNCPY (char *s1, const char *s2, size_t n)
{
- char c;
- char *s = s1;
-
- --s1;
-
- if (n >= 4)
- {
- size_t n4 = n >> 2;
-
- for (;;)
- {
- c = *s2++;
- *++s1 = c;
- if (c == '\0')
- break;
- c = *s2++;
- *++s1 = c;
- if (c == '\0')
- break;
- c = *s2++;
- *++s1 = c;
- if (c == '\0')
- break;
- c = *s2++;
- *++s1 = c;
- if (c == '\0')
- break;
- if (--n4 == 0)
- goto last_chars;
- }
- n = n - (s1 - s) - 1;
- if (n == 0)
- return s;
- goto zero_fill;
- }
-
- last_chars:
- n &= 3;
- if (n == 0)
- return s;
-
- do
- {
- c = *s2++;
- *++s1 = c;
- if (--n == 0)
- return s;
- }
- while (c != '\0');
-
- zero_fill:
- do
- *++s1 = '\0';
- while (--n > 0);
-
- return s;
+ size_t size = strnlen (s2, n);
+ if (size != n)
+ memset (s1 + size, '\0', n - size);
+ return memcpy (s1, s2, size);
}
libc_hidden_builtin_def (strncpy)
--
1.9.1