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authorWilco Dijkstra <wdijkstr@arm.com>2015-08-05 15:15:28 +0100
committerWilco Dijkstra <wdijkstr@arm.com>2015-08-05 16:24:02 +0100
commitf6482cf29d3094ca9688be59802353014c528959 (patch)
tree11e8c2855b92cb90ce2a16ad55151c60e8d6962f
parent7b1c56e4834aa3b139fea39ded64a7e901be89a2 (diff)
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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.
-rw-r--r--ChangeLog5
-rw-r--r--string/strncpy.c59
2 files changed, 10 insertions, 54 deletions
diff --git a/ChangeLog b/ChangeLog
index d013561..5f40e4e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
2015-08-05 Wilco Dijkstra <wdijkstr@arm.com>
+ * string/strncpy.c (strncpy):
+ Improve performance by using __strnlen/memcpy.
+
+2015-08-05 Wilco Dijkstra <wdijkstr@arm.com>
+
* sysdeps/aarch64/fpu/feenablxcpt.c (feenableexcept):
Optimize to avoid an unnecessary FPCR read.
diff --git a/string/strncpy.c b/string/strncpy.c
index 37af5aa..d464bbb 100644
--- a/string/strncpy.c
+++ b/string/strncpy.c
@@ -16,68 +16,19 @@
<http://www.gnu.org/licenses/>. */
#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;
- }
- s1++;
- n = n - (s1 - s);
- memset (s1, '\0', n);
- return s;
- }
-
- last_chars:
- n &= 3;
- if (n == 0)
- return s;
-
- do
- {
- c = *s2++;
- *++s1 = c;
- if (--n == 0)
- return s;
- }
- while (c != '\0');
-
- memset (s1 + 1, '\0', n);
- 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)