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Message-ID: <20240227140756.216904-1-tirtajames45@gmail.com>
Date: Tue, 27 Feb 2024 21:07:56 +0700
From: James Tirta Halim <tirtajames45@...il.com>
To: musl@...ts.openwall.com
Cc: James Tirta Halim <tirtajames45@...il.com>
Subject: [PATCH] add memcmpeq: memcmp that returns length of first mismatch
(unaligned access must be supported for mempcmpeq if using word access)
mempcmpeq returns the length of the first mismatched byte. If S1 and S2
are equal, n is returned.
The function is meant to be used internally in strstr and memmem:
https://inbox.vuxu.org/musl/20181108193451.GD5150@brightrain.aerifal.cx/
glibc bench-memcmpeq timings (Core i3-1115G4):
mempcmpeq memcmp_musl memcmp __memcmpeq_evex __memcmpeq_avx2 __memcmpeq_sse2
Average:
62.3978 269.813 16.0426 14.9072 14.1125 20.6527
Total:
30637.3 132478 7876.92 7319.43 6929.23 10140.5
Passes glibc test-memcmpeq.
Return value in testing and benchmarking is changed to suit the
behavior of memcmpeq.
---
src/string/mempcmpeq.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
create mode 100644 src/string/mempcmpeq.c
diff --git a/src/string/mempcmpeq.c b/src/string/mempcmpeq.c
new file mode 100644
index 00000000..bc17bc58
--- /dev/null
+++ b/src/string/mempcmpeq.c
@@ -0,0 +1,19 @@
+#include <stddef.h>
+
+size_t
+mempcmpeq(const void *s1,
+ const void *s2,
+ size_t n)
+{
+ const size_t length = n;
+#ifdef __GNUC__
+ typedef size_t __attribute__((__may_alias__)) word;
+ const unsigned char *p1 = (const unsigned char *)s1;
+ const unsigned char *p2 = (const unsigned char *)s2;
+ for (; n >= sizeof(word) && *(word *)p1 == *(word *)p2; p1+=sizeof(word), p2+=sizeof(word), n-=sizeof(word));
+#endif
+ for (; n; --n)
+ if (*p1++ != *p2++)
+ return (size_t)((p1 - 1 - (const unsigned char *)s1));
+ return length;
+}
--
2.44.0
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