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authorWilco Dijkstra <wdijkstr@arm.com>2019-04-09 11:46:28 +0100
committerWilco Dijkstra <wdijkstr@arm.com>2019-04-09 11:46:28 +0100
commita173d09f85a1f7e74e8b7ae7da04743a77cc7552 (patch)
treea62c6b098a743f9d44a39168dbc35d145be6934b /benchtests
parent6103c0a8116960527708e8fc030a6c043cf51bb5 (diff)
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Improve bench-memmem
Improve bench-memmem by replacing simple_memmem with a more efficient implementation. Add the Two-way implementation to enable direct comparison with the optimized memmem. * benchtests/bench-memmem.c (simple_memmem): Remove function. (basic_memmem): Add function. (twoway_memmem): Add function.
Diffstat (limited to 'benchtests')
-rw-r--r--benchtests/bench-memmem.c79
1 files changed, 62 insertions, 17 deletions
diff --git a/benchtests/bench-memmem.c b/benchtests/bench-memmem.c
index 4936b23..b6b97f3 100644
--- a/benchtests/bench-memmem.c
+++ b/benchtests/bench-memmem.c
@@ -19,22 +19,51 @@
#define TEST_MAIN
#define TEST_NAME "memmem"
#define BUF1PAGES 20
-#define ITERATIONS 500
+#define ITERATIONS 100
#include "bench-string.h"
typedef char *(*proto_t) (const void *, size_t, const void *, size_t);
-void *simple_memmem (const void *, size_t, const void *, size_t);
-IMPL (simple_memmem, 0)
-IMPL (memmem, 1)
+void *
+basic_memmem (const void *haystack, size_t hs_len, const void *needle,
+ size_t ne_len)
+{
+ const char *hs = haystack;
+ const char *ne = needle;
+
+ if (ne_len == 0)
+ return (void *)hs;
+ int i;
+ int c = ne[0];
+ const char *end = hs + hs_len - ne_len;
+
+ for ( ; hs <= end; hs++)
+ {
+ if (hs[0] != c)
+ continue;
+ for (i = ne_len - 1; i != 0; i--)
+ if (hs[i] != ne[i])
+ break;
+ if (i == 0)
+ return (void *)hs;
+ }
+
+ return NULL;
+}
+
+#define RETURN_TYPE void *
+#define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))
+#define FASTSEARCH(S,C,N) (void*) memchr ((void *)(S), (C), (N))
+#include "../string/str-two-way.h"
void *
-simple_memmem (const void *haystack, size_t haystack_len, const void *needle,
- size_t needle_len)
+twoway_memmem (const void *haystack_start, size_t haystack_len,
+ const void *needle_start, size_t needle_len)
{
- const char *begin;
- const char *const last_possible
- = (const char *) haystack + haystack_len - needle_len;
+ /* Abstract memory is considered to be an array of 'unsigned char' values,
+ not an array of 'char' values. See ISO C 99 section 6.2.6.1. */
+ const unsigned char *haystack = (const unsigned char *) haystack_start;
+ const unsigned char *needle = (const unsigned char *) needle_start;
if (needle_len == 0)
/* The first occurrence of the empty string is deemed to occur at
@@ -46,16 +75,32 @@ simple_memmem (const void *haystack, size_t haystack_len, const void *needle,
if (__glibc_unlikely (haystack_len < needle_len))
return NULL;
- for (begin = (const char *) haystack; begin <= last_possible; ++begin)
- if (begin[0] == ((const char *) needle)[0]
- && !memcmp ((const void *) &begin[1],
- (const void *) ((const char *) needle + 1),
- needle_len - 1))
- return (void *) begin;
-
- return NULL;
+ /* Use optimizations in memchr when possible, to reduce the search
+ size of haystack using a linear algorithm with a smaller
+ coefficient. However, avoid memchr for long needles, since we
+ can often achieve sublinear performance. */
+ if (needle_len < LONG_NEEDLE_THRESHOLD)
+ {
+ haystack = memchr (haystack, *needle, haystack_len);
+ if (!haystack || __builtin_expect (needle_len == 1, 0))
+ return (void *) haystack;
+ haystack_len -= haystack - (const unsigned char *) haystack_start;
+ if (haystack_len < needle_len)
+ return NULL;
+ /* Check whether we have a match. This improves performance since we
+ avoid the initialization overhead of the two-way algorithm. */
+ if (memcmp (haystack, needle, needle_len) == 0)
+ return (void *) haystack;
+ return two_way_short_needle (haystack, haystack_len, needle, needle_len);
+ }
+ else
+ return two_way_long_needle (haystack, haystack_len, needle, needle_len);
}
+IMPL (memmem, 1)
+IMPL (twoway_memmem, 0)
+IMPL (basic_memmem, 0)
+
static void
do_one_test (impl_t *impl, const void *haystack, size_t haystack_len,
const void *needle, size_t needle_len, const void *expected)