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Improve strstr performance

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Improve strstr performance.  Strstr tends to be slow because it uses
many calls to memchr and a slow byte loop to scan for the next match.
Performance is significantly improved by using strnlen on larger blocks
and using strchr to search for the next matching character.  strcasestr
can also use strnlen to scan ahead, and memmem can use memchr to check
for the next match.

On the GLIBC bench tests the performance gains on Cortex-A72 are:
strstr: +25%
strcasestr: +4.3%
memmem: +18%

On a 256KB dataset strstr performance improves by 67%, strcasestr by 47%.

    Reviewd-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This commit is contained in:
Wilco Dijkstra
2018-07-16 17:50:09 +01:00
parent 31e422ca96
commit 3ae725dfb6
9 changed files with 50 additions and 33 deletions
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5
string/strstr.c
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@ -33,10 +33,11 @@
#define RETURN_TYPE char *
#define AVAILABLE(h, h_l, j, n_l) \
(!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \
&& ((h_l) = (j) + (n_l)))
(((j) + (n_l) <= (h_l)) || ((h_l) += __strnlen ((void*)((h) + (h_l)), 512), \
(j) + (n_l) <= (h_l)))
#define CHECK_EOL (1)
#define RET0_IF_0(a) if (!a) goto ret0
#define FASTSEARCH(S,C,N) (void*) strchr ((void*)(S), (C))
#include "str-two-way.h"
#undef strstr