path: root/src/string/memmem.c
diff options
authorRich Felker <>2018-11-08 15:00:02 -0500
committerRich Felker <>2018-11-08 15:22:22 -0500
commit122d67f846cb0be2c9e1c3880db9eb9545bbe38c (patch)
treea219e7810b20690c12a6ab14e47f9c57b03ac7b9 /src/string/memmem.c
parent04e18b61dfde85e34ddea15e4a7d49f24c47bb73 (diff)
optimize two-way strstr and memmem bad character shift
first, the condition (mem && k < p) is redundant, because mem being nonzero implies the needle is periodic with period exactly p, in which case any byte that appears in the needle must appear in the last p bytes of the needle, bounding the shift (k) by p. second, the whole point of replacing the shift k by mem (=l-p) is to prevent shifting by less than mem when discarding the memory on shift, in which case linear time could not be guaranteed. but as written, the check also replaced shifts greater than mem by mem, reducing the benefit of the shift. there is no possible benefit to this reduction of the shift; since mem is being cleared, the full shift is valid and more optimal. so only replace the shift by mem when it would be less than mem.
Diffstat (limited to 'src/string/memmem.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/src/string/memmem.c b/src/string/memmem.c
index ce3cd190..58a21fcd 100644
--- a/src/string/memmem.c
+++ b/src/string/memmem.c
@@ -100,7 +100,7 @@ static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const
if (BITOP(byteset, h[l-1], &)) {
k = l-shift[h[l-1]];
if (k) {
- if (mem && k < p) k = l-p;
+ if (k < mem) k = mem;
h += k;
mem = 0;