Re: [PATCH 3/3] match_basename: use strncmp instead of strcmp

Nguyễn Thái Ngọc Duy  [off-list ref] writes:

strncmp provides length information, compared to strcmp, which could
be taken advantage by the implementation. Even better, we could check
if the lengths are equal before calling strncmp, eliminating a bit of
strncmp calls.

I think I am a bit slower than my usual self tonight, but I am
utterly confused by the above.

strncmp() compares _only_ up to the first n bytes, so when you are
using it for equality, it is not "we could check length", but is "we
MUST check they match to the length of the shorter string", if you
want to obtain not just faster but correct result.

Am I mistaken?

Even if you are using strcmp() that yields ordering not just
equality, it can return a correct result as soon as it hits the
first bytes that are different; I doubt using strncmp() contributes
to the performance very much.  Comparing lengths before doing
byte-for-byte comparison could help because you can reject two
strings with different lengths without looking at them.

At the same time, I wonder if we can take advantage of the fact that
these call sites only care about equality and not ordering.