[systemd-devel] [PATCH 1/2] Optimize startswith() to macro

[WANG Chao]

On 08/22/13 at 06:35pm, Zbigniew Jędrzejewski-Szmek wrote:
> On Thu, Aug 22, 2013 at 11:03:11PM +0800, WANG Chao wrote:
> > On 08/22/13 at 06:53am, Zbigniew Jędrzejewski-Szmek wrote:
> > > On Thu, Aug 22, 2013 at 03:52:29AM +0200, Kay Sievers wrote:
> > > > On Wed, Aug 21, 2013 at 10:16 PM, Kay Sievers <kay at vrfy.org> wrote:
> > > > > On Wed, Aug 21, 2013 at 8:15 PM, WANG Chao <chaowang at redhat.com> wrote:
> > > > >> Take this optimized code from Lennart[1]. Now startswith is a macro using
> > > > >> strncmp and should be fast enough.
> > > > >>
> > > > >> [1]: http://lists.freedesktop.org/archives/systemd-devel/2013-July/011860.html
> > > > >> ---
> > > > >>  src/shared/macro.h |  5 +++++
> > > > >>  src/shared/util.c  | 17 -----------------
> > > > >>  2 files changed, 5 insertions(+), 17 deletions(-)
> > > > >
> > > > > It fails to compile, there are the prototypes in util.h still.
> > > > > Also quite a few places do not include macro.h ...
> > > > >
> > > > > I guess it's easier and cleaner anyway to use simple static inline
> > > > > functions instead of defines. Patch attached.
> > > > 
> > > > Zbigniew, mind checking if that patch makes sense?
> > > > 
> > > > You added the hasprefix a while ago, and you also proposed a version
> > > > to unify the both.
> > > > We really should get that topic sorted out now. :)
> > > Looks correct, pushed this along with Shawn's patch.
> > > 
> > 
> > Hi, guys, I have two more questions:
> > 
> > - Do we need to update endswith() to be static inline and use strncmp
> >   instead of memcmp. It looks better if we put these two functions at
> >   the same place (shared/util.h)
> Sounds useful.
> 
> > - Why not use startswith() instead of first_word()?
> first_word is not equivalent: there must be a word boundary after the
> word:

Yeah, you're right. I occasionally got carried away at midnight :(

And I think a inline static version could be a little faster? Right?

> 
> src/test/test-util.c:static void test_first_word(void) {
> src/test/test-util.c:        assert_se(first_word("Hello", ""));
> src/test/test-util.c:        assert_se(first_word("Hello", "Hello"));
> src/test/test-util.c:        assert_se(first_word("Hello world", "Hello"));
> src/test/test-util.c:        assert_se(first_word("Hello\tworld", "Hello"));
> src/test/test-util.c:        assert_se(first_word("Hello\nworld", "Hello"));
> src/test/test-util.c:        assert_se(first_word("Hello\rworld", "Hello"));
> src/test/test-util.c:        assert_se(first_word("Hello ", "Hello"));
> src/test/test-util.c:        assert_se(!first_word("Hello", "Hellooo"));
> src/test/test-util.c:        assert_se(!first_word("Hello", "xxxxx"));
> src/test/test-util.c:        assert_se(!first_word("Hellooo", "Hello"));
> 
> Zbyszek
>