[PATCH 4/4] last_char_is: code shrink

Martin Lewis martin.lewis.x84 at gmail.com
Wed Jul 1 13:34:50 UTC 2020


Notice that there's a "-" before the line with strlen.
Here's the final implementation to simplify reading:

char* FAST_FUNC last_char_is(const char *s, int c)
{
    if (s) {
        char *index = strrchr(s, c);
        if (index && *(index + 1) == '\0')
            return index;
    }
    return NULL;
}

On Tue, 30 Jun 2020 at 10:59, Jody Bruchon <jody at jodybruchon.com> wrote:

> strlen scans the string; strrchr also scans the string.
>
> On 2020-07-01 10:23, Martin Lewis wrote:
> > Hi,
> >
> > I'm not sure what I'm missing, from a quick glance at strrchr
> > (glibc's) it seems that it scans the string only once?
> >
> > Thank you,
> > Martin
> >
> > On Tue, 30 Jun 2020 at 01:34, Denys Vlasenko <vda.linux at googlemail.com
> > <mailto:vda.linux at googlemail.com>> wrote:
> >
> >     This scans the string twice, unnecessarily. Let's not do that.
> >
> >     On Thu, Jun 11, 2020 at 3:45 PM Martin Lewis
> >     <martin.lewis.x84 at gmail.com <mailto:martin.lewis.x84 at gmail.com>>
> >     wrote:
> >     >
> >     > function                                             old    new
> >      delta
> >     > last_char_is                                          53     30
> >        -23
> >     >
> >
>  ------------------------------------------------------------------------------
> >     > (add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-23)      Total:
> >     -23 bytes
> >     >    text    data     bss     dec     hex filename
> >     >  981322   16915    1872 1000109   f42ad busybox_old
> >     >  981299   16915    1872 1000086   f4296 busybox_unstripped
> >     >
> >     > Signed-off-by: Martin Lewis <martin.lewis.x84 at gmail.com
> >     <mailto:martin.lewis.x84 at gmail.com>>
> >     > ---
> >     >  libbb/last_char_is.c | 9 ++++-----
> >     >  1 file changed, 4 insertions(+), 5 deletions(-)
> >     >
> >     > diff --git a/libbb/last_char_is.c b/libbb/last_char_is.c
> >     > index 66f2e3635..1fff08f9f 100644
> >     > --- a/libbb/last_char_is.c
> >     > +++ b/libbb/last_char_is.c
> >     > @@ -13,11 +13,10 @@
> >     >   */
> >     >  char* FAST_FUNC last_char_is(const char *s, int c)
> >     >  {
> >     > -       if (s && *s) {
> >     > -               size_t sz = strlen(s) - 1;
> >     > -               s += sz;
> >     > -               if ( (unsigned char)*s == c)
> >     > -                       return (char*)s;
> >     > +       if (s) {
> >     > +               char *index = strrchr(s, c);
> >     > +               if (index && *(index + 1) == '\0')
> >     > +                       return index;
> >     >         }
> >     >         return NULL;
> >     >  }
> >     > --
> >     > 2.11.0
> >     >
> >     > _______________________________________________
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> >
> >
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