[PATCH 4/4] last_char_is: code shrink

[Jody Bruchon]

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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