Re: [PATCH 1/4] strncmp: Add a testcase for page boundary [BZ #25933]

["H.J. Lu" <hjl.tools@gmail.com>]

On Mon, Jun 15, 2020 at 1:29 PM Paul A. Clarke <pc@us.ibm.com> wrote:
>
> On Fri, Jun 12, 2020 at 01:10:53PM -0700, H.J. Lu via Libc-alpha wrote:
> > Add a strncmp testcase to cover cases where one of strings ends on the
> > page boundary.
> > ---
> >  string/test-strncmp.c | 25 +++++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> >
> > diff --git a/string/test-strncmp.c b/string/test-strncmp.c
> > index d961ac4493..d0928a2864 100644
> > --- a/string/test-strncmp.c
> > +++ b/string/test-strncmp.c
> > @@ -403,6 +403,30 @@ check2 (void)
> >    free (s2);
> >  }
> >
> > +static void
> > +check3 (void)
> > +{
> > +  size_t size = 32 * 4;
> > +  CHAR *s1 = (CHAR *) (buf1 + (BUF1PAGES - 1) * page_size);
> > +  CHAR *s2 = (CHAR *) (buf2 + (BUF1PAGES - 1) * page_size);
> > +  int exp_result;
> > +
> > +  memset (s1, 'a', page_size);
> > +  memset (s2, 'a', page_size);
> > +  s1[(page_size / CHARBYTES) - 1] = (CHAR) 0;
> > +
> > +  for (size_t s = 99; s <= size; s++)
> > +    for (size_t s1a = 31; s1a < 32; s1a++)
> > +      for (size_t s2a = 30; s2a < 32; s2a++)
> > +     {
> > +       CHAR *s1p = s1 + (page_size / CHARBYTES - s) - s1a;
> > +       CHAR *s2p = s2 + (page_size / CHARBYTES - s) - s2a;
> > +       exp_result = SIMPLE_STRNCMP (s1p, s2p, s);
> > +       FOR_EACH_IMPL (impl, 0)
> > +         check_result (impl, s1p, s2p, s, exp_result);
> > +     }
> > +}
>
> There are lots of magic numbers here.
>
> Could you add some context around those number

My commit log says

---
Add a strncmp testcase to cover cases where one of strings ends on the
page boundary.
---

> If they are meant to reflect a cache line length, then it's

No.  My testcase is for correctness, not for performance.

> appropriate to support different cache line sizes.
> Rafael Zinsly just did this with strncasecmp in the
> last week or so.
>
> > +
> >  int
> >  test_main (void)
> >  {
> > @@ -412,6 +436,7 @@ test_main (void)
> >
> >    check1 ();
> >    check2 ();
> > +  check3 ();
> >
> >    printf ("%23s", "");
> >    FOR_EACH_IMPL (impl, 0)
> > --
> > 2.26.2
> >



-- 
H.J.