Re: [PATCH 2/3] tree-walk: simplify via strnncmp()

From: Jeremiah Mahler <jmmahler@gmail.com>
Date: Jun 17, 2014, 07:13 UTC
Message-ID: <20140617071332.GA3940@hudson.localdomain>
In-Reply-To: <20140616201806.GO8557@google.com>

Jonathan,

On Mon, Jun 16, 2014 at 01:18:06PM -0700, Jonathan Nieder wrote:

Show 15 quoted lines

> Jeremiah Mahler wrote:
> 
> > --- a/tree-walk.c
> > +++ b/tree-walk.c
> [...]
> > @@ -174,7 +164,7 @@ static int check_entry_match(const char *a, int a_len, const char *b, int b_len)
> >  	 * scanning further.
> >  	 */
> >  
> > -	int cmp = name_compare(a, a_len, b, b_len);
> > +	int cmp = strnncmp(a, a_len, b, b_len);
> 
> This changes behavior: the old version would only have 0 < cmp if
> 'a' comes after 'b', while the new version always has 0 < cmp when
> a != b.

Thanks for catching this. I did not realize that when I tried to cleanup the logic I inadvertently changed its behavior.

    int strnncmp(const char *a, int len_a, const char *b, int len_b)
    {
           int min_len = (len_a < len_b) ? len_a : len_b;
           return (memcmp(a, b, min_len) || (len_a - len_b));
    }

is not the same as:

    static int name_compare(const char *a, int a_len,
                           const char *b, int b_len)
    {
           int len = (a_len < b_len) ? a_len : b_len;
           int cmp = memcmp(a, b, len);
           if (cmp)
                   return cmp;
           return (a_len - b_len);
    }

(-5 || 3) is 1, not -5.

-- 
Jeremiah Mahler
jmmahler@gmail.com
http://github.com/jmahler