* Jonathan Nieder <jrnieder@xxxxxxxxx> wrote:
> Hi,
>
> A side note for amusement.
>
> Erik Faye-Lund wrote:
>
> > --- a/cache.h
> > +++ b/cache.h
> > @@ -681,13 +681,17 @@ extern char *sha1_pack_name(const unsigned char *sha1);
> > extern char *sha1_pack_index_name(const unsigned char *sha1);
> > extern const char *find_unique_abbrev(const unsigned char *sha1, int);
> > extern const unsigned char null_sha1[20];
> > -static inline int is_null_sha1(const unsigned char *sha1)
> > +static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
> > {
> > - return !memcmp(sha1, null_sha1, 20);
> > + /* early out for fast mis-match */
> > + if (*sha1 != *sha2)
> > + return *sha1 - *sha2;
> > +
> > + return memcmp(sha1 + 1, sha2 + 1, 19);
> > }
>
> On the off-chance that sha1 and sha2 are nicely aligned, a more
> redundant
>
> if (*sha1 != *sha2)
> return *sha1 - *sha2;
>
> return memcmp(sha1, sha2, 20);
>
> would take advantage of that (yes, this is just superstition, but it
> somehow seems comforting anyway).
Your variant also makes the code slightly more compact as the sha1+1 and sha2+1
addresses do not have to be computed. I'll re-test and resend this variant.
Thanks,
Ingo
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