Re: [PATCH] Optimize prefixcmp()

> On Sun, Dec 30, 2007 at 01:02:28PM +0000, Marco Costalba wrote:
> > Subject: [PATCH] Certain codepaths (notably "git log --pretty=format...") use
> > 
> > prefixcmp() extensively, with very short prefixes.  In those cases,
> > calling strlen() is a wasteful operation, so avoid it.
> > 
> > Initial patch by Johannes Schindelin.
> > 
> > Signed-off-by: Marco Costalba <mcostalba@gmail.com>
> > ---
> >  git-compat-util.h |   11 ++++++++++-
> >  1 files changed, 10 insertions(+), 1 deletions(-)
> > 
> > diff --git a/git-compat-util.h b/git-compat-util.h
> > index 79eb10e..843a8f5 100644
> > --- a/git-compat-util.h
> > +++ b/git-compat-util.h
> > @@ -398,7 +398,16 @@ static inline int sane_case(int x, int high)
> > 
> >  static inline int prefixcmp(const char *str, const char *prefix)
> >  {
> > -	return strncmp(str, prefix, strlen(prefix));
> > +	do {
> > +		if (*str != *prefix)
> > +			return *(unsigned const char *)prefix - *(unsigned const char *)str;
> > +
> > +		if (!*(++prefix))
> > +			return 0;
> > +
> > +		str++;
> > +
> > +	} while (1);
> 
>   This code doesn't work if prefix is "". You want something like:
> 
>     for (; *prefix; prefix++, str++) {
>         if (*str != *prefix)
>             return *(unsigned const char *)prefix - *(unsigned const char *)str;
>     }
>     return 0;