Re: [PATCH] xdiff: optimise for no whitespace difference when ignoring whitespace.

From: Michael J Gruber <git@drmicha.warpmail.net>
Date: Jul 5, 2010, 08:34 UTC
Message-ID: <4C319931.4020603@drmicha.warpmail.net>
In-Reply-To: <1278310017-24299-1-git-send-email-dgreid@gmail.com>

Dylan Reid venit, vidit, dixit 05.07.2010 08:06:

> Invert the order of the memcmp and flag check are done in xdl_recmatch,

I was wondering whether you describe old (before patch) or new (after patch) here. Maybe one of the following is clearer:

"Invert the order of the memcmp and flag check which are done in xdl_recmatch,"

"Invert the order of the memcmp and flag check in xdl_recmatch,"

Show 22 quoted lines

> as it makes the common case (there is no whitespace difference) faster.
> It costs the case where lines are the same length and contain
> whitespace differences, but the common case is more than 20% faster.
> 
> Signed-off-by: Dylan Reid <dgreid@gmail.com>
> ---
>  xdiff/xutils.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/xdiff/xutils.c b/xdiff/xutils.c
> index bc12f29..dc97a21 100644
> --- a/xdiff/xutils.c
> +++ b/xdiff/xutils.c
> @@ -190,8 +190,10 @@ int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags)
>  {
>  	int i1, i2;
>  
> -	if (!(flags & XDF_WHITESPACE_FLAGS))
> -		return s1 == s2 && !memcmp(l1, l2, s1);
> +	if (s1 == s2 && !memcmp(l1, l2, s1))
> +		return 1;
> +	else if (!(flags & XDF_WHITESPACE_FLAGS))

You can do without the "else" here.

> +		return 0;
>  
>  	i1 = 0;
>  	i2 = 0;

BTW: How did you find this? Are you profiling parts of git?

Michael