From: David Kastrup <dak@gnu.org>
Date: Sun, 07 Oct 2007 14:24:57 GMT
Subject: Re: [PATCH] Make strbuf_cmp inline, constify its arguments and optimize it a bit
Message-ID: <85fy0nknnq.fsf@lola.goethe.zz>
In-Reply-To: <20071007140052.GA3260@steel.home>

Alex Riesen <raa.lkml@gmail.com> writes:

> It is definitely less code (also object code). It is not always
> measurably faster (but mostly is).

> -int strbuf_cmp(struct strbuf *a, struct strbuf *b)
> -{
> -	int cmp;
> -	if (a->len < b->len) {
> -		cmp = memcmp(a->buf, b->buf, a->len);
> -		return cmp ? cmp : -1;
> -	} else {
> -		cmp = memcmp(a->buf, b->buf, b->len);
> -		return cmp ? cmp : a->len != b->len;
> -	}
> -}
> -

> +static inline int strbuf_cmp(const struct strbuf *a, const struct strbuf *b)
> +{
> +	int len = a->len < b->len ? a->len: b->len;
> +	int cmp = memcmp(a->buf, b->buf, len);
> +	if (cmp)
> +		return cmp;
> +	return a->len < b->len ? -1: a->len != b->len;
> +}

My guess is that you are conflating two issues about speed here: the
inlining will like speed the stuff up.  But having to evaluate the
(a->len < b->len) comparison twice will likely slow it down.

So if you do any profiling, you should do it on both separate angles
of this patch.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum