Re: [PATCH] interpret_nth_last_branch(): avoid traversing the reflogs twice

From

Johannes Schindelin <johannes.schindelin@gmx.de>

Date

Jan 19, 2009, 12:33 UTC

Message-ID

<alpine.DEB.1.00.0901191331590.3586@pacific.mpi-cbg.de>

In-Reply-To

<7vljt7r9mq.fsf@gitster.siamese.dyndns.org>

Hi,

On Mon, 19 Jan 2009, Junio C Hamano wrote:

> Junio C Hamano <gitster@pobox.com> writes:
> 
> > Well, I would rather be in favor of something like this.
> >
> > -- >8 --
> > Subject: interpret_nth_last_branch(): avoid traversing the reflog twice
> >
> > You can have quite a many reflog entries, but you typically won't recall
> > which branch you were on after switching branches for more than several
> > times.
> >
> > Instead of reading the reflog twice, this reads the branch switching event
> > and keeps the latest 16 (which is an arbitrary limitation that should be
> > plenty) such entry, to switch back to the branch we were recently on.
> >
> > Signed-off-by: Junio C Hamano <gitster@pobox.com>
> > ---
> >  sha1_name.c              |   48 +++++++++++++++++++++------------------------
> >  t/t2012-checkout-last.sh |   44 ++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 66 insertions(+), 26 deletions(-)
> >
> > diff --git a/sha1_name.c b/sha1_name.c
> > index 9e1538e..d6622f2 100644
> > --- a/sha1_name.c
> > +++ b/sha1_name.c
> > @@ -750,19 +746,19 @@ int interpret_nth_last_branch(const char *name, struct strbuf *buf)
> >  	nth = strtol(name+3, &num_end, 10);
> >  	if (num_end != brace)
> >  		return -1;
> > ...
> > -	if (cb.nth < nth)
> > -		return 0;
> > ...
> > +	if (cb.cnt < nth)
> > +		return -1;
> 
> This should (obviously) be "return 0".

-- snipsnap --

diff --git a/sha1_name.c b/sha1_name.c
index 2c5461e..9e5f444 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -691,11 +691,9 @@ static int get_sha1_oneline(const char *prefix, unsigned char *sha1)
 	return retval;
 }
 
-#define MAX_PREVIOUS_BRANCH 16
-
 struct grab_nth_branch_switch_cbdata {
-	long cnt;
-	struct strbuf buf[MAX_PREVIOUS_BRANCH];
+	long cnt, alloc;
+	struct strbuf *buf;
 };
 
 static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
@@ -720,7 +718,7 @@ static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
 	if (target[len] == '\n' && !strncmp(match, target, len))
 		return 0;
 
-	nth = cb->cnt++ % MAX_PREVIOUS_BRANCH;
+	nth = cb->cnt++ % cb->alloc;
 	strbuf_reset(&cb->buf[nth]);
 	strbuf_add(&cb->buf[nth], match, len);
 	return 0;
@@ -753,19 +751,22 @@ int interpret_nth_last_branch(const char *name, struct strbuf *buf)
 	nth = strtol(name+3, &num_end, 10);
 	if (num_end != brace)
 		return -1;
-	if (nth <= 0 || MAX_PREVIOUS_BRANCH < nth)
+	if (nth <= 0)
 		return -1;
-	for (i = 0; i < MAX_PREVIOUS_BRANCH; i++)
+	cb.alloc = nth;
+	cb.buf = xmalloc(nth * sizeof(struct strbuf));
+	for (i = 0; i < nth; i++)
 		strbuf_init(&cb.buf[i], 20);
 	cb.cnt = 0;
 	for_each_reflog_ent("HEAD", grab_nth_branch_switch, &cb);
 	if (cb.cnt < nth)
-		return -1;
-	i = (cb.cnt + MAX_PREVIOUS_BRANCH - nth) % MAX_PREVIOUS_BRANCH;
+		return 0;
+	i = cb.cnt % nth;
 	strbuf_reset(buf);
 	strbuf_add(buf, cb.buf[i].buf, cb.buf[i].len);
-	for (i = 0; i < MAX_PREVIOUS_BRANCH; i++)
+	for (i = 0; i < nth; i++)
 		strbuf_release(&cb.buf[i]);
+	free(cb.buf);
 
 	return brace-name+1;
 }

-- 
1.6.1.347.g7b62749