Subject: Re: [PATCH v2 3/8] string-list: return index directly when inserting an existing element

From: shejialuo <[email-masked]>
Date: Mon, 26 May 2025 22:13:02 +0800

On Mon, May 19, 2025 at 09:18:00AM +0200, Patrick Steinhardt wrote:
> On Sun, May 18, 2025 at 11:57:15PM +0800, shejialuo wrote:
> > When inserting an existing element, "add_entry" would convert "index"
> > value to "-1-index" to indicate the caller that this element is in the
> > list already.
> > 
> > However, in "string_list_insert", we would simply convert this to the
> > original positive index without any further action. Let's directly
> > return the index as we don't care about whether the element is in the
> > list by using "add_entry".
> > 
> > In the future, if we want to let "add_entry" tell the caller, we may add
> > "int *exact_match" parameter to "add_entry" instead of converting the
> > index to negative to indicate.
> > 
> > Signed-off-by: shejialuo <[email-masked]>
> > ---
> >  string-list.c | 6 +-----
> >  1 file changed, 1 insertion(+), 5 deletions(-)
> > 
> > diff --git a/string-list.c b/string-list.c
> > index 8540c29bc9..171cef5dbb 100644
> > --- a/string-list.c
> > +++ b/string-list.c
> > @@ -40,14 +40,13 @@ static int get_entry_index(const struct string_list *list, const char *string,
> >  	return right;
> >  }
> >  
> > -/* returns -1-index if already exists */
> >  static int add_entry(struct string_list *list, const char *string)
> >  {
> >  	int exact_match = 0;
> >  	int index = get_entry_index(list, string, &exact_match);
> >  
> >  	if (exact_match)
> > -		return -1 - index;
> > +		return index;
> >  
> >  	ALLOC_GROW(list->items, list->nr+1, list->alloc);
> >  	if (index < list->nr)
> 
> Okay, let's assume that "index == 2" here and we have an exact match.
> We'd thus return `-1 - 2 == -3`.
> 
> > @@ -65,9 +64,6 @@ struct string_list_item *string_list_insert(struct string_list *list, const char
> >  {
> >  	int index = add_entry(list, string);
> >  
> > -	if (index < 0)
> > -		index = -1 - index;
> > -
> >  	return list->items + index;
> >  }
> 
> So we'd now realize that `index < 0` and thus calculate `-1 - -3 == 2`,
> which is the original index indeed. So this is a nice simplification
> that retains the original behaviour indeed.
> 

That's right. Actually, when I find out this by simply calculating `(-1
- (-1 - index)) == index`, I am a little surprised.

> I think we could simplify the code even further by inlining
> `get_entry_index()` now that `string_list_insert()` is a trivial wrapper
> around it. But I'll leave it up to you whether we want to do it or not.
> 

That's right. But as code it is, let's just keep this which won't hurt
too much.

Thanks,
Jialuo