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

From: Patrick Steinhardt <[email-masked]>
Date: Mon, 19 May 2025 09:18:00 +0200

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.

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.

Patrick