Subject: [PATCH v2 2/4] string-list: replace negative index encoding with "exact_match" parameter

From: shejialuo <[email-masked]>
Date: Wed, 17 Sep 2025 17:19:54 +0800

We would return negative index to indicate exact match by converting the
original positive index to be "-1 - index" in
"string_list_find_insert_index", which requires callers to decode this
information. This approach has several limitations:

1. It prevents us from using the full range of size_t, which is
   necessary for large string list.
2. Using int for indices while other parts of the codebase use size_t
   creates signed comparison warnings when these values are compared.

To address these limitations, change the function to return size_t for
the index value and use a separate bool parameter to indicate whether
the index refers to an existing entry or an insertion point.

In some cases, the callers of "string_list_find_insert_index" only need
the index position and don't care whether an exact match is found.
However, "get_entry_index" currently requires a non-NULL "exact_match"
parameter, forcing these callers to declare unnecessary variables.
Let's allow callers to pass NULL for the "exact_match" parameter when
they don't need this information, reducing unnecessary variable
declarations in calling code.

Signed-off-by: shejialuo <[email-masked]>
---
 add-interactive.c |  7 ++++---
 mailmap.c         |  7 +++----
 refs.c            |  2 +-
 string-list.c     | 14 ++++++--------
 string-list.h     |  2 +-
 5 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/add-interactive.c b/add-interactive.c
index 3e692b47ec..7c0fd3d218 100644
--- a/add-interactive.c
+++ b/add-interactive.c
@@ -221,7 +221,8 @@ static void find_unique_prefixes(struct prefix_item_list *list)
 
 static ssize_t find_unique(const char *string, struct prefix_item_list *list)
 {
-	int index = string_list_find_insert_index(&list->sorted, string, 1);
+	bool exact_match;
+	int index = string_list_find_insert_index(&list->sorted, string, &exact_match);
 	struct string_list_item *item;
 
 	if (list->items.nr != list->sorted.nr)
@@ -229,8 +230,8 @@ static ssize_t find_unique(const char *string, struct prefix_item_list *list)
 		    " vs %"PRIuMAX")",
 		    (uintmax_t)list->items.nr, (uintmax_t)list->sorted.nr);
 
-	if (index < 0)
-		item = list->sorted.items[-1 - index].util;
+	if (exact_match)
+		item = list->sorted.items[index].util;
 	else if (index > 0 &&
 		 starts_with(list->sorted.items[index - 1].string, string))
 		return -1;
diff --git a/mailmap.c b/mailmap.c
index 56c72102d9..58a4484963 100644
--- a/mailmap.c
+++ b/mailmap.c
@@ -243,10 +243,9 @@ void clear_mailmap(struct string_list *map)
 static struct string_list_item *lookup_prefix(struct string_list *map,
 					      const char *string, size_t len)
 {
-	int i = string_list_find_insert_index(map, string, 1);
-	if (i < 0) {
-		/* exact match */
-		i = -1 - i;
+	bool exact_match;
+	int i = string_list_find_insert_index(map, string, &exact_match);
+	if (exact_match) {
 		if (!string[len])
 			return &map->items[i];
 		/*
diff --git a/refs.c b/refs.c
index 4ff55cf24f..f1ff5bf846 100644
--- a/refs.c
+++ b/refs.c
@@ -1699,7 +1699,7 @@ const char *find_descendant_ref(const char *dirname,
 	 * with dirname (remember, dirname includes the trailing
 	 * slash) and is not in skip, then we have a conflict.
 	 */
-	for (pos = string_list_find_insert_index(extras, dirname, 0);
+	for (pos = string_list_find_insert_index(extras, dirname, NULL);
 	     pos < extras->nr; pos++) {
 		const char *extra_refname = extras->items[pos].string;
 
diff --git a/string-list.c b/string-list.c
index d8da3dd414..c589ab5a2c 100644
--- a/string-list.c
+++ b/string-list.c
@@ -29,12 +29,14 @@ static size_t get_entry_index(const struct string_list *list, const char *string
 		else if (compare > 0)
 			left = middle + 1;
 		else {
-			*exact_match = true;
+			if (exact_match)
+				*exact_match = true;
 			return middle;
 		}
 	}
 
-	*exact_match = false;
+	if (exact_match)
+		*exact_match = false;
 	return right;
 }
 
@@ -90,13 +92,9 @@ bool string_list_has_string(const struct string_list *list, const char *string)
 }
 
 int string_list_find_insert_index(const struct string_list *list, const char *string,
-				  int negative_existing_index)
+				  bool *exact_match)
 {
-	bool exact_match;
-	int index = get_entry_index(list, string, &exact_match);
-	if (exact_match)
-		index = -1 - (negative_existing_index ? index : 0);
-	return index;
+	return get_entry_index(list, string, exact_match);
 }
 
 struct string_list_item *string_list_lookup(struct string_list *list, const char *string)
diff --git a/string-list.h b/string-list.h
index bc7f38022e..8830ce671d 100644
--- a/string-list.h
+++ b/string-list.h
@@ -174,7 +174,7 @@ void string_list_remove_empty_items(struct string_list *list, int free_util);
 /** Determine if the string_list has a given string or not. */
 bool string_list_has_string(const struct string_list *list, const char *string);
 int string_list_find_insert_index(const struct string_list *list, const char *string,
-				  int negative_existing_index);
+				  bool *exact_match);
 
 /**
  * Insert a new element to the string_list. The returned pointer can
-- 
2.51.0