string-list: replace negative index encoding with "exact_match" parameter

The "string_list_find_insert_index()" function is used to determine
the correct insertion index for a new string within the string list.
The function also doubles up to convey if the string is already
existing in the list, this is done by returning a negative index
"-1 -index". Users are expected to decode this information. This
approach has several limitations:

1. It requires the callers to look into the detail of the function to
   understand how to decode the negative index encoding.
2. Using int for indices can cause overflow issues when dealing with
   large string lists.

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 <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: shejialuo

add-interactive.c

@@ -221,16 +221,17 @@ 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)
 		BUG("prefix_item_list in inconsistent state (%"PRIuMAX
 		    " 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;

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];
 		/*

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;
 

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)

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