[PATCH v3 4/8] string-list: enable sign compare warnings check

From: shejialuo <shejialuo@gmail.com>
Date: Jun 29, 2025, 04:28 UTC
Message-ID: <aGDA1lr_-CXbq75G@ArchLinux>
In-Reply-To: <aGDAZ6a0-PyXXGmK@ArchLinux>

In "add_entry", we call "get_entry_index" function to get the inserted position. However, as the return type of "get_entry_index" function is `int`, there is a sign compare warning when comparing the `index` with the `list-nr` of unsigned type.

"get_entry_index" would always return unsigned index. However, the current binary search algorithm initializes "left" to be "-1", which necessitates the use of signed `int` return type.

The reason why we need to assign "left" to be "-1" is that in the `while` loop, we increment "left" by 1 to determine whether the loop should end. This design choice, while functional, forces us to use signed arithmetic throughout the function.

To resolve this sign comparison issue, let's modify the binary search algorithm with the following approach:

1. Initialize "left" to 0 instead of -1
2. Use `left < right` as the loop termination condition instead of
   `left + 1 < right`
3. When searching the right part, set `left = middle + 1` instead of
   `middle`

Then, we could delete "#define DISABLE_SIGN_COMPARE_WARNING" to enable sign warnings check for "string-list".

Signed-off-by: shejialuo <shejialuo@gmail.com>
---
 string-list.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/string-list.c b/string-list.c
index 171cef5dbb..53faaa8420 100644
--- a/string-list.c
+++ b/string-list.c
@@ -1,5 +1,3 @@
-#define DISABLE_SIGN_COMPARE_WARNINGS
-
 #include "git-compat-util.h"
 #include "string-list.h"
 
@@ -17,19 +15,19 @@ void string_list_init_dup(struct string_list *list)
 
 /* if there is no exact match, point to the index where the entry could be
  * inserted */
-static int get_entry_index(const struct string_list *list, const char *string,
-		int *exact_match)
+static size_t get_entry_index(const struct string_list *list, const char *string,
+			      int *exact_match)
 {
-	int left = -1, right = list->nr;
+	size_t left = 0, right = list->nr;
 	compare_strings_fn cmp = list->cmp ? list->cmp : strcmp;
 
-	while (left + 1 < right) {
-		int middle = left + (right - left) / 2;
+	while (left < right) {
+		size_t middle = left + (right - left) / 2;
 		int compare = cmp(string, list->items[middle].string);
 		if (compare < 0)
 			right = middle;
 		else if (compare > 0)
-			left = middle;
+			left = middle + 1;
 		else {
 			*exact_match = 1;
 			return middle;
@@ -40,10 +38,10 @@ static int get_entry_index(const struct string_list *list, const char *string,
 	return right;
 }
 
-static int add_entry(struct string_list *list, const char *string)
+static size_t add_entry(struct string_list *list, const char *string)
 {
 	int exact_match = 0;
-	int index = get_entry_index(list, string, &exact_match);
+	size_t index = get_entry_index(list, string, &exact_match);
 
 	if (exact_match)
 		return index;
@@ -62,7 +60,7 @@ static int add_entry(struct string_list *list, const char *string)
 
 struct string_list_item *string_list_insert(struct string_list *list, const char *string)
 {
-	int index = add_entry(list, string);
+	size_t index = add_entry(list, string);
 
 	return list->items + index;
 }

-- 
2.50.0