reftable/basics: adjust common_prefix_size() to return size_t

The `common_prefix_size()` function computes the length of the common
prefix between two buffers. As such its return value will always be an
unsigned integer, as the length cannot be negative. Regardless of that,
the function returns a signed integer, which is nonsensical and causes a
couple of -Wsign-compare warnings all over the place.

Adjust the function to return a `size_t` instead.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

reftable/basics.c

@@ -263,14 +263,12 @@ int names_equal(const char **a, const char **b)
 	return a[i] == b[i];
 }
 
-int common_prefix_size(struct reftable_buf *a, struct reftable_buf *b)
+size_t common_prefix_size(struct reftable_buf *a, struct reftable_buf *b)
 {
-	int p = 0;
-	for (; p < a->len && p < b->len; p++) {
+	size_t p = 0;
+	for (; p < a->len && p < b->len; p++)
 		if (a->buf[p] != b->buf[p])
 			break;
-	}
-
 	return p;
 }
 

reftable/basics.h

@@ -169,7 +169,7 @@ static inline void *reftable_alloc_grow(void *p, size_t nelem, size_t elsize,
 #endif
 
 /* Find the longest shared prefix size of `a` and `b` */
-int common_prefix_size(struct reftable_buf *a, struct reftable_buf *b);
+size_t common_prefix_size(struct reftable_buf *a, struct reftable_buf *b);
 
 int hash_size(enum reftable_hash id);
 

reftable/record.c

@@ -144,9 +144,9 @@ int reftable_encode_key(int *restart, struct string_view dest,
 			uint8_t extra)
 {
 	struct string_view start = dest;
-	int prefix_len = common_prefix_size(&prev_key, &key);
+	size_t prefix_len = common_prefix_size(&prev_key, &key);
 	uint64_t suffix_len = key.len - prefix_len;
-	int n = put_var_int(&dest, (uint64_t)prefix_len);
+	int n = put_var_int(&dest, prefix_len);
 	if (n < 0)
 		return -1;
 	string_view_consume(&dest, n);

reftable/writer.c

@@ -577,18 +577,17 @@ static int writer_finish_section(struct reftable_writer *w)
 
 struct common_prefix_arg {
 	struct reftable_buf *last;
-	int max;
+	size_t max;
 };
 
 static void update_common(void *void_arg, void *key)
 {
 	struct common_prefix_arg *arg = void_arg;
 	struct obj_index_tree_node *entry = key;
 	if (arg->last) {
-		int n = common_prefix_size(&entry->hash, arg->last);
-		if (n > arg->max) {
+		size_t n = common_prefix_size(&entry->hash, arg->last);
+		if (n > arg->max)
 			arg->max = n;
-		}
 	}
 	arg->last = &entry->hash;
 }

t/unit-tests/t-reftable-basics.c

@@ -120,7 +120,7 @@ int cmd_main(int argc UNUSED, const char *argv[] UNUSED)
 		for (size_t i = 0; i < ARRAY_SIZE(cases); i++) {
 			check(!reftable_buf_addstr(&a, cases[i].a));
 			check(!reftable_buf_addstr(&b, cases[i].b));
-			check_int(common_prefix_size(&a, &b), ==, cases[i].want);
+			check_uint(common_prefix_size(&a, &b), ==, cases[i].want);
 			reftable_buf_reset(&a);
 			reftable_buf_reset(&b);
 		}