cleanup: fix possible overflow errors in binary search

A common mistake when writing binary search is to allow possible
integer overflow by using the simple average:

	mid = (min + max) / 2;

Instead, use the overflow-safe version:

	mid = min + (max - min) / 2;

This translation is safe since the operation occurs inside a loop
conditioned on "min < max". The included changes were found using
the following git grep:

	git grep '/ *2;' '*.c'

Making this cleanup will prevent future review friction when a new
binary search is contructed based on existing code.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/index-pack.c

@@ -633,7 +633,7 @@ static int find_ofs_delta(const off_t offset, enum object_type type)
 	int first = 0, last = nr_ofs_deltas;
 
 	while (first < last) {
-		int next = (first + last) / 2;
+		int next = first + (last - first) / 2;
 		struct ofs_delta_entry *delta = &ofs_deltas[next];
 		int cmp;
 
@@ -687,7 +687,7 @@ static int find_ref_delta(const unsigned char *sha1, enum object_type type)
 	int first = 0, last = nr_ref_deltas;
 
 	while (first < last) {
-		int next = (first + last) / 2;
+		int next = first + (last - first) / 2;
 		struct ref_delta_entry *delta = &ref_deltas[next];
 		int cmp;