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>

1 files changed, 2 insertions, 2 deletions

diff --git a/sha1-lookup.c b/sha1-lookup.c
index 2552b79..4cf3ebd 100644
--- a/sha1-lookup.c
+++ b/sha1-lookup.c
@@ -10,7 +10,7 @@ static uint32_t take2(const unsigned char *sha1)
  * Conventional binary search loop looks like this:
  *
  *      do {
- *              int mi = (lo + hi) / 2;
+ *              int mi = lo + (hi - lo) / 2;
  *              int cmp = "entry pointed at by mi" minus "target";
  *              if (!cmp)
  *                      return (mi is the wanted one)
@@ -95,7 +95,7 @@ int sha1_pos(const unsigned char *sha1, void *table, size_t nr,
 			hi = mi;
 		else
 			lo = mi + 1;
-		mi = (hi + lo) / 2;
+		mi = lo + (hi - lo) / 2;
 	} while (lo < hi);
 	return -lo-1;
 }