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 <dsto...@microsoft.com>
---
builtin/index-pack.c | 4 ++--
builtin/pack-objects.c | 2 +-
builtin/unpack-objects.c | 2 +-
cache-tree.c | 2 +-
compat/regex/regex_internal.c | 4 ++--
compat/regex/regexec.c | 2 +-
packfile.c | 2 +-
sha1-lookup.c | 4 ++--
sha1_name.c | 2 +-
string-list.c | 2 +-
utf8.c | 2 +-
xdiff/xpatience.c | 2 +-
12 files changed, 15 insertions(+), 15 deletions(-)
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index f2be145e1..8ec459f52 100644
--- a/builtin/index-pack.c
+++ b/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;
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 5ee2c48ff..6e77dfd44 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1277,7 +1277,7 @@ static int done_pbase_path_pos(unsigned hash)
int lo = 0;
int hi = done_pbase_paths_num;
while (lo < hi) {
- int mi = (hi + lo) / 2;
+ int mi = lo + (hi - lo) / 2;
if (done_pbase_paths[mi] == hash)
return mi;
if (done_pbase_paths[mi] < hash)
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index 689a29fac..62ea264c4 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -394,7 +394,7 @@ static void unpack_delta_entry(enum object_type type,
unsigned long delta_size,
lo = 0;
hi = nr;
while (lo < hi) {
- mid = (lo + hi)/2;
+ mid = lo + (hi - lo) / 2;
if (base_offset < obj_list[mid].offset) {
hi = mid;
} else if (base_offset > obj_list[mid].offset) {
diff --git a/cache-tree.c b/cache-tree.c
index 71d092ed5..d3f740127 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -49,7 +49,7 @@ static int subtree_pos(struct cache_tree *it, const char
*path, int pathlen)
lo = 0;
hi = it->subtree_nr;
while (lo < hi) {
- int mi = (lo + hi) / 2;
+ int mi = lo + (hi - lo) / 2;
struct cache_tree_sub *mdl = down[mi];
int cmp = subtree_name_cmp(path, pathlen,
mdl->name, mdl->namelen);
diff --git a/compat/regex/regex_internal.c b/compat/regex/regex_internal.c
index d4121f2f4..98342b831 100644
--- a/compat/regex/regex_internal.c
+++ b/compat/regex/regex_internal.c
@@ -613,7 +613,7 @@ re_string_reconstruct (re_string_t *pstr, int idx, int
eflags)
int low = 0, high = pstr->valid_len, mid;
do
{
- mid = (high + low) / 2;
+ mid = low + (high - low) / 2;
if (pstr->offsets[mid] > offset)
high = mid;
else if (pstr->offsets[mid] < offset)
@@ -1394,7 +1394,7 @@ re_node_set_contains (const re_node_set *set, int elem)
right = set->nelem - 1;
while (idx < right)
{
- mid = (idx + right) / 2;
+ mid = idx + (right - idx) / 2;
if (set->elems[mid] < elem)
idx = mid + 1;
else
diff --git a/compat/regex/regexec.c b/compat/regex/regexec.c
index 0a745d9c3..6f2b48a78 100644
--- a/compat/regex/regexec.c
+++ b/compat/regex/regexec.c
@@ -4284,7 +4284,7 @@ search_cur_bkref_entry (const re_match_context_t *mctx,
int str_idx)
last = right = mctx->nbkref_ents;
for (left = 0; left < right;)
{
- mid = (left + right) / 2;
+ mid = left + (right - left) / 2;
if (mctx->bkref_ents[mid].str_idx < str_idx)
left = mid + 1;
else
diff --git a/packfile.c b/packfile.c
index eab754248..4a5fe7ab1 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1743,7 +1743,7 @@ off_t find_pack_entry_one(const unsigned char *sha1,
sha1[0], sha1[1], sha1[2], lo, hi, p->num_objects);
while (lo < hi) {
- unsigned mi = (lo + hi) / 2;
+ unsigned mi = lo + (hi - lo) / 2;
int cmp = hashcmp(index + mi * stride, sha1);
if (debug_lookup)
diff --git a/sha1-lookup.c b/sha1-lookup.c
index 2552b7902..4cf3ebd92 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;
}
diff --git a/sha1_name.c b/sha1_name.c
index 134ac9742..c7c5ab376 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -157,7 +157,7 @@ static void unique_in_pack(struct packed_git *p,
num = p->num_objects;
last = num;
while (first < last) {
- uint32_t mid = (first + last) / 2;
+ uint32_t mid = first + (last - first) / 2;
const unsigned char *current;
int cmp;
diff --git a/string-list.c b/string-list.c
index 806b4c872..a0cf0cfe8 100644
--- a/string-list.c
+++ b/string-list.c
@@ -16,7 +16,7 @@ static int get_entry_index(const struct string_list *list,
const char *string,
compare_strings_fn cmp = list->cmp ? list->cmp : strcmp;
while (left + 1 < right) {
- int middle = (left + right) / 2;
+ int middle = left + (right - left) / 2;
int compare = cmp(string, list->items[middle].string);
if (compare < 0)
right = middle;
diff --git a/utf8.c b/utf8.c
index 47a42047c..2c27ce013 100644
--- a/utf8.c
+++ b/utf8.c
@@ -32,7 +32,7 @@ static int bisearch(ucs_char_t ucs, const struct interval
*table, int max)
if (ucs < table[0].first || ucs > table[max].last)
return 0;
while (max >= min) {
- mid = (min + max) / 2;
+ mid = min + (max - min) / 2;
if (ucs > table[mid].last)
min = mid + 1;
else if (ucs < table[mid].first)
diff --git a/xdiff/xpatience.c b/xdiff/xpatience.c
index a613efc70..9f91702de 100644
--- a/xdiff/xpatience.c
+++ b/xdiff/xpatience.c
@@ -166,7 +166,7 @@ static int binary_search(struct entry **sequence, int
longest,
int left = -1, right = longest;
while (left + 1 < right) {
- int middle = (left + right) / 2;
+ int middle = left + (right - left) / 2;
/* by construction, no two entries can be equal */
if (sequence[middle]->line2 > entry->line2)
right = middle;
--
2.14.1.538.g56ec8fc98.dirty
