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authorDerrick Stolee <dstolee@microsoft.com>2017-10-08 14:29:37 -0400
committerJunio C Hamano <gitster@pobox.com>2017-10-10 08:57:24 +0900
commit19716b21a4255ecc7148b54ab2c78039c59f25bf (patch)
tree5f1cecbffc543c64e7c4c4f371d204424e1ce1bb
parent217f2767cbcb562872437eed4dec62e00846d90c (diff)
downloadgit-19716b21a4255ecc7148b54ab2c78039c59f25bf.tar.gz
cleanup: fix possible overflow errors in binary searchds/avoid-overflow-in-midpoint-computation
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>
-rw-r--r--builtin/index-pack.c4
-rw-r--r--builtin/pack-objects.c2
-rw-r--r--builtin/unpack-objects.c2
-rw-r--r--cache-tree.c2
-rw-r--r--compat/regex/regex_internal.c4
-rw-r--r--compat/regex/regexec.c2
-rw-r--r--packfile.c2
-rw-r--r--sha1-lookup.c4
-rw-r--r--sha1_name.c2
-rw-r--r--string-list.c2
-rw-r--r--utf8.c2
-rw-r--r--xdiff/xpatience.c2
12 files changed, 15 insertions, 15 deletions
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index f2be145e12..8ec459f522 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 5ee2c48ffb..6e77dfd444 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 689a29fac1..62ea264c46 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 71d092ed51..d3f7401278 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 d4121f2f4f..98342b8316 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 0a745d9c3b..6f2b48a78b 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 eab7542487..4a5fe7ab18 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 2552b7902c..4cf3ebd921 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 134ac9742f..c7c5ab376c 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 806b4c8723..a0cf0cfe88 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 47a42047c8..2c27ce0137 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 a613efc703..9f91702de7 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;