fix undefined behavior of testing beyond the end of the iterator

bostick · Oct 29, 2024 · b59c7b6 · b59c7b6
1 parent 18a771e
commit b59c7b6
Showing 1 changed file with 12 additions and 2 deletions.
diff --git a/lib/tbt-parser-util.cpp b/lib/tbt-parser-util.cpp
@@ -375,9 +375,19 @@ zlib_inflate(
 
         ASSERT(it <= end);
 
+        //
+        // it is undefined behavior to test beyond the end of the iterator by doing:
+        // (it + CHUNK <= end)
+        //
+        // however, it is fine to do:
+        // CHUNK <= (end - it)
+        //
+        // (end - it) returns a difference type and may be negative
+        //
+
         if (it == end) {
             break;
-        } else if (it + CHUNK <= end) {
+        } else if (CHUNK <= (end - it)) {
             strm.avail_in = CHUNK;
         } else {
             strm.avail_in = static_cast<uInt>(end - it);
@@ -415,7 +425,7 @@ zlib_inflate(
 
         } while (strm.avail_out == 0);
 
-        if (it + CHUNK < end) {
+        if (CHUNK < (end - it)) {
             strm.avail_in = CHUNK;
             it += CHUNK;
         } else {