Merge #12973 itertools fix.
diff --git a/Misc/NEWS b/Misc/NEWS
index 0e18621..4f55034 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -17,9 +17,9 @@
- Issue #13021: Missing decref on an error path. Thanks to Suman Saha for
finding the bug and providing a patch.
-- Issue #12973: Fix overflow check that relied on undefined behaviour in
- list_repeat. This bug caused test_list to fail with recent versions
- of Clang.
+- Issue #12973: Fix overflow checks that relied on undefined behaviour in
+ list_repeat (listobject.c) and islice_next (itertoolsmodule.c). These bugs
+ caused test failures with recent versions of Clang.
- Issue #12904: os.utime, os.futimes, os.lutimes, and os.futimesat now write
atime and mtime with nanosecond precision on modern POSIX platforms.
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index ad22ec7..d0897c3 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -1234,7 +1234,9 @@
return NULL;
lz->cnt++;
oldnext = lz->next;
- lz->next += lz->step;
+ /* The (size_t) cast below avoids the danger of undefined
+ behaviour from signed integer overflow. */
+ lz->next += (size_t)lz->step;
if (lz->next < oldnext || (stop != -1 && lz->next > stop))
lz->next = stop;
return item;