[PATCH] hamt: fix technically undefined behavior

[Marc Nieper-Wißkirchen]

Bug reported by Bruno Haible in
<https://lists.gnu.org/r/bug-gnulib/2022-04/msg00023.html>.
* lib/hamt.c (entry_insert): Remove technically undefined
behavior when shifting an integer of N bits by N or more bits.
---
 ChangeLog  | 8 ++++++++
 lib/hamt.c | 5 +++++
 2 files changed, 13 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index ccf4acd03..0d04cb70e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2022-08-12  Marc Nieper-Wißkirchen  <marc@nieper-wisskirchen.de>
+
+       hamt: fix technically undefined behavior
+       Bug reported by Bruno Haible in
+       <https://lists.gnu.org/r/bug-gnulib/2022-04/msg00023.html>.
+       * lib/hamt.c (entry_insert): Remove technically undefined
+       behavior when shifting an integer of N bits by N or more bits.
+
 2022-08-10  Paul Eggert  <eggert@cs.ucla.edu>
 
        stdckdint: fix dependency
diff --git a/lib/hamt.c b/lib/hamt.c
index 2b07cf23b..be9712561 100644
--- a/lib/hamt.c
+++ b/lib/hamt.c
@@ -680,6 +680,11 @@ entry_insert (const struct function_table *functions, 
Hamt_entry *entry,
       Hamt_entry *new_entry = copy_entry (*elt_ptr);
       if (replace)
         *elt_ptr = NULL;
+      /* We have to take this shortcut as shifting an integer of N
+        bits by N or more bits triggers undefined behavior.
+        See: 
https://lists.gnu.org/archive/html/bug-gnulib/2022-04/msg00023.html.  */
+      if (depth >= _GL_HAMT_MAX_DEPTH)
+       return (Hamt_entry *) create_populated_bucket (new_entry, copy_entry 
(entry));
       return create_populated_subtrie (new_entry, copy_entry (entry), hash,
                                        (hash_element (functions, entry)
                                         >> (5 * depth)), depth);
-- 
2.34.1