Add mask

Author: clementval

flang/include/flang/ISO_Fortran_binding.h

@@ -154,6 +154,8 @@ extern "C++" template <typename T> struct FlexibleArray : T {
 #define _CFI_ADDENDUM_BITS 1
 /* Value of the addendum presence flag */
 #define _CFI_ADDENDUM_FLAG 1
+/* Allocator index mask */
+#define _CFI_ALLOCATOR_IDX_MASK 0b00001110
 
 typedef struct CFI_cdesc_t {
   _CFI_CDESC_T_HEADER_MEMBERS
@@ -169,9 +171,10 @@ typedef struct CFI_cdesc_t {
   }
   RT_API_ATTRS inline void SetHasAddendum() { extra |= _CFI_ADDENDUM_FLAG; }
   RT_API_ATTRS inline int GetAllocIdx() const {
-    return ((int)extra >> _CFI_ADDENDUM_BITS);
+    return (extra & _CFI_ALLOCATOR_IDX_MASK) >> _CFI_ADDENDUM_BITS;
   }
   RT_API_ATTRS inline void SetAllocIdx(int pos) {
+    extra &= ~_CFI_ALLOCATOR_IDX_MASK; // Clear the allocator index bits.
     extra |= (pos << _CFI_ADDENDUM_BITS);
   }
 #endif