1 files changed, 13 insertions, 9 deletions

diff --git a/src/alloc.c b/src/alloc.c
index ccd5a847dad..5776a2be927 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -107,10 +107,15 @@ Lisp_Object memory_signal_data;
 #define MAX_SAVE_STACK 16000
 #endif
 
-/* Define DONT_COPY_FLAG to be the bit in a small string that was placed
-   in the low bit of the size field when marking small strings.  */
+/* Define DONT_COPY_FLAG to be some bit which will always be zero in a
+   pointer to a Lisp_Object, when that pointer is viewed as an integer.
+   (On most machines, pointers are even, so we can use the low bit.
+   Word-addressible architectures may need to override this in the m-file.)
+   When linking references to small strings through the size field, we
+   use this slot to hold the bit that would otherwise be interpreted as
+   the GC mark bit.  */
 #ifndef DONT_COPY_FLAG
-#define DONT_COPY_FLAG PSEUDOVECTOR_FLAG
+#define DONT_COPY_FLAG 1
 #endif /* no DONT_COPY_FLAG  */
 
 /* Buffer in which we save a copy of the C stack at each GC.  */
@@ -1509,8 +1514,7 @@ mark_object (objptr)
           {
             /* A small string.  Put this reference
                into the chain of references to it.
-               The address OBJPTR is even, so if the address
-               includes MARKBIT, put it in the low bit
+               If the address includes MARKBIT, put that bit elsewhere
                when we store OBJPTR into the size field.  */
 
             if (XMARKBIT (*objptr))
@@ -1523,9 +1527,9 @@ mark_object (objptr)
 
             if ((EMACS_INT) objptr & DONT_COPY_FLAG)
               abort ();
-            ptr->size = (EMACS_INT) objptr & ~MARKBIT;
-            if ((EMACS_INT) objptr & MARKBIT)
-              ptr->size |= DONT_COPY_FLAG;
+            ptr->size = (EMACS_INT) objptr;
+            if (ptr->size & MARKBIT)
+              ptr->size ^= MARKBIT | DONT_COPY_FLAG;
           }
       }
       break;
@@ -2043,7 +2047,7 @@ gc_sweep ()
         if (s->size & ARRAY_MARK_FLAG)
           {
             ((struct Lisp_String *)(&sb->chars[0]))->size
-              &= ~ARRAY_MARK_FLAG & ~MARKBIT & ~DONT_COPY_FLAG;
+              &= ~ARRAY_MARK_FLAG & ~MARKBIT;
             UNMARK_BALANCE_INTERVALS (s->intervals);
             total_string_size += ((struct Lisp_String *)(&sb->chars[0]))->size;
             prev = sb, sb = sb->next;