Improve XUNTAG comment

* src/lisp.h (XUNTAG): Shorten (and I hope clarify) new comment.

diff --git a/src/lisp.h b/src/lisp.h
index de6746f1c07b5809bbc56af1699c04f66a74b721..79ce8e5fa8e16dd3346dc592914c0a9fb3bcd9a4 100644 (file)
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -808,10 +808,9 @@ INLINE void
 }
 
 /* Extract A's pointer value, assuming A's Lisp type is TYPE and the
-   extracted pointer's type is CTYPE *.
-   Note that the second term vanishes if EMACS_INT is wider than pointers
-   and the tag is in the upper bits (ie, USE_LSB_TAG=0); this makes
-   untagging slightly cheaper in that case.  */
+   extracted pointer's type is CTYPE *.  When !USE_LSB_TAG this simply
+   extracts A's low-order bits, as (uintptr_t) LISP_WORD_TAG (type) is
+   always zero then.  */
 #define XUNTAG(a, type, ctype) \
   ((ctype *) ((uintptr_t) XLP (a) - (uintptr_t) LISP_WORD_TAG (type)))