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master e942581488a: Improve XUNTAG comment
From: |
Paul Eggert |
Subject: |
master e942581488a: Improve XUNTAG comment |
Date: |
Mon, 18 Sep 2023 17:11:26 -0400 (EDT) |
branch: master
commit e942581488a139eaf82d77f4d430cf18ace6c728
Author: Paul Eggert <eggert@cs.ucla.edu>
Commit: Paul Eggert <eggert@cs.ucla.edu>
Improve XUNTAG comment
* src/lisp.h (XUNTAG): Shorten (and I hope clarify) new comment.
---
src/lisp.h | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/src/lisp.h b/src/lisp.h
index de6746f1c07..79ce8e5fa8e 100644
--- 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)))
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