From: Mattias Engdegård <mattiase@acm.org>
Date: Wed, 21 Feb 2024 14:22:21 +0000 (+0100)
Subject: ; * src/lisp.h: Add Lisp_Object tagging scheme overview
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=268a4eb1638af4e6ce122123a775804395a8eeba;p=emacs.git

; * src/lisp.h: Add Lisp_Object tagging scheme overview

(cherry picked from commit a2eb123fb606af2a62ad6d0d0162255d7f0601e1)
---

diff --git a/src/lisp.h b/src/lisp.h
index db053ba9f70..b02466390f1 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -478,6 +478,16 @@ typedef EMACS_INT Lisp_Word;
 #endif
 
 
+/* Lisp_Object tagging scheme:
+        Tag location
+   Upper bits  Lower bits  Type        Payload
+   000.......  .......000  symbol      offset from lispsym to struct Lisp_Symbol
+   001.......  .......001  unused
+   01........  ........10  fixnum      signed integer of FIXNUM_BITS
+   110.......  .......011  cons        pointer to struct Lisp_Cons
+   100.......  .......100  string      pointer to struct Lisp_String
+   101.......  .......101  vectorlike  pointer to union vectorlike_header
+   111.......  .......111  float       pointer to struct Lisp_Float  */
 enum Lisp_Type
   {
     /* Symbol.  XSYMBOL (object) points to a struct Lisp_Symbol.  */