X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcompiler%2Fgeneric%2Fearly-objdef.lisp;h=7407e4a400ec89eaf2b1a4ab67e9c50324d559bf;hb=5edd74f6911093805a009a152b32216b3dba59f7;hp=e713b892f0dd6a95811369c0d40ff2aa86c72a9f;hpb=3c65762b927af861c9c8bc416e4cbac9a14ec0c3;p=sbcl.git

diff --git a/src/compiler/generic/early-objdef.lisp b/src/compiler/generic/early-objdef.lisp
index e713b89..7407e4a 100644
--- a/src/compiler/generic/early-objdef.lisp
+++ b/src/compiler/generic/early-objdef.lisp
@@ -15,11 +15,18 @@
 ;;; a pain for people just learning to find their way around the code
 ;;; who want to use lexical search to figure out where things like
 ;;; EVEN-FIXNUM-LOWTAG are defined. Remove the :SUFFIXes and just expand
-;;; out the full names. Or even define them in DEF-FROB EVEN-FIXNUM-LOWTAG
+;;; out the full names. Or even define them in DEF EVEN-FIXNUM-LOWTAG
 ;;; style so searches like 'def.*even-fixnum-lowtag' can find them.
 
-;;; tags for the main low-level types, to be stored in the low three
-;;; bits to identify the type of a machine word 
+;;; Tags for the main low-level types are stored in the low three
+;;; bits to identify the type of a machine word.  Certain constraints 
+;;; apply:
+;;;   * EVEN-FIXNUM-LOWTAG and ODD-FIXNUM-LOWTAG must be 0 and 4: code
+;;;     which shifts left two places to convert raw integers to tagged
+;;;     fixnums is ubiquitous.
+;;;   * LIST-POINTER-LOWTAG + 4 = OTHER-POINTER-LOWTAG: NIL is both a
+;;;     cons and a symbol (at the same address) and depends on this.
+;;;     See the definition of SYMBOL in objdef.lisp
 (eval-when (:compile-toplevel :load-toplevel :execute)
   ;; The EVAL-WHEN is necessary (at least for Lispworks), because the
   ;; second DEFENUM uses the value of OTHER-IMMEDIATE-0-LOWTAG, which is