X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcompiler%2Fgeneric%2Fearly-objdef.lisp;h=7407e4a400ec89eaf2b1a4ab67e9c50324d559bf;hb=5edd74f6911093805a009a152b32216b3dba59f7;hp=699c30e88d0aaa8bd282b75dbf00d4852c7cea25;hpb=d3df7e8508d37a831ecf06a2c42ddb6ede1d99fa;p=sbcl.git

diff --git a/src/compiler/generic/early-objdef.lisp b/src/compiler/generic/early-objdef.lisp
index 699c30e..7407e4a 100644
--- a/src/compiler/generic/early-objdef.lisp
+++ b/src/compiler/generic/early-objdef.lisp
@@ -14,36 +14,44 @@
 ;;; FIXME: It's clever using :SUFFIX -TYPE for these things, but it's
 ;;; 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-TYPE are defined. Remove the :SUFFIXes and just expand
-;;; out the full names. Or even define them in DEF-FROB EVEN-FIXNUM-TYPE
-;;; style so searches like 'def.*even-fixnum-type' can find them.
+;;; EVEN-FIXNUM-LOWTAG are defined. Remove the :SUFFIXes and just expand
+;;; out the full names. Or even define them in DEF EVEN-FIXNUM-LOWTAG
+;;; style so searches like 'def.*even-fixnum-lowtag' can find them.
 
-;;; the main types. These types are represented by the low three bits
-;;; of the pointer or immediate object.
+;;; 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-TYPE, which is
+  ;; second DEFENUM uses the value of OTHER-IMMEDIATE-0-LOWTAG, which is
   ;; defined in the first DEFENUM. -- AL 20000216
-  (defenum (:suffix -type)
+  (defenum (:suffix -lowtag)
     even-fixnum
-    ;; Note: CMU CL, and SBCL < 0.pre7.39, had FUNCTION-POINTER-TYPE
-    ;; here. We swapped FUNCTION-POINTER-TYPE and
-    ;; INSTANCE-POINTER-TYPE in sbcl-0.pre7.39 in order to help with a
+    ;; Note: CMU CL, and SBCL < 0.pre7.39, had FUN-POINTER-LOWTAG
+    ;; here. We swapped FUN-POINTER-LOWTAG and
+    ;; INSTANCE-POINTER-LOWTAG in sbcl-0.pre7.39 in order to help with a
     ;; low-level pun in the function call sequence on the PPC port.
     ;; For more information, see the PPC port code. -- WHN 2001-10-03
     instance-pointer
     other-immediate-0
     list-pointer
     odd-fixnum
-    function-pointer
+    fun-pointer
     other-immediate-1
     other-pointer))
 
-;;; the heap types. Each of these types is in the header of objects in
-;;; the heap.
-(defenum (:suffix -type
-	  :start (+ (ash 1 lowtag-bits) other-immediate-0-type)
-	  :step (ash 1 (1- lowtag-bits)))
+;;; the heap types, stored in 8 bits of the header of an object on the
+;;; heap, to identify the type of the heap object (which'll be at
+;;; least two machine words, often more)
+(defenum (:suffix -widetag
+	  :start (+ (ash 1 n-lowtag-bits) other-immediate-0-lowtag)
+	  :step (ash 1 (1- n-lowtag-bits)))
   bignum
   ratio
   single-float
@@ -79,14 +87,12 @@
   complex-array
 
   code-header
-  function-header
+  simple-fun-header
   closure-header
   funcallable-instance-header
-  byte-code-function
-  byte-code-closure
-  closure-function-header
-  #!-gengc return-pc-header
-  #!+gengc forwarding-pointer
+  closure-fun-header
+
+  return-pc-header
   value-cell-header
   symbol-header
   base-char
@@ -94,8 +100,7 @@
   unbound-marker
   weak-pointer
   instance-header
-  fdefn
-  )
+  fdefn)
 
 ;;; the different vector subtypes
 (defenum (:prefix vector- :suffix -subtype)