diff --git a/compiler/generic/objdef.lisp b/compiler/generic/objdef.lisp
index 97f20c7cc515c7a6ea4ff08836f6e81d9bd01749..95a684dd93090cb3f09f81abd289b454945a7dfc 100644
--- a/compiler/generic/objdef.lisp
+++ b/compiler/generic/objdef.lisp
@@ -5,7 +5,7 @@
 ;;; Carnegie Mellon University, and has been placed in the public domain.
 ;;;
 (ext:file-comment
-  "$Header: /Volumes/share2/src/cmucl/cvs2git/cvsroot/src/compiler/generic/objdef.lisp,v 1.46 2002/09/03 16:29:45 toy Exp $")
+  "$Header: /Volumes/share2/src/cmucl/cvs2git/cvsroot/src/compiler/generic/objdef.lisp,v 1.47 2002/09/04 11:21:02 toy Exp $")
 ;;;
 ;;; **********************************************************************
 ;;;
@@ -65,6 +65,16 @@
 
 (eval-when (compile eval load)
 
+(defconstant lowtag-bits 3
+  "Number of bits at the low end of a pointer used for type information.")
+
+(defconstant lowtag-mask (1- (ash 1 lowtag-bits))
+  "Mask to extract the low tag bits from a pointer.")
+  
+(defconstant lowtag-limit (ash 1 lowtag-bits)
+  "Exclusive upper bound on the value of the low tag bits from a
+  pointer.")
+  
 (defconstant type-bits 8
   "Number of bits used in the header word of a data block for typeing.")