-(file-comment
- "$Header$")
-
-(eval-when (:compile-toplevel :execute :load-toplevel)
-
-(defconstant lowtag-bits 3
- #!+sb-doc
- "Number of bits at the low end of a pointer used for type information.")
-
-(defconstant lowtag-mask (1- (ash 1 lowtag-bits))
- #!+sb-doc
- "Mask to extract the low tag bits from a pointer.")
-
-(defconstant lowtag-limit (ash 1 lowtag-bits)
- #!+sb-doc
- "Exclusive upper bound on the value of the low tag bits from a pointer.")
-
-(defconstant type-bits 8
- #!+sb-doc
- "Number of bits used in the header word of a data block to store the type.")
-
-(defconstant type-mask (1- (ash 1 type-bits))
- #!+sb-doc
- "Mask to extract the type from a header word.")
-
-); eval-when
-
-;;; FIXME: Couldn't/shouldn't these be DEFCONSTANT instead of DEFPARAMETER?
-(defparameter *target-most-positive-fixnum* (1- (ash 1 29))
+;;; the number of bits at the low end of a pointer used for type
+;;; information
+(def!constant n-lowtag-bits
+ (integer-length (1- (/ (* 2 n-word-bits) n-byte-bits))))
+;;; a mask to extract the low tag bits from a pointer
+(def!constant lowtag-mask (1- (ash 1 n-lowtag-bits)))
+;;; the exclusive upper bound on the value of the low tag bits from a
+;;; pointer
+(def!constant lowtag-limit (ash 1 n-lowtag-bits))
+;;; the number of tag bits used for a fixnum
+(def!constant n-fixnum-tag-bits (1- n-lowtag-bits))
+;;; the fixnum tag mask
+(def!constant fixnum-tag-mask (1- (ash 1 n-fixnum-tag-bits)))
+;;; the bit width of positive fixnums
+(def!constant n-positive-fixnum-bits (- n-word-bits n-fixnum-tag-bits 1))
+
+;;; the number of bits used in the header word of a data block to store
+;;; the type
+(def!constant n-widetag-bits 8)
+;;; a mask to extract the type from a data block header word
+(def!constant widetag-mask (1- (ash 1 n-widetag-bits)))
+
+(def!constant sb!xc:most-positive-fixnum
+ (1- (ash 1 (- n-word-bits n-lowtag-bits)))