;;;; type-based constants
;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.
;;; 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-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.
;;; Tags for the main low-level types are stored in the low three
;;; bits to identify the type of a machine word. Certain constraints
;;; * 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
;;; * OTHER-POINTER-LOWTAG > 4: Some code in the SPARC backend,
;;; which uses bit 2 of the ALLOC register to indicate that
;;; PSEUDO-ATOMIC is on, doesn't strip the low bits of reg_ALLOC
;;; before ORing in OTHER-POINTER-LOWTAG within a PSEUDO-ATOMIC
;;; (These are just the ones we know about as of sbcl-0.7.1.22. There
;;; might easily be more, since these values have stayed highly
;;; constrained for more than a decade, an inviting target for
;;; inventive abstraction-phobic maintainers.:-)
(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
;; defined in the first DEFENUM. -- AL 20000216
(defenum (:suffix -lowtag)
;; 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
;;; 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)))
;;; the different vector subtypes
(defenum (:prefix vector- :suffix -subtype)