;;; 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 figure out where things like EVEN-FIXNUM type are
-;;; defined. Remove the :SUFFIXes and just expand out the full names.
+;;; 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.
-;;; the main types. These types are represented by the low three bits of the
-;;; pointer or immeditate object.
-(defenum (:suffix -type)
- even-fixnum
- function-pointer
- other-immediate-0
- list-pointer
- odd-fixnum
- instance-pointer
- other-immediate-1
- other-pointer)
+;;; 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
+;;; * 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
+;;; section.
+;;; (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)
+ even-fixnum
+ ;; 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
+ 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
#!+long-float complex-long-float
simple-array
- simple-string
+ simple-array-nil
+ simple-base-string
simple-bit-vector
simple-vector
simple-array-unsigned-byte-2
simple-array-complex-single-float
simple-array-complex-double-float
#!+long-float simple-array-complex-long-float
- complex-string
+ complex-base-string
+ complex-vector-nil
complex-bit-vector
complex-vector
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
unbound-marker
weak-pointer
instance-header
- fdefn
- )
+ fdefn)
;;; the different vector subtypes
(defenum (:prefix vector- :suffix -subtype)
projects / sbcl.git / blobdiff