;;; 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-FROB EVEN-FIXNUM-LOWTAG
+;;; 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, to be stored in the low three
-;;; bits to identify the type of a machine word
+;;; 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
;;; 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 -type
- :start (+ (ash 1 lowtag-bits) other-immediate-0-lowtag)
- :step (ash 1 (1- lowtag-bits)))
+(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-unsigned-byte-4
+ simple-array-unsigned-byte-7
simple-array-unsigned-byte-8
+ simple-array-unsigned-byte-15
simple-array-unsigned-byte-16
+ simple-array-unsigned-byte-29
+ simple-array-unsigned-byte-31
simple-array-unsigned-byte-32
simple-array-signed-byte-8
simple-array-signed-byte-16
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