;;; 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)
+;;;
+;;; Note: the order specified here is not critical for correctness,
+;;; but (FIXME) with %TEST-HEADERS as currently defined, BIGNUM must
+;;; be first, and COMPLEX-ARRAY must be last.
+;;;
+;;; However, for efficiency, we prefer contiguous sets of widetags for
+;;; "similar" objects, so that type checking can be done with a range
+;;; check, rather than several individual checks.
+;;;
+;;; * BIGNUM + RATIO (+ FIXNUM) = RATIONAL
+;;;
+;;; * SINGLE-FLOAT + DOUBLE-FLOAT + LONG-FLOAT = FLOAT
+;;;
+;;; * RATIONAL + FLOAT = REAL
+;;;
+;;; * (FIXME: COMPLEX example, which needs fixing anyway -- see
+;;; UPGRADED-COMPLEX-PART-TYPE)
+;;;
+;;; * SIMPLE-ARRAY-* = (SIMPLE-ARRAY * (*))
+;;;
+;;; * SIMPLE-ARRAY-NIL + SIMPLE-BASE-STRING = SIMPLE-STRING
+;;;
+;;; * SIMPLE-ARRAY + COMPLEX-ARRAYOID = (SATISFIES ARRAY-HEADER-P)
+;;;
+;;; In addition, with
+;;; sufficient care we can cause extra combinations to appear with
+;;; differences in only one bit, permitting a more efficient type
+;;; test. As an example, if SIMPLE-BASE-STRING = 0xA6 and
+;;; COMPLEX-BASE-STRING = 0xE6, then the type test for BASE-STRING is
+;;;
+;;; AND tag, ~0x40, tag
+;;; ANDcc tag, 0xA6, tag
+;;; JNE tag, label
+;;;
+;;; rather than two separate tests and jumps
(defenum (:suffix -widetag
:start (+ (ash 1 n-lowtag-bits) other-immediate-0-lowtag)
:step (ash 1 (1- n-lowtag-bits)))
complex-double-float
#!+long-float complex-long-float
- simple-array
- simple-string
- simple-bit-vector
- simple-vector
+ code-header
+ simple-fun-header
+ closure-header
+ funcallable-instance-header
+
+ return-pc-header
+ value-cell-header
+ symbol-header
+ base-char
+ sap
+ unbound-marker
+ weak-pointer
+ instance-header
+ fdefn
+
+ unused00
+ unused01
+ unused02
+ unused03
+ unused04
+ unused05
+ unused06
+ unused07
+ #!-long-float unused08
+ #!-long-float unused09
+
+ #!+long-float simple-array-long-float
+ #!+long-float simple-array-complex-long-float
+ #!-long-float unused10
+ #!-long-float unused11
+
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-nil
+ simple-base-string
+ simple-bit-vector
+ simple-vector
+ 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-signed-byte-32
simple-array-single-float
simple-array-double-float
- #!+long-float simple-array-long-float
simple-array-complex-single-float
simple-array-complex-double-float
- #!+long-float simple-array-complex-long-float
- complex-string
+ simple-array
+ complex-vector-nil
+ complex-base-string
complex-bit-vector
complex-vector
complex-array
-
- code-header
- simple-fun-header
- closure-header
- funcallable-instance-header
- closure-fun-header
-
- return-pc-header
- value-cell-header
- symbol-header
- base-char
- sap
- unbound-marker
- weak-pointer
- instance-header
- fdefn)
+)
;;; the different vector subtypes
(defenum (:prefix vector- :suffix -subtype)
projects / sbcl.git / blobdiff