;;;; 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. (in-package "SB!VM") ;;; Tags for the main low-level types are stored in the low n (usually 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 + N-WORD-BYTES = 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. ;;; * OTHER-IMMEDIATE-0-LOWTAG are spaced 4 apart: various code wants to ;;; iterate through these ;;; * Allocation code on Alpha wants lowtags for heap-allocated ;;; objects to be odd. ;;; (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.:-) ;;; ;;; Another way to look at lowtags is that there is no one lowtag ;;; length. On 32-bit platforms, fixnums and other-immediates have a ;;; lowtag length of two bits, and pointers have a lowtag length of ;;; three bits. On 64-bit platforms, fixnums and pointers gain an ;;; extra bit, and six "pad" lowtags waste the extra encoding space so ;;; obtained. ;;; ;;; x00 -- fixnum ;;; x10 -- other-immediate ;;; 001 -- instance-pointer ;;; 011 -- list-pointer ;;; 101 -- fun-pointer ;;; 111 -- other-pointer ;;; ;;; If you change the tag layout, check the various functions in ;;; src/runtime/runtime.h to see if they need to be updated, along ;;; with print_obj() in src/runtime/print.c, possibly gc_init_tables() ;;; in src/runtime/gc-common-c and possibly the code in src/code/room. (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 #!+#.(cl:if (cl:= 64 sb!vm:n-word-bits) '(and) '(or)) (defenum () even-fixnum-lowtag other-immediate-0-lowtag pad0-lowtag instance-pointer-lowtag pad1-lowtag other-immediate-1-lowtag pad2-lowtag list-pointer-lowtag odd-fixnum-lowtag other-immediate-2-lowtag pad3-lowtag fun-pointer-lowtag pad4-lowtag other-immediate-3-lowtag pad5-lowtag other-pointer-lowtag) #!+#.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) (defenum () even-fixnum-lowtag instance-pointer-lowtag other-immediate-0-lowtag list-pointer-lowtag odd-fixnum-lowtag fun-pointer-lowtag other-immediate-1-lowtag other-pointer-lowtag)) (def!constant nil-value (+ static-space-start n-word-bytes other-pointer-lowtag)) (defconstant-eqx fixnum-lowtags #.(let ((fixtags nil)) (do-external-symbols (sym "SB!VM") (let* ((name (symbol-name sym)) (len (length name))) (when (and (boundp sym) (integerp (symbol-value sym)) (> len 7) (string= name "-LOWTAG" :start1 (- len 7)) (zerop (logand (symbol-value sym) fixnum-tag-mask))) (push sym fixtags)))) `',(sort fixtags #'string< :key #'symbol-name)) #'equal) ;;; 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 (;; The first widetag must be greater than SB!VM:LOWTAG-LIMIT ;; otherwise code in generic/early-type-vops will suffer ;; a long, horrible death. --njf, 2004-08-09 :start (+ (ash 1 n-lowtag-bits) other-immediate-0-lowtag) :step 4) ;; NOTE: the binary numbers off to the side are only valid for 32-bit ;; ports; add #b1000 if you want to know the values for 64-bit ports. ;; And note that the numbers get a little scrambled further down. ;; --njf, 2004-08-09 bignum-widetag ; 00001010 ratio-widetag ; 00001110 single-float-widetag ; 00010010 double-float-widetag ; 00010110 complex-widetag ; 00011010 complex-single-float-widetag ; 00011110 complex-double-float-widetag ; 00100010 code-header-widetag ; 00100110 simple-fun-header-widetag ; 00101010 closure-header-widetag ; 00101110 funcallable-instance-header-widetag ; 00110010 return-pc-header-widetag ; 00110110 value-cell-header-widetag ; 00111010 symbol-header-widetag ; 00111110 character-widetag ; 01000010 sap-widetag ; 01000110 unbound-marker-widetag ; 01001010 weak-pointer-widetag ; 01001110 instance-header-widetag ; 01010010 fdefn-widetag ; 01010110 no-tls-value-marker-widetag ; 01011010 unused01-widetag ; 01011110 unused02-widetag ; 01100010 unused03-widetag ; 01100110 unused04-widetag ; 01101010 unused05-widetag ; 01101110 unused06-widetag ; 01110010 unused07-widetag ; 01110110 #!+#.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) unused08-widetag ; 01111010 #!+#.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) unused09-widetag ; 01111110 #!+#.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) unused10-widetag ; 10000010 #!+#.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) unused11-widetag ; 10000110 simple-array-unsigned-byte-2-widetag ; 10001010 simple-array-unsigned-byte-4-widetag ; 10001110 simple-array-unsigned-byte-7-widetag ; 10010010 simple-array-unsigned-byte-8-widetag ; 10010110 simple-array-unsigned-byte-15-widetag ; 10011010 simple-array-unsigned-byte-16-widetag ; 10011110 simple-array-nil-widetag ; 10100010 simple-base-string-widetag ; 10100110 #!+sb-unicode simple-character-string-widetag simple-bit-vector-widetag ; 10101010 simple-vector-widetag ; 10101110 #!+#.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) simple-array-unsigned-fixnum-widetag ; 10110010 simple-array-unsigned-byte-31-widetag ; 10110110 simple-array-unsigned-byte-32-widetag ; 10111010 #!+#.(cl:if (cl:= 64 sb!vm:n-word-bits) '(and) '(or)) simple-array-unsigned-fixnum-widetag #!+#.(cl:if (cl:= 64 sb!vm:n-word-bits) '(and) '(or)) simple-array-unsigned-byte-63-widetag #!+#.(cl:if (cl:= 64 sb!vm:n-word-bits) '(and) '(or)) simple-array-unsigned-byte-64-widetag simple-array-signed-byte-8-widetag ; 10111110 simple-array-signed-byte-16-widetag ; 11000010 #!+#.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) simple-array-fixnum-widetag ; 11000110 simple-array-signed-byte-32-widetag ; 11001010 #!+#.(cl:if (cl:= 64 sb!vm:n-word-bits) '(and) '(or)) simple-array-fixnum-widetag #!+#.(cl:if (cl:= 64 sb!vm:n-word-bits) '(and) '(or)) simple-array-signed-byte-64-widetag simple-array-single-float-widetag ; 11001110 simple-array-double-float-widetag ; 11010010 simple-array-complex-single-float-widetag ; 11010110 simple-array-complex-double-float-widetag ; 11011010 simple-array-widetag ; 11011110 complex-vector-nil-widetag ; 11100010 complex-base-string-widetag ; 11100110 #!+sb-unicode complex-character-string-widetag complex-bit-vector-widetag ; 11101010 complex-vector-widetag ; 11101110 complex-array-widetag ; 11110010 #!+#.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) unused12-widetag ; 11110110 #!+(and #.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) (not sb-unicode)) unused13-widetag ; 11111010 #!+(and #.(cl:if (cl:= 32 sb!vm:n-word-bits) '(and) '(or)) (not sb-unicode)) unused14-widetag ; 11111110 ) ;;; the different vector subtypes (defenum () vector-normal-subtype vector-unused-subtype vector-valid-hashing-subtype)