src/compiler/generic/early-vm.lisp

   1 ;;;; This software is part of the SBCL system. See the README file for
   2 ;;;; more information.
   3 ;;;;
   4 ;;;; This software is derived from the CMU CL system, which was
   5 ;;;; written at Carnegie Mellon University and released into the
   6 ;;;; public domain. The software is in the public domain and is
   7 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
   8 ;;;; files for more information.
   9
  10 (in-package "SB!VM")
  11
  12 ;;; the number of bits at the low end of a pointer used for type
  13 ;;; information
  14 (def!constant n-lowtag-bits
  15   (integer-length (1- (/ (* 2 n-word-bits) n-byte-bits))))
  16 ;;; a mask to extract the low tag bits from a pointer
  17 (def!constant lowtag-mask (1- (ash 1 n-lowtag-bits)))
  18 ;;; the exclusive upper bound on the value of the low tag bits from a
  19 ;;; pointer
  20 (def!constant lowtag-limit (ash 1 n-lowtag-bits))
  21 ;;; the number of tag bits used for a fixnum
  22 (def!constant n-fixnum-tag-bits
  23   ;; On 64-bit targets, this may be as low as 1 (for 63-bit
  24   ;; fixnums) and as high as 3 (for 61-bit fixnums).  The
  25   ;; constraint on the low end is that we need at least one bit
  26   ;; to determine if a value is a fixnum or not, and the
  27   ;; constraint on the high end is that it must not exceed
  28   ;; WORD-SHIFT (defined below) due to the use of unboxed
  29   ;; word-aligned byte pointers as boxed values in various
  30   ;; places.  FIXME: This should possibly be exposed for
  31   ;; configuration via customize-target-features.
  32   #!+64-bit 1
  33   ;; On 32-bit targets, this may be as low as 2 (for 30-bit
  34   ;; fixnums) and as high as 2 (for 30-bit fixnums).  The
  35   ;; constraint on the low end is simple overcrowding of the
  36   ;; lowtag space, and the constraint on the high end is that it
  37   ;; must not exceed WORD-SHIFT.
  38   #!-64-bit (1- n-lowtag-bits))
  39 ;;; the fixnum tag mask
  40 (def!constant fixnum-tag-mask (1- (ash 1 n-fixnum-tag-bits)))
  41 ;;; the bit width of fixnums
  42 (def!constant n-fixnum-bits (- n-word-bits n-fixnum-tag-bits))
  43 ;;; the bit width of positive fixnums
  44 (def!constant n-positive-fixnum-bits (1- n-fixnum-bits))
  45
  46 ;;; the number of bits to shift between word addresses and byte addresses
  47 (def!constant word-shift (1- (integer-length (/ n-word-bits n-byte-bits))))
  48
  49 ;;; the number of bytes in a word
  50 (def!constant n-word-bytes (/ n-word-bits n-byte-bits))
  51
  52 ;;; the number of bytes in a machine word
  53 (def!constant n-machine-word-bytes (/ n-machine-word-bits n-byte-bits))
  54
  55 ;;; the number of bits used in the header word of a data block to store
  56 ;;; the type
  57 (def!constant n-widetag-bits 8)
  58 ;;; a mask to extract the type from a data block header word
  59 (def!constant widetag-mask (1- (ash 1 n-widetag-bits)))
  60
  61 (def!constant sb!xc:most-positive-fixnum
  62     (1- (ash 1 n-positive-fixnum-bits))
  63   #!+sb-doc
  64   "the fixnum closest in value to positive infinity")
  65 (def!constant sb!xc:most-negative-fixnum
  66     (ash -1 n-positive-fixnum-bits)
  67   #!+sb-doc
  68   "the fixnum closest in value to negative infinity")
  69
  70 (def!constant most-positive-word (1- (expt 2 n-word-bits))
  71   #!+sb-doc
  72   "The most positive integer that is of type SB-EXT:WORD.")
  73
  74 (def!constant most-positive-exactly-single-float-fixnum
  75   (min #xffffff sb!xc:most-positive-fixnum))
  76 (def!constant most-negative-exactly-single-float-fixnum
  77   (max #x-ffffff sb!xc:most-negative-fixnum))
  78 (def!constant most-positive-exactly-double-float-fixnum
  79   (min #x1fffffffffffff sb!xc:most-positive-fixnum))
  80 (def!constant most-negative-exactly-double-float-fixnum
  81   (max #x-1fffffffffffff sb!xc:most-negative-fixnum))
  82
  83 ;;;; Point where continuous area starting at dynamic-space-start bumps into
  84 ;;;; next space.
  85 #!+gencgc
  86 (def!constant max-dynamic-space-end
  87     (let ((stop (1- (ash 1 n-word-bits)))
  88           (start dynamic-space-start))
  89       (dolist (other-start (list read-only-space-start static-space-start
  90                                  #!+linkage-table
  91                                  linkage-table-space-start))
  92         (declare (notinline <)) ; avoid dead code note
  93         (when (< start other-start)
  94           (setf stop (min stop other-start))))
  95       stop))
  96
  97 ;; The lowest index that you can pass to %INSTANCE-REF accessing
  98 ;; a slot of data that is not the instance-layout.
  99 ;; To get a layout, you must call %INSTANCE-LAYOUT - don't assume index 0.
 100 (def!constant instance-data-start 1)
 101
 102 ;;; Is X a fixnum in the target Lisp?
 103 #+sb-xc-host
 104 (defun fixnump (x)
 105   (and (integerp x)
 106        (<= sb!xc:most-negative-fixnum x sb!xc:most-positive-fixnum)))