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 (1- n-lowtag-bits))
  23 ;;; the fixnum tag mask
  24 (def!constant fixnum-tag-mask (1- (ash 1 n-fixnum-tag-bits)))
  25 ;;; the bit width of positive fixnums
  26 (def!constant n-positive-fixnum-bits (- n-word-bits n-fixnum-tag-bits 1))
  27
  28 ;;; the number of bits to shift between word addresses and byte addresses
  29 (def!constant word-shift (1- (integer-length (/ n-word-bits n-byte-bits))))
  30
  31 ;;; the number of bytes in a word
  32 (def!constant n-word-bytes (/ n-word-bits n-byte-bits))
  33
  34 ;;; the number of bits used in the header word of a data block to store
  35 ;;; the type
  36 (def!constant n-widetag-bits 8)
  37 ;;; a mask to extract the type from a data block header word
  38 (def!constant widetag-mask (1- (ash 1 n-widetag-bits)))
  39
  40 (def!constant sb!xc:most-positive-fixnum
  41     (1- (ash 1 (- n-word-bits n-lowtag-bits)))
  42   #!+sb-doc
  43   "the fixnum closest in value to positive infinity")
  44 (def!constant sb!xc:most-negative-fixnum
  45     (ash -1 (- n-word-bits n-lowtag-bits))
  46   #!+sb-doc
  47   "the fixnum closest in value to negative infinity")
  48
  49 (def!constant most-positive-exactly-single-float-fixnum
  50   (min #xffffff most-positive-fixnum))
  51 (def!constant most-negative-exactly-single-float-fixnum
  52   (max #x-ffffff most-negative-fixnum))
  53 (def!constant most-positive-exactly-double-float-fixnum
  54   (min #x1fffffffffffff most-positive-fixnum))
  55 (def!constant most-negative-exactly-double-float-fixnum
  56   (max #x-1fffffffffffff most-negative-fixnum))