1 ;;;; This software is part of the SBCL system. See the README file for
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.
12 ;;; the number of bits at the low end of a pointer used for type
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
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))
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
))))
31 ;;; the number of bytes in a word
32 (def!constant n-word-bytes
(/ n-word-bits n-byte-bits
))
34 ;;; the number of bits used in the header word of a data block to store
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
)))
40 (def!constant sb
!xc
:most-positive-fixnum
41 (1- (ash 1 (- n-word-bits n-lowtag-bits
)))
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
))
47 "the fixnum closest in value to negative infinity")