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early-vm.lisp    42 lines (37 with data), 1.7 kB

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;;;; 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")
;;; the number of bits at the low end of a pointer used for type
;;; information
(def!constant n-lowtag-bits
(integer-length (1- (/ (* 2 n-word-bits) n-byte-bits))))
;;; a mask to extract the low tag bits from a pointer
(def!constant lowtag-mask (1- (ash 1 n-lowtag-bits)))
;;; the exclusive upper bound on the value of the low tag bits from a
;;; pointer
(def!constant lowtag-limit (ash 1 n-lowtag-bits))
;;; the number of tag bits used for a fixnum
(def!constant n-fixnum-tag-bits (1- n-lowtag-bits))
;;; the fixnum tag mask
(def!constant fixnum-tag-mask (1- (ash 1 n-fixnum-tag-bits)))
;;; the bit width of positive fixnums
(def!constant n-positive-fixnum-bits (- n-word-bits n-fixnum-tag-bits 1))
;;; the number of bits used in the header word of a data block to store
;;; the type
(def!constant n-widetag-bits 8)
;;; a mask to extract the type from a data block header word
(def!constant widetag-mask (1- (ash 1 n-widetag-bits)))
(def!constant sb!xc:most-positive-fixnum
(1- (ash 1 (- n-word-bits n-lowtag-bits)))
#!+sb-doc
"the fixnum closest in value to positive infinity")
(def!constant sb!xc:most-negative-fixnum
(ash -1 (- n-word-bits n-lowtag-bits))
#!+sb-doc
"the fixnum closest in value to negative infinity")