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; Part of Scheme 48 1.9. See file COPYING for notices and license.
; Authors: Richard Kelsey, Jonathan Rees, Mike Sperber, Marcus Crestani
; Scheme 48's data representations, for writing heap images.
; Defines things needed by TRANSPORT (which is called by WRITE-IMAGE, which
; is called by the static linker).
; Adapted from vm/util/vm-utilities.scm and vm/data/data.scm.
(define (low-bits n k)
(bitwise-and n (- (arithmetic-shift 1 k) 1)))
(define (high-bits n k)
(arithmetic-shift n (- 0 k)))
(define (adjoin-bits high low width)
(bitwise-ior (arithmetic-shift high width) low))
; Data descriptions copied from DATA.SCM
(define-enumeration tag
(fixnum
immediate
header
stob))
(define-enumeration imm
(false ; #f
true ; #t
char
unspecific
undefined
eof
null))
(define bits-per-fixnum
(- (if (< bits-per-cell s48-useful-bits-per-word)
bits-per-cell
s48-useful-bits-per-word)
tag-field-width))
(define least-fixnum-value (- 0 (arithmetic-shift 1 (- bits-per-fixnum 1))))
(define greatest-fixnum-value (- (arithmetic-shift 1 (- bits-per-fixnum 1))
1))
(define (fixnum? x)
(and (integer? x)
(>= x least-fixnum-value)
(<= x greatest-fixnum-value)))
(define (immediate? x)
(or (fixnum? x)
(char? x)
(eq? x #t)
(eq? x '()) ; I think order is important here as () is a literal while
(eq? x #f) ; #F is generated with an instruction. If () = #f then
; we still lose on something like '(#F) (which is
; present in the system).
;; (eq? thing (unspecific))
))
(define car-offset 0)
(define cdr-offset 1)
(define closure-template-offset 0)
(define closure-env-offset 1)
(define location-id-offset 0)
; Procedures for manipulating bits
(define (make-descriptor tag data)
(adjoin-bits data tag tag-field-width))
(define (make-immediate type info)
(make-descriptor (enum tag immediate)
(adjoin-bits info type immediate-type-field-width)))
(define vm-true (make-immediate (enum imm true) 0))
(define vm-false (make-immediate (enum imm false) 0))
(define vm-null (make-immediate (enum imm null) 0))
(define vm-unspecific (make-immediate (enum imm unspecific) 0))
(define vm-unbound (make-immediate (enum imm undefined) 1))
(define vm-unassigned (make-immediate (enum imm undefined) 2))
(define header-type-field-width (- immediate-type-field-width 1))
(define (make-header type length-in-bytes)
(make-descriptor (enum tag header) (adjoin-bits length-in-bytes
type
(+ 1 header-type-field-width))))
(define (make-header-immutable header)
(bitwise-ior header (arithmetic-shift 1 (+ tag-field-width
header-type-field-width))))
(define (make-stob-descriptor addr)
(bitwise-ior (enum tag stob) addr))
(define (bytes->cells bytes)
(quotient (+ bytes (- bytes-per-cell 1))
bytes-per-cell))
(define (cells->bytes cells)
(* cells bytes-per-cell))
(define (cells->a-units cells)
(adjoin-bits cells 0 unused-field-width))
(define (a-units->cells cells)
(high-bits cells unused-field-width))
(define (bytes->a-units byte-count)
(cells->a-units (bytes->cells byte-count)))
;; Unicode code points
(define bytes-per-scalar-value-unit 4) ; must be >= 3
(define (bytes->scalar-value-units byte-count)
(quotient byte-count bytes-per-scalar-value-unit))
(define (scalar-value-units->bytes units)
(* units bytes-per-scalar-value-unit))
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