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; -*- Mode: Scheme; Syntax: Scheme; Package: Scheme; -*-
; Part of Scheme 48 1.9. See file COPYING for notices and license.
; Authors: Richard Kelsey, Jonathan Rees, David Frese, Taylor Campbell
(define (address1+ x)
(address+ x addressing-units-per-cell))
(define (address2+ x)
(address1+ (address1+ x)))
; Memory access
(define *memory*)
(define *memory-begin* 0)
(define *memory-end* 0)
(define (memory-begin)
*memory-begin*)
; Size of memory in cells.
(define (memory-size)
(a-units->cells (address-difference *memory-end* *memory-begin*)))
(define (create-memory size initial-value) ;size in cells
(let ((size (cells->a-units size)))
(cond ((not (= size (address-difference *memory-end* *memory-begin*)))
(if (not (= *memory-end* 0))
(deallocate-memory *memory*))
(set! *memory* (allocate-memory size))
(if (null-address? *memory*)
(error "out of memory, unable to continue"))
(set! *memory-begin* *memory*)
(set! *memory-end* (+ *memory* size))))))
(define fetch word-ref)
(define fetch-byte unsigned-byte-ref)
(define fetch-flonum flonum-ref)
(define store! word-set!)
(define store-byte! unsigned-byte-set!)
(define store-flonum! flonum-set!)
(define fetch-string char-pointer->string)
(define fetch-nul-terminated-string char-pointer->nul-terminated-string)
;----------------------------------------------------------------
(define (address->stob-descriptor addr)
(add-stob-tag (address->integer addr)))
(define stob-overhead 1) ; header uses up one descriptor
(define (offset-after-header stob)
(assert (stob? stob))
(remove-stob-tag stob))
(define (address-after-header stob)
(integer->address (offset-after-header stob)))
; Note that first converting to an address and then doing arithmetic
; will result in C undefined behavior when the target address is NULL.
(define (address-at-header stob)
(integer->address (- (offset-after-header stob)
(cells->bytes 1))))
(define (stob-header stob)
(fetch (address-at-header stob)))
(define (stob-header-set! stob header)
(store! (address-at-header stob) header))
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