scsh-0.6/scheme/prescheme/memory2.scm

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1999-09-14 08:45:02 -04:00
; Copyright (c) 1993-1999 by Richard Kelsey and Jonathan Rees. See file COPYING.
; An implementation of Pre-Scheme's memory interface that can detect some
; stray reads and writes. It has numerous limitiations:
; Allocations are always on page boundaries.
; No more than 16 megabytes can be allocated at once.
; More than 32 or 64 or so allocations result in addresses being
; bignums (dealloctions have no effect on this).
;
; Memory is represented as a vector of byte-vectors, with each byte-vector
; representing a 16-megabyte page. Allocations are always made on page
; boundaries, so the byte-vectors only need be as large as the allocated
; areas. Pages are never re-used.
; Memory is one big vector, with markers at beginning and end of free blocks
; and allocationg by by address ordered first fit.
; Strings and things end up as bignums...
(define *memory* (make-vector 0 0))
(define-record-type address :address
(make-address index)
address?
(index address-index))
(define-record-discloser :address
(lambda (addr) (list 'address (address-index addr))))
; We add 100000000 to addresses to make them
(define address-offset 100000000)
(define (address->integer addr)
(+ (address-index addr) address-offset))
(define (integer->address int)
(make-address (- int address-offset)))
(define (word-ref addr)
(if (address? addr)
(let ((index (address-index addr)))
(if (and (= 0
(vector-ref *memory* (address-index addr)))
(define (word-ref addr)
(vector-ref *memory* (address-index addr)))
(define *memory* (make-vector 16 #f)) ; vector of pages
(define log-max-size 24) ; log of page size
(define address-shift (- log-max-size)) ; turns addresses into page indices
(define max-size (arithmetic-shift 1 log-max-size)) ; page size
(define address-mask ; mask to get address within page
(- (arithmetic-shift 1 log-max-size) 1))
(define *next-index* 0) ; next available page
(define (reinitialize-memory)
(set! *memory* (make-vector 16 #f))
(set! *next-index* 0))
; Extend the page vector if necessary, and then make a page of the
; appropriate size.
(define (allocate-memory size)
(cond ((> size max-size)
#f) ; the null pointer
(else
(if (>= *next-index* (vector-length *memory*))
(let ((new (make-vector (* 2 (vector-length *memory*)))))
(do ((i 0 (+ i 1)))
((>= i (vector-length *memory*)))
(vector-set! new i (vector-ref *memory* i)))
(set! *memory* new)))
(let ((index *next-index*))
(set! *next-index* (+ *next-index* 1))
(vector-set! *memory* index (make-code-vector size 0))
(arithmetic-shift index log-max-size)))))
; Turning an address into a page or page index
(define (address->vector address)
(vector-ref *memory* (arithmetic-shift address address-shift)))
(define (address->vector-index address)
(bitwise-and address address-mask))
; Throw away the page containing ADDRESS, which must be the first address in
; that page,
(define (deallocate-memory address)
(let ((vector (address->vector address))
(byte-address (address->vector-index address)))
(if (and vector (= byte-address 0))
(vector-set! *memory* (arithmetic-shift address address-shift) #f)
(error "bad deallocation address" address))))
; Various ways of accessing memory
(define (unsigned-byte-ref address)
(code-vector-ref (address->vector address)
(address->vector-index address)))
(define (signed-code-vector-ref bvec i)
(let ((x (code-vector-ref bvec i)))
(if (< x 128)
x
(bitwise-ior x -128))))
(define (word-ref address)
(let ((vector (address->vector address))
(byte-address (address->vector-index address)))
(if (not (= 0 (bitwise-and byte-address 3)))
(error "unaligned address error" address)
(+ (+ (arithmetic-shift (signed-code-vector-ref vector byte-address) 24)
(arithmetic-shift (code-vector-ref vector (+ byte-address 1)) 16))
(+ (arithmetic-shift (code-vector-ref vector (+ byte-address 2)) 8)
(code-vector-ref vector (+ byte-address 3)))))))
(define (unsigned-byte-set! address value)
(code-vector-set! (address->vector address)
(address->vector-index address)
(bitwise-and 255 value)))
(define (word-set! address value)
(let ((vector (address->vector address))
(byte-address (address->vector-index address)))
(if (not (= 0 (bitwise-and byte-address 3)))
(error "unaligned address error" address))
(code-vector-set! vector byte-address
(bitwise-and 255 (arithmetic-shift value -24)))
(code-vector-set! vector (+ byte-address 1)
(bitwise-and 255 (arithmetic-shift value -16)))
(code-vector-set! vector (+ byte-address 2)
(bitwise-and 255 (arithmetic-shift value -8)))
(code-vector-set! vector (+ byte-address 3)
(bitwise-and 255 value))))
; Block I/O procedures.
(define (write-block port address count)
(let ((vector (address->vector address))
(byte-address (address->vector-index address)))
(do ((i 0 (+ i 1)))
((>= i count))
(write-char (ascii->char (code-vector-ref vector (+ i byte-address)))
port))
(values count (enum errors no-errors))))
(define (read-block port address count)
(cond ((not (char-ready? port))
(values 0 #f (enum errors no-errors)))
((eof-object? (s-peek-char port))
(values 0 #t (enum errors no-errors)))
(else
(let ((vector (address->vector address))
(byte-address (address->vector-index address)))
(let loop ((i 0))
(if (or (= i count)
(not (char-ready? port)))
(values i #f (enum errors no-errors))
(let ((c (s-read-char port)))
(cond ((eof-object? c)
(values i #f (enum errors no-errors)))
(else
(code-vector-set! vector
(+ i byte-address)
(char->ascii c))
(loop (+ i 1)))))))))))
(define (copy-memory! from to count)
(let ((from-vector (address->vector from))
(from-address (address->vector-index from))
(to-vector (address->vector to))
(to-address (address->vector-index to)))
(do ((i 0 (+ i 1)))
((>= i count))
(code-vector-set! to-vector
(+ i to-address)
(code-vector-ref from-vector
(+ i from-address))))))
(define (memory-equal? from to count)
(let ((from-vector (address->vector from))
(from-address (address->vector-index from))
(to-vector (address->vector to))
(to-address (address->vector-index to)))
(let loop ((i 0))
(cond ((>= i count)
#t)
((= (code-vector-ref to-vector (+ i to-address))
(code-vector-ref from-vector (+ i from-address)))
(loop (+ i 1)))
(else
#f)))))
; Turn the LENGTH bytes starting from ADDRESS into a string.
(define (char-pointer->string address length)
(let ((vector (address->vector address))
(byte-address (address->vector-index address))
(string (make-string length)))
(do ((i 0 (+ i 1)))
((= i length))
(string-set! string
i
(ascii->char (code-vector-ref vector (+ byte-address i)))))
string))
; Turn the bytes from ADDRESS to the next nul (byte equal to 0) into a
; string. This is a trivial operation in C.
(define (char-pointer->nul-terminated-string address)
(let ((vector (address->vector address))
(byte-address (address->vector-index address)))
(char-pointer->string address (index-of-first-nul vector byte-address))))
(define (index-of-first-nul vector address)
(let loop ((i address))
(cond ((= i (code-vector-length vector))
(error "CHAR-POINTER->STRING called on pointer with no nul termination"))
((= 0 (code-vector-ref vector i))
(- i address))
(else
(loop (+ i 1))))))
; We really need these to work.
(define address+ +)
(define address- -)
(define address-difference -)
(define address->integer identity)
(define integer->address identity)
(define ...)