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