scsh-0.6/scheme/vm/struct.scm

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1999-09-14 08:45:02 -04:00
; -*- Mode: Scheme; Syntax: Scheme; Package: Scheme; -*-
; Copyright (c) 1993-1999 by Richard Kelsey and Jonathan Rees. See file COPYING.
; This is file struct.scm.
; This file defines a level of abstraction for storage somewhat higher
; than that of d-vectors and b-vectors: pairs, symbols, and other datatypes.
(define (stob-maker type maker)
(lambda (length key)
(maker type length key)))
(define (stob-predicate type)
(lambda (obj) (stob-of-type? obj type)))
; data for these comes from STOB-DATA in arch.scm
(define-shared-primitive-data-type pair #t)
(define-shared-primitive-data-type symbol #t #f
make-symbol ; hidden from RTS
()
(symbol-next set-symbol-next!)) ; hidden from RTS
(define-shared-primitive-data-type closure #f #t)
(define-shared-primitive-data-type location)
(define-shared-primitive-data-type weak-pointer)
(define-shared-primitive-data-type shared-binding #f #f
#f
()
(shared-binding-next set-shared-binding-next!)) ; hidden from RTS
(define-shared-primitive-data-type port)
(define-shared-primitive-data-type channel #f #f
make-channel ; hidden from RTS
(;; these setters are hidden from the RTS
(channel-status set-channel-status!)
(channel-id set-channel-id!)
(channel-os-index set-channel-os-index!))
;; none of these are visible to the RTS
(channel-next set-channel-next!)
(channel-os-status set-channel-os-status!))
; Vectors and so on
(define-vector-data-type vector #t)
(define-vector-data-type record)
(define-vector-data-type extended-number)
(define-vector-data-type continuation)
(define-vector-data-type template)
(define (vm-vector-fill! v val)
(do ((i 0 (+ i 1)))
((= i (vm-vector-length v)) v)
(vm-vector-set! v i val)))
(define (continuation-cont c) (continuation-ref c 0))
(define (continuation-pc c) (continuation-ref c 1))
(define (continuation-template c) (continuation-ref c 2))
(define (continuation-env c) (continuation-ref c 3))
; Continuations are only initialized
(define (set-continuation-cont! c val) (d-vector-init! c 0 val))
(define (set-continuation-pc! c val) (d-vector-init! c 1 val))
(define (set-continuation-template! c val) (d-vector-init! c 2 val))
(define (set-continuation-env! c val) (d-vector-init! c 3 val))
(define continuation-cells 4)
(define (template-code tem) (template-ref tem 0))
(define (template-name tem) (template-ref tem 1))
; The VM needs a few templates for various obscure purposes.
(define (make-template-containing-ops op1 op2 key)
(let ((temp (make-template 2 key))
(code (make-code-vector 2 key)))
(template-set! temp 0 code)
(code-vector-set! code 0 op1)
(code-vector-set! code 1 op2)
temp))
(define (op-template-size op-count)
(+ (template-size 2) (code-vector-size op-count)))
; Code vectors
(define make-code-vector (stob-maker (enum stob byte-vector) make-b-vector))
(define code-vector? (stob-predicate (enum stob byte-vector)))
(define code-vector-length b-vector-length)
(define code-vector-ref b-vector-ref)
(define code-vector-set! b-vector-set!)
(define (code-vector-size len)
(+ stob-overhead (bytes->cells len)))
; Strings are presented as being one character shorter than they really
; are to hide the null character at the end.
(define (vm-make-string length key)
(let ((string (make-b-vector (enum stob string) (+ length 1) key)))
(b-vector-set! string length 0)
string))
(define vm-string? (stob-predicate (enum stob string)))
(define vm-string-length (lambda (x) (- (b-vector-length x) 1)))
(define vm-string-ref (lambda (s i) (ascii->char (b-vector-ref s i))))
(define vm-string-set! (lambda (s i c) (b-vector-set! s i (char->ascii c))))
(define (vm-string-size length)
(+ stob-overhead (bytes->cells (+ 1 length))))
(define (enter-string string key) ; used by VMIO on startup
(let ((z (string-length string)))
(let ((v (vm-make-string z key)))
(do ((i 0 (+ i 1)))
((>= i z) v)
(vm-string-set! v i (string-ref string i))))))
; This depends on our having 0 bytes at the end of strings.
(define (extract-string string) ; used by OPEN
(fetch-nul-terminated-string (address-after-header string)))
(define (vm-string=? s1 s2)
(assert (and (vm-string? s1) (vm-string? s2)))
(let ((len (b-vector-length s1)))
(and (= len (b-vector-length s2))
(memory-equal? (address-after-header s1)
(address-after-header s2)
len))))
; Number predicates
(define bignum? (stob-predicate (enum stob bignum)))
(define ratnum? (stob-predicate (enum stob ratnum)))
(define double? (stob-predicate (enum stob double)))
; Hashing
; The hash function used here is to take the sum of the ascii values
; of the characters in the string, modulo the symbol table size.
;
; This hash function was also compared against some others, e.g.
; adding in the length as well, and taking only the odd or only the
; even characters. It fared about the same as adding the length, and
; much better than examining only every other character.
;
; Perhaps a hash function that is sensitive to the positions of the
; characters should be tried? (Consider CADDR, CDADR, CDDAR.)
;
; Of course, if we switched to rehashing, a prime modulus would be
; important.
(define (vm-string-hash s)
(let ((n (vm-string-length s)))
(do ((i 0 (+ i 1))
(h 0 (+ h (char->ascii (vm-string-ref s i)))))
((>= i n) h))))