ikarus/src/ikarus.fasl.ss

;;; FASL 
;;;
;;; A fasl object is a header followed by one or more objects followed by an
;;; end-of-fasl marker
;;;
;;; The header is the string "#@IK01"
;;; The end of fasl marker is "@"
;;;
;;; An object is either:
;;;   "N" : denoting the empty list
;;;   "T" : denoting #t
;;;   "F" : denoting #f
;;;   "E" : denoting the end of file object
;;;   "U" : denoting the unspecified value
;;;   "I" + 4-bytes : denoting a fixnum (in host byte order)
;;;   "C" + 1-byte : denoting a character
;;;   "P" + object1 + object2 : a pair
;;;   "V" + 4-bytes(n) + object ... : a vector of length n followed by n objects
;;;   "v" + 4-byte(n) + octet ... : a bytevector of length n followed by n octets
;;;   "S" + 4-bytes(n) + char ... : a string
;;;   "M" + symbol-name : a symbol
;;;   "G" + pretty-name + unique-name : a gensym
;;;   "R" + rtd-name + rtd-symbol + field-count + field-names
;;;   "{" + field-count + rtd + fields
;;;   ">" + 4-bytes(i) : mark the next object with index i
;;;   "<" + 4-bytes(i) : dereference the object marked with index i
;;;   "x" : denotes code
;;;   "T" : Thunk; followed by code.






(library (ikarus fasl read)
  (export fasl-read)
  (import (ikarus)
          (ikarus code-objects)
          (ikarus system $codes)
          (ikarus system $records))

  (define who 'fasl-read)
  (define (assert-eq? x y)
    (unless (eq? x y)
      (error who "Expected ~s, got ~s\n" y x)))
  (define (char->int x)
    (if (char? x)
        (char->integer x)
        (error who "unexpected eof inside a fasl object")))
  (define (read-fixnum p)
    (let ([c0 (char->int (read-char p))]
          [c1 (char->int (read-char p))]
          [c2 (char->int (read-char p))]
          [c3 (char->int (read-char p))])
      (cond
        [(fx<= c3 127)
         (fxlogor (fxlogor (fxsra c0 2) (fxsll c1 6))
                  (fxlogor (fxsll c2 14) (fxsll c3 22)))]
        [else
         (let ([c0 (fxlogand #xFF (fxlognot c0))]
               [c1 (fxlogand #xFF (fxlognot c1))]
               [c2 (fxlogand #xFF (fxlognot c2))]
               [c3 (fxlogand #xFF (fxlognot c3))])
           (fx- -1 
             (fxlogor (fxlogor (fxsra c0 2) 
                               (fxsll c1 6))
                      (fxlogor (fxsll c2 14) 
                               (fxsll c3 22)))))])))
  (define (read-int p)
    (let ([c0 (char->int (read-char p))]
          [c1 (char->int (read-char p))]
          [c2 (char->int (read-char p))]
          [c3 (char->int (read-char p))])
      (cond
        [(fx<= c3 127)
         (fxlogor (fxlogor c0 (fxsll c1 8))
                  (fxlogor (fxsll c2 16) (fxsll c3 24)))]
        [else
         (let ([c0 (fxlogand #xFF (fxlognot c0))]
               [c1 (fxlogand #xFF (fxlognot c1))]
               [c2 (fxlogand #xFF (fxlognot c2))]
               [c3 (fxlogand #xFF (fxlognot c3))])
           (fx- -1 
             (fxlogor (fxlogor c0 
                               (fxsll c1 8))
                      (fxlogor (fxsll c2 16) 
                               (fxsll c3 24)))))]))) 
  (define (do-read p)
    (define marks (make-vector 1 #f))
    (define (max x y)
      (if (fx> x y) x y))
    (define (put-mark m obj)
      (cond
        [(fx< m (vector-length marks))
         (when (vector-ref marks m)
           (error 'fasl-read "mark ~s set twice" m))
         (vector-set! marks m obj)]
        [else
         (let ([n (vector-length marks)])
           (let ([v (make-vector 
                      (max (fx* n 2) (fx+ m 1))
                      #f)])
             (let f ([i 0])
               (cond
                 [(fx= i n) 
                  (set! marks v)
                  (vector-set! marks m obj)]
                 [else
                  (vector-set! v i (vector-ref marks i))
                  (f (fxadd1 i))]))))]))
    (define (read) (read/mark #f))
    (define (read-code code-m clos-m)
      (let* ([code-size (read-int p)]
             [freevars (read-fixnum p)])
        (let ([code (make-code code-size freevars)])
          (when code-m (put-mark code-m code))
          (let f ([i 0])
            (unless (fx= i code-size)
              (code-set! code i (char->int (read-char p)))
              (f (fxadd1 i))))
          (cond
            [clos-m
             (let ([clos ($code->closure code)])
               (put-mark clos-m clos)
               (set-code-reloc-vector! code (read))
               code)]
            [else
             (set-code-reloc-vector! code (read))
             code]))))
    (define (read-thunk m)
      (let ([c (read-char p)])
        (case c
          [(#\x)
           (let ([code (read-code #f m)])
             (if m (vector-ref marks m) ($code->closure code)))]
          [(#\<) 
           (let ([cm (read-int p)])
             (unless (fx< cm (vector-length marks))
               (error who "invalid mark ~s\n" m))
             (let ([code (vector-ref marks cm)])
               (let ([proc ($code->closure code)])
                 (when m (put-mark m proc))
                 proc)))]
          [(#\>)
           (let ([cm (read-int p)])
             (assert-eq? (read-char p) #\x)
             (let ([code (read-code cm m)])
               (if m (vector-ref marks m) ($code->closure code))))]
          [else (error who "invalid code header ~s" c)])))
    (define (read/mark m)
      (define (nom)
        (when m (error who "unhandled mark")))
      (let ([h (read-char p)])
        (case h
          [(#\I) 
           (nom)
           (read-fixnum p)]
          [(#\P)
           (if m
               (let ([x (cons #f #f)])
                 (put-mark m x)
                 (set-car! x (read))
                 (set-cdr! x (read))
                 x)
               (let ([a (read)])
                 (cons a (read))))]
          [(#\N) '()]
          [(#\T) #t]
          [(#\F) #f]
          [(#\E) (eof-object)]
          [(#\U) (void)]
          [(#\S) ;;; string
           (let ([n (read-int p)])
             (let ([str (make-string n)])
               (let f ([i 0])
                 (unless (fx= i n)
                   (let ([c (read-char p)])
                     (string-set! str i c)
                     (f (fxadd1 i)))))
               (when m (put-mark m str))
               str))]
          [(#\M) ;;; symbol
           (let ([str (read)])
             (let ([sym (string->symbol str)])
               (when m (put-mark m sym))
               sym))]
          [(#\G)
           (let* ([pretty (read)]
                  [unique (read)])
             (foreign-call "ikrt_strings_to_gensym" pretty unique))]
          [(#\V) ;;; vector
           (let ([n (read-int p)])
             (let ([v (make-vector n)])
               (when m (put-mark m v))
               (let f ([i 0])
                 (unless (fx= i n)
                   (vector-set! v i (read))
                   (f (fxadd1 i))))
               v))]
          [(#\x) ;;; code
           (read-code m #f)]
          [(#\Q) ;;; thunk
           (read-thunk m)]
          [(#\R)
           (let* ([rtd-name (read)]
                  [rtd-symbol (read)]
                  [field-count (read-int p)])
             (let ([fields
                    (let f ([i 0])
                      (cond
                        [(fx= i field-count) '()]
                        [else 
                         (let ([a (read)])
                           (cons a (f (fxadd1 i))))]))])
               (let ([rtd (make-record-type 
                            rtd-name fields rtd-symbol)])
                 (when m (put-mark m rtd))
                 rtd)))]
          [(#\{)
           (let ([n (read-int p)])
             (let ([rtd (read)])
               (let ([x ($make-record rtd n)])
                 (when m (put-mark m x))
                 (let f ([i 0])
                   (unless (fx= i n)
                     (record-set! x i (read))
                     (f (fxadd1 i))))
                 x)))]
          [(#\C)
           (let ([c (read-char p)])
             (cond
               [(char? c) c]
               [else
                (error who "invalid eof inside a fasl object")]))]
          [(#\>)
           (let ([m (read-int p)])
             (read/mark m))]
          [(#\<)
           (let ([m (read-int p)])
             (unless (fx< m (vector-length marks))
               (error who "invalid mark ~s\n" m))
             (vector-ref marks m))]
          [else
           (error who "Unexpected ~s as a fasl object header" h)])))
    (read))
  (define $fasl-read
    (lambda (p)
      (assert-eq? (read-char p) #\I)
      (assert-eq? (read-char p) #\K)
      (assert-eq? (read-char p) #\0)
      (assert-eq? (read-char p) #\1)
      (do-read p)))
  
  (define fasl-read
    (case-lambda
      [() ($fasl-read (current-input-port))]
      [(p) 
       (if (input-port? p) 
           ($fasl-read p)
           (error 'fasl-read "~s is not an input port" p))]))

  )