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lazy pointers

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Matthew Butterick 7 years ago
parent af9d77dc98
commit dd82c98ef5
4 changed files with 48 additions and 31 deletions
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4
pitfall/restructure/helper.rkt
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@ -18,4 +18,6 @@
(- (bitwise-xor uint most-significant-bit-mask) most-significant-bit-mask))
(define (signed->unsigned sint bits)
(bitwise-and sint (arithmetic-shift 1 bits)))
(bitwise-and sint (arithmetic-shift 1 bits)))
(struct LazyThunk (proc) #:transparent)

11
pitfall/restructure/pointer-test.rkt
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@ -1,5 +1,5 @@
#lang restructure/racket
(require "pointer.rkt" "stream.rkt" "buffer.rkt" "base.rkt" "number.rkt" rackunit)
(require "pointer.rkt" "stream.rkt" "buffer.rkt" "base.rkt" "number.rkt" "struct.rkt" rackunit)
#|
approximates
@ -91,7 +91,7 @@ https://github.com/mbutterick/restructure/blob/master/test/Pointer.coffee
(check-equal? (send pointer decode stream (mhash '_startOffset 0)) 4))
; todo: skipped lazy pointers for now
; it 'should support decoding pointers lazily', ->
; stream = new DecodeStream new Buffer [1, 53]
; struct = new Struct
@ -101,7 +101,12 @@ https://github.com/mbutterick/restructure/blob/master/test/Pointer.coffee
; Object.getOwnPropertyDescriptor(res, 'ptr').get.should.be.a('function')
; Object.getOwnPropertyDescriptor(res, 'ptr').enumerable.should.equal(true)
; res.ptr.should.equal 53
;
(let ([stream (+DecodeStream (+Buffer '(1 53)))]
[struct (+Struct (dictify 'ptr (+Pointer uint8 uint8 (mhasheq 'lazy #t))))])
(define res (send struct decode stream))
(check-true (LazyThunk? (hash-ref (get-field kv res) 'ptr)))
(check-equal? (· res ptr) 53))

21
pitfall/restructure/pointer.rkt
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@ -1,4 +1,5 @@
#lang restructure/racket
(require racket/undefined)
(provide (all-defined-out))
#|
@ -38,12 +39,20 @@ https://github.com/mbutterick/restructure/blob/master/src/Pointer.coffee
[else (error 'unknown-pointer-style)])
(relative-getter-or-0 ctx)))
(define ptr (+ offset relative))
(cond ; omitted: lazy pointer implementation
[type (define orig-pos (· stream pos))
(send stream pos ptr)
(define val (send type decode stream ctx))
(send stream pos orig-pos)
val]
(cond
[type (define val undefined)
(define (decode-value)
(cond
[(not (eq? val undefined)) val]
[else
(define orig-pos (· stream pos))
(send stream pos ptr)
(set! val (send type decode stream ctx))
(send stream pos orig-pos)
val]))
(if lazy
(LazyThunk decode-value)
(decode-value))]
[else ptr])]))

43
pitfall/restructure/struct.rkt
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@ -11,19 +11,20 @@ https://github.com/mbutterick/restructure/blob/master/src/Struct.coffee
(define private-keys '(parent _startOffset _currentOffset _length))
(define (choose-dict d k)
(if (memq k private-keys)
(get-field pvt d)
(get-field kv d)))
(define dictable<%>
(interface* ()
([(generic-property gen:dict)
(generic-method-table gen:dict
(define (dict-set! d k v) (d:dict-set! (if (memq k private-keys)
(get-field pvt d)
(get-field kv d)) k v))
(define (dict-ref d k [thunk #f]) (d:dict-ref (if (memq k private-keys)
(get-field pvt d)
(get-field kv d)) k thunk))
(define (dict-remove! d k) (d:dict-remove! (if (memq k private-keys)
(get-field pvt d)
(get-field kv d)) k))
(define (dict-set! d k v) (d:dict-set! (choose-dict d k) k v))
(define (dict-ref d k [thunk #f])
(define res (d:dict-ref (choose-dict d k) k thunk))
(if (LazyThunk? res) ((LazyThunk-proc res)) res))
(define (dict-remove! d k) (d:dict-remove! (choose-dict d k) k))
;; public keys only
(define (dict-keys d) (d:dict-keys (get-field kv d))))]
[(generic-property gen:custom-write)
@ -93,7 +94,7 @@ https://github.com/mbutterick/restructure/blob/master/src/Struct.coffee
'pointerSize 0))
(+ (for/sum ([(key type) (in-dict fields)]
#:when val)
(send type size (ref val key) ctx))
(send type size (ref val key) ctx))
(if include-pointers (· ctx pointerSize) 0)))
(define/augride (encode stream val [parent #f])
@ -112,9 +113,9 @@ https://github.com/mbutterick/restructure/blob/master/src/Struct.coffee
(raise-argument-error 'Struct:encode
(format "dict that contains superset of Struct keys: ~a" (dict-keys fields)) (dict-keys val)))
(for ([(key type) (in-dict fields)])
(send type encode stream (ref val key) ctx))
(send type encode stream (ref val key) ctx))
(for ([ptr (in-list (· ctx pointers))])
(send (· ptr type) encode stream (· ptr val) (· ptr parent)))))
(send (· ptr type) encode stream (· ptr val) (· ptr parent)))))
(test-module
@ -124,15 +125,15 @@ https://github.com/mbutterick/restructure/blob/master/src/Struct.coffee
;; make random structs and make sure we can round trip
(for ([i (in-range 20)])
(define field-types (for/list ([i (in-range 40)])
(random-pick (list uint8 uint16be uint16le uint32be uint32le double))))
(define size-num-types (for/sum ([num-type (in-list field-types)])
(send num-type size)))
(define s (+Struct (for/list ([num-type (in-list field-types)])
(cons (gensym) num-type))))
(define bs (apply bytes (for/list ([i (in-range size-num-types)])
(random 256))))
(check-equal? (send s encode #f (send s decode bs)) bs)))
(define field-types (for/list ([i (in-range 40)])
(random-pick (list uint8 uint16be uint16le uint32be uint32le double))))
(define size-num-types (for/sum ([num-type (in-list field-types)])
(send num-type size)))
(define s (+Struct (for/list ([num-type (in-list field-types)])
(cons (gensym) num-type))))
(define bs (apply bytes (for/list ([i (in-range size-num-types)])
(random 256))))
(check-equal? (send s encode #f (send s decode bs)) bs)))

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