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123 lines
5.6 KiB
Racket
123 lines
5.6 KiB
Racket
#lang debug racket/base
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(require "helper.rkt"
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"number.rkt"
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racket/dict
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racket/class
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racket/promise
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sugar/unstable/dict)
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(provide (all-defined-out))
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#|
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approximates
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https://github.com/mbutterick/restructure/blob/master/src/Pointer.coffee
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|#
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(define (find-top-parent parent)
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(cond
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[(dict-ref parent 'parent #f) => find-top-parent]
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[else parent]))
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(define (resolve-void-pointer type val)
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(cond
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[type (values type val)]
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[(xvoid-pointer? val) (values (xvoid-pointer-type val) (xvoid-pointer-value val))]
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[else (raise-argument-error 'Pointer:size "VoidPointer" val)]))
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(define xpointer%
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(class xenobase%
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(super-new)
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(init-field offset-type type options)
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(define pointer-relative-to (dict-ref options 'relative-to))
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(define allow-null (dict-ref options 'allowNull))
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(define null-value (dict-ref options 'nullValue))
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(define pointer-lazy? (dict-ref options 'lazy))
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(define/augment (xxdecode port parent)
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(define offset (send offset-type xxdecode port parent))
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(cond
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[(and allow-null (= offset null-value)) #f] ; handle null pointers
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[else
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(define relative (+ (case pointer-relative-to
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[(local) (dict-ref parent '_startOffset)]
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[(immediate) (- (pos port) (send offset-type xxsize))]
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[(parent) (dict-ref (dict-ref parent 'parent) '_startOffset)]
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[(global) (or (dict-ref (find-top-parent parent) '_startOffset) 0)]
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[else (error 'unknown-pointer-style)])))
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(define ptr (+ offset relative))
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(cond
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[type (define (decode-value)
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(define orig-pos (pos port))
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(pos port ptr)
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(begin0
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(send type xxdecode port parent)
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(pos port orig-pos)))
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(if pointer-lazy? (delay (decode-value)) (decode-value))]
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[else ptr])]))
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(define/augment (xxencode val port [parent #f])
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(unless parent ; todo: furnish default pointer context? adapt from Struct?
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(raise-argument-error 'xpointer-encode "valid pointer context" parent))
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(if (not val)
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(send offset-type xxencode null-value port)
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(let* ([new-parent (case pointer-relative-to
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[(local immediate) parent]
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[(parent) (dict-ref parent 'parent)]
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[(global) (find-top-parent parent)]
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[else (error 'unknown-pointer-style)])]
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[relative (+ (case pointer-relative-to
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[(local parent) (dict-ref new-parent 'startOffset)]
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[(immediate) (+ (pos port) (send offset-type xxsize val parent))]
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[(global) 0]))])
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(send offset-type xxencode (- (dict-ref new-parent 'pointerOffset) relative) port)
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(let-values ([(type val) (resolve-void-pointer type val)])
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(dict-set! new-parent 'pointers (append (dict-ref new-parent 'pointers)
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(list (mhasheq 'type type
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'val val
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'parent parent))))
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(dict-set! new-parent 'pointerOffset
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(+ (dict-ref new-parent 'pointerOffset) (send type xxsize val parent)))))))
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(define/augment (xxsize [val #f] [parent #f])
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(let*-values ([(parent) (case pointer-relative-to
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[(local immediate) parent]
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[(parent) (dict-ref parent 'parent)]
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[(global) (find-top-parent parent)]
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[else (error 'unknown-pointer-style)])]
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[(type val) (resolve-void-pointer type val)])
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(when (and val parent)
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(dict-set! parent 'pointerSize (and (dict-ref parent 'pointerSize #f)
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(+ (dict-ref parent 'pointerSize) (send type xxsize val parent)))))
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(send offset-type xxsize)))))
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(define (+xpointer [offset-arg #f] [type-arg #f]
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#:offset-type [offset-kwarg #f]
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#:type [type-kwarg #f]
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#:relative-to [relative-to 'local]
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#:lazy [lazy? #f]
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#:allow-null [allow-null? #t]
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#:null [null-value 0]
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#:subclass [class xpointer%])
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(define valid-pointer-relatives '(local immediate parent global))
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(unless (memq relative-to valid-pointer-relatives)
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(raise-argument-error '+xpointer (format "~v" valid-pointer-relatives) relative-to))
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(define options (mhasheq 'relative-to relative-to
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'lazy lazy?
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'allowNull allow-null?
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'nullValue null-value))
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(define type-in (or type-arg type-kwarg uint8))
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(new class
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[offset-type (or offset-arg offset-kwarg uint8)]
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[type (case type-in [(void) #f][else type-in])]
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[options options]))
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;; A pointer whose type is determined at decode time
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(define xvoid-pointer% (class xenobase%
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(super-new)
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(init-field type value)))
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(define (+xvoid-pointer . args) (apply make-object xvoid-pointer% args))
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(define (xvoid-pointer? x) (is-a? x xvoid-pointer%))
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(define (xvoid-pointer-type x) (get-field type x))
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(define (xvoid-pointer-value x) (get-field value x))
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