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#lang racket/base
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(require "helper.rkt" racket/class racket/dict 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/Bitfield.coffee
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|#
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#;(define/post-decode (xbitfield-decode xb [port-arg (current-input-port)] #:parent [parent #f])
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(define port (->input-port port-arg))
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(parameterize ([current-input-port port])
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))
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#;(define/pre-encode (xbitfield-encode xb flag-hash [port-arg (current-output-port)] #:parent [parent #f])
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(define port (if (output-port? port-arg) port-arg (open-output-bytes)))
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(parameterize ([current-output-port port])
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(unless port-arg (get-output-bytes port))))
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#;(define (xbitfield-size xb [val #f] #:parent [parent #f])
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)
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#;(struct xbitfield xbase (type flags) #:transparent
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#:methods gen:xenomorphic
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[(define decode xbitfield-decode)
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(define xdecode xbitfield-decode)
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(define encode xbitfield-encode)
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(define size xbitfield-size)])
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(define xbitfield%
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(class xenobase%
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(super-new)
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(init-field type flags)
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(define flag-hash (mhasheq))
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(define/augment (xxdecode port parent)
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(define val (send type xxdecode port))
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(for ([(flag i) (in-indexed flags)]
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#:when flag)
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(hash-set! flag-hash flag (bitwise-bit-set? val i)))
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flag-hash)
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(define/augment (xxencode array port [parent #f])
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(define bit-int (for/sum ([(flag i) (in-indexed flags)]
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#:when (and flag (dict-ref flag-hash flag #f)))
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(arithmetic-shift 1 i)))
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(send type xxencode bit-int port))
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(define/augment (xxsize [val #f] [parent #f])
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(send type xxsize))))
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(define (+xbitfield [type-arg #f] [flag-arg #f]
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#:type [type-kwarg #f]
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#:flags [flag-kwarg #f]
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#:subclass [class xbitfield%])
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(define type (or type-arg type-kwarg))
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(define flags (or flag-arg flag-kwarg null))
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(unless (andmap (λ (f) (or (symbol? f) (not f))) flags)
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(raise-argument-error '+xbitfield "list of symbols" flags))
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(new class [type type] [flags flags]))
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(module+ test
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(require rackunit "number.rkt" "generic.rkt")
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(define bfer (+xbitfield uint16be '(bold italic underline #f shadow condensed extended)))
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(define bf (decode bfer #"\0\25"))
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(check-equal? (length (dict-keys bf)) 6) ; omits #f flag
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(check-true (dict-ref bf 'bold))
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(check-true (dict-ref bf 'underline))
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(check-true (dict-ref bf 'shadow))
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(check-false (dict-ref bf 'italic))
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(check-false (dict-ref bf 'condensed))
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(check-false (dict-ref bf 'extended))
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(check-equal? (encode bfer bf #f) #"\0\25")) |