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#lang racket/base
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(require "helper.rkt" 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 (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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(define flag-hash (mhasheq))
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(define val (decode (xbitfield-type xb)))
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(for ([(flag i) (in-indexed (xbitfield-flags xb))]
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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 (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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(define bit-int (for/sum ([(flag i) (in-indexed (xbitfield-flags xb))]
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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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(encode (xbitfield-type xb) bit-int)
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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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(size (xbitfield-type xb)))
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(struct xbitfield (type flags) #:transparent
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#:methods gen:xenomorphic
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[(define decode xbitfield-decode)
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(define encode xbitfield-encode)
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(define size xbitfield-size)])
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(define (+xbitfield type [flags 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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(xbitfield type flags))
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(module+ test
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(require rackunit "number.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")) |