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#lang racket/base
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(require "base.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 x:bitfield%
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(class xenobase%
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(super-new)
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(init-field [(@type type)][(@flags flags)])
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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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(define/augment (:decode port parent)
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(define val (send @type :decode port))
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(define flag-hash (mhasheq))
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(for ([(flag idx) (in-indexed @flags)]
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#:when flag)
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(hash-set! flag-hash flag (bitwise-bit-set? val idx)))
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flag-hash)
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(define/augment (:encode flag-hash port [parent #f])
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(define bit-int (for/sum ([(flag idx) (in-indexed @flags)]
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#:when (and flag (hash-ref flag-hash flag #f)))
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(arithmetic-shift 1 idx)))
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(send @type :encode bit-int port))
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(define/augment (:size [val #f] [parent #f])
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(send @type :size))))
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(define (x:bitfield [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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#:pre-encode [pre-proc #f]
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#:post-decode [post-proc #f])
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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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(new (generate-subclass x:bitfield% pre-proc post-proc) [type type] [flags flags]))
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(module+ test
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(require rackunit "number.rkt" "base.rkt")
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(define bfer (x:bitfield 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 (hash-keys bf)) 6) ; omits #f flag
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(check-true (hash-ref bf 'bold))
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(check-true (hash-ref bf 'underline))
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(check-true (hash-ref bf 'shadow))
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(check-false (hash-ref bf 'italic))
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(check-false (hash-ref bf 'condensed))
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(check-false (hash-ref bf 'extended))
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(check-equal? (encode bfer bf #f) #"\0\25")) |