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#lang racket/base
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(require "base.rkt"
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"int.rkt"
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racket/class
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racket/dict
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racket/list
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racket/contract
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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/Bitfield.coffee
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|#
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(define x:bitfield%
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(class x:base%
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(super-new)
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(init-field [(@type type)]
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[(@flags flags)])
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(let ([named-flags (filter values @flags)])
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(unless (= (length named-flags) (length (remove-duplicates named-flags)))
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(raise-argument-error 'x:bitfield% "no duplicates among flag names" named-flags)))
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(when (> (length @flags) (* 8 (send @type x:size)))
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(raise-argument-error 'x:bitfield% (format "~a flags or fewer (~a-byte bitfield)" (* 8 (send @type x:size)) (send @type x:size)) (length @flags)))
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(define/augment (x:decode port parent)
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(define val (send @type x:decode port))
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(define flag-hash (mhash))
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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 (x:encode flag-hash port [parent #f])
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(define invalid-flags
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(for/list ([flag (in-hash-keys flag-hash)]
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#:unless (member flag @flags))
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flag))
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(unless (null? invalid-flags)
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(raise-argument-error 'encode (format "valid flag name ~v" @flags) invalid-flags))
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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 x:encode bit-int port))
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(define/augment (x:size [val #f] [parent #f])
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(send @type x:size))))
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(define (x:bitfield? x) (is-a? x x:bitfield%))
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(define/contract (x:bitfield
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[type-arg #f]
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[flag-arg #f]
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#:type [type-kwarg uint8]
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#:flags [flag-kwarg null]
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#:pre-encode [pre-proc #f]
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#:post-decode [post-proc #f]
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#:base-class [base-class x:bitfield%])
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(()
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((or/c x:int? #false)
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(listof any/c)
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#:type (or/c x:int? #false)
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#:flags (listof any/c)
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#:pre-encode (or/c (any/c . -> . any/c) #false)
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#:post-decode (or/c (any/c . -> . any/c) #false)
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#:base-class (λ (c) (subclass? c x:bitfield%)))
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. ->* .
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x:bitfield?)
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(define type (or type-arg type-kwarg))
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(define flags (or flag-arg flag-kwarg))
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(new (generate-subclass base-class pre-proc post-proc)
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[type type]
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[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")) |