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44 lines
1.4 KiB
Racket
44 lines
1.4 KiB
Racket
#lang racket/base
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(require "racket.rkt")
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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-subclass Streamcoder (Bitfield type [flags empty])
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(unless (andmap (λ (f) (or (key? f) (not f))) flags)
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(raise-argument-error 'Bitfield "list of keys" flags))
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(define/augment (decode stream . _)
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(define flag-hash (mhasheq))
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(for* ([val (in-value (send type decode stream))]
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[(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 (size . _) (send type size))
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(define/augment (encode port flag-hash [ctx #f])
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(define bit-int (for/sum ([(flag i) (in-indexed flags)]
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#:when (and flag (ref flag-hash flag)))
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(arithmetic-shift 1 i)))
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(send type encode port bit-int))
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(define/override (get-class-name) 'Bitfield))
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(test-module
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(require "number.rkt")
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(define bfer (+Bitfield uint16be '(bold italic underline #f shadow condensed extended)))
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(define bf (send bfer decode #"\0\25"))
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(check-equal? (length (ref-keys bf)) 6) ; omits #f flag
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(check-true (ref bf 'bold))
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(check-true (ref bf 'underline))
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(check-true (ref bf 'shadow))
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(check-false (ref bf 'italic))
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(check-false (ref bf 'condensed))
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(check-false (ref bf 'extended))
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(check-equal? (encode bfer bf #f) #"\0\25")) |