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43 lines
1.4 KiB
Racket
43 lines
1.4 KiB
Racket
#lang restructure/racket
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(require "stream.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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(define/augment (decode stream . args)
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(for*/fold ([flag-hash (mhash)])
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([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/override (size . args) (send type size))
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(define/augment (encode stream flag-hash [ctx #f])
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(define bitfield-int (for/sum ([(flag i) (in-indexed flags)]
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#:when (and flag (hash-ref flag-hash flag)))
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(expt 2 i)))
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(send type encode stream bitfield-int)))
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(test-module
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(require "number.rkt" "stream.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 (+DecodeStream #"\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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(define os (+EncodeStream))
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(send bfer encode os bf)
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(check-equal? (send os dump) #"\0\25")) |