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#lang reader (submod "racket.rkt" reader)
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(require "number.rkt" "utils.rkt" "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/Array.coffee
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|#
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(define-subclass Streamcoder (ArrayT type [len #f] [length-type 'count])
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(define/augride (decode stream [parent #f])
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(define ctx (if (NumberT? len)
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(mhasheq 'parent parent
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'_startOffset (· stream pos)
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'_currentOffset 0
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'_length len)
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parent))
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(define decoded-len (resolve-length len stream parent))
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(cond
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[(or (not decoded-len) (eq? length-type 'bytes))
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(define end-pos (cond
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;; decoded-len is byte length
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[decoded-len (+ (· stream pos) decoded-len)]
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;; no decoded-len, but parent has length
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[(and parent (not (zero? (· parent _length)))) (+ (· parent _startOffset) (· parent _length))]
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;; no decoded-len or parent, so consume whole stream
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[else (· stream length_)]))
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(for/list ([i (in-naturals)]
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#:break (= (· stream pos) end-pos))
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(send type decode stream ctx))]
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;; we have decoded-len, which is treated as count of items
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[else (for/list ([i (in-range decoded-len)])
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(send type decode stream ctx))]))
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(define/augride (size [val #f] [ctx #f])
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(when val (unless (countable? val)
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(raise-argument-error 'Array:size "list or countable" val)))
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(cond
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[val (let-values ([(ctx len-size) (if (NumberT? len)
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(values (mhasheq 'parent ctx) (send len size))
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(values ctx 0))])
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(+ len-size (for/sum ([item (in-list (countable->list val))])
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(send type size item ctx))))]
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[else (let ([item-count (resolve-length len #f ctx)]
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[item-size (send type size #f ctx)])
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(* item-size item-count))]))
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(define/augride (encode port array [parent #f])
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(when array (unless (countable? array)
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(raise-argument-error 'Array:encode "list or countable" array)))
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(define (encode-items ctx)
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(define results (for/list ([item (in-list (countable->list array))])
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(send type encode port item ctx)))
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(unless port (apply bytes-append results)))
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(cond
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[(NumberT? len) (define ctx (mhash 'pointers null
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'startOffset (· port pos)
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'parent parent))
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(ref-set! ctx 'pointerOffset (+ (· port pos) (size array ctx)))
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(send len encode port (length array)) ; encode length at front
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(encode-items ctx)
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(for ([ptr (in-list (· ctx pointers))]) ; encode pointer data at end
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(send (· ptr type) encode port (· ptr val)))]
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[else (encode-items parent)])))
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(define-values (Array Array? +Array) (values ArrayT ArrayT? +ArrayT))
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(test-module
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(define A (+Array uint16be 3))
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(check-equal? (decode A #"ABCDEFG") '(16706 17220 17734))
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(check-equal? (encode A '(16706 17220 17734) #f) #"ABCDEF")
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(check-equal? (size (+Array uint16be) '(1 2 3)) 6)
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(check-equal? (size (+Array doublebe) '(1 2 3 4 5)) 40))
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