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78 lines
2.8 KiB
Racket
78 lines
2.8 KiB
Racket
#lang racket/base
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(require "racket.rkt")
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(require "utils.rkt" "array.rkt" "number.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/LazyArray.coffee
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|#
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(define (get o i) (send o get i))
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(define (LazyArray->list o) (send o to-list))
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(define-subclass object% (InnerLazyArray type [len #f] [port-in #f] [ctx #f])
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(field ([port port] (cond
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[(bytes? port-in) (open-input-bytes port-in)]
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[(port? port-in) port-in]
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[else (raise-argument-error 'LazyArray "port" port)])))
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(define starting-pos (pos port))
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(define item-cache (mhasheqv)) ; integer-keyed hash, rather than list
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(define/public-final (get index)
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(unless (<= 0 index (sub1 len))
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(raise-argument-error 'LazyArray:get (format "index in range 0 to ~a" (sub1 len)) index))
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(ref! item-cache index (λ ()
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(define orig-pos (pos port))
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(pos port (+ starting-pos (* (send type size #f ctx) index)))
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(define new-item (send type decode port ctx))
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(pos port orig-pos)
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new-item)))
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(define/public-final (to-list)
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(for/list ([i (in-range len)])
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(get i))))
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(define-subclass ArrayT (LazyArray)
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(inherit-field len type)
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(define/override (decode port [parent #f])
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(define starting-pos (pos port)) ; ! placement matters. `resolve-length` will change `pos`
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(define decoded-len (resolve-length len port parent))
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(let ([parent (if (NumberT? len)
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(mhasheq 'parent parent
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'_startOffset starting-pos
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'_currentOffset 0
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'_length len)
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parent)])
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(define res (+InnerLazyArray type decoded-len port parent))
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(pos port (+ (pos port) (* decoded-len (send type size #f parent))))
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res))
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(define/override (size [val #f] [ctx #f])
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(super size (if (InnerLazyArray? val)
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(send val to-list)
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val) ctx))
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(define/override (encode port val [ctx #f])
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(super encode port (if (InnerLazyArray? val)
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(send val to-list)
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val) ctx)))
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(test-module
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(define bstr #"ABCD1234")
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(define ds (open-input-bytes bstr))
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(define la (+LazyArray uint8 4))
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(define ila (decode la ds))
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(check-equal? (pos ds) 4)
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(check-equal? (get ila 1) 66)
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(check-equal? (get ila 3) 68)
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(check-equal? (pos ds) 4)
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(check-equal? (LazyArray->list ila) '(65 66 67 68))
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(define la2 (+LazyArray int16be (λ (t) 4)))
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(check-equal? (encode la2 '(1 2 3 4) #f) #"\0\1\0\2\0\3\0\4")
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(check-equal? (send (decode la2 (open-input-bytes #"\0\1\0\2\0\3\0\4")) to-list) '(1 2 3 4)))
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