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52 lines
1.5 KiB
Racket
52 lines
1.5 KiB
Racket
#lang racket/base
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(provide (all-defined-out))
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(define-values (input-wire input-wire? input-wire-get)
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(make-impersonator-property 'input-wire))
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(define (make-input [max-length 16])
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(impersonate-procedure
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(let ([max-length max-length]
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[val 0])
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(case-lambda
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[() val]
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[(bit)
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(when (and bit (>= bit max-length))
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(raise-argument-error 'make-input (format "bit index too large for bit length ~a" max-length) bit))
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(if (bitwise-bit-set? val (or bit 0)) 1 0)]
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[(bit arg)
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(when (and bit (>= bit max-length))
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(raise-argument-error 'make-input (format "bit index too large for bit length ~a" max-length) bit))
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(when (and arg (> arg (expt 2 max-length)))
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(raise-argument-error 'make-input (format "value too large for bit length ~a" max-length) arg))
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(cond
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[(and bit arg) (set! val (bitwise-ior val (expt 2 bit)))]
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[else (set! val arg)])])) ;; aka (and arg (not bit))
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#f input-wire #t))
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(module+ test
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(require rackunit)
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(define in-wire (make-input))
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(define other (λ () (+ 2 2)))
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(check-true (input-wire? in-wire))
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(check-false (input-wire? other))
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(define x (make-input 4))
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(check-equal? (x) 0)
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(x #f 12)
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(check-equal? (x) 12)
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(x #f 0)
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(check-equal? (x) 0)
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(x 3 1)
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(check-equal? (x) 8)
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(x 2 1)
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(check-equal? (x) 12)
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(check-equal? (x 3) 1)
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(check-equal? (x 2) 1)
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(check-equal? (x 1) 0)
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(check-equal? (x 0) 0)
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(check-exn exn:fail? (λ () (x #f 32)))
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(check-exn exn:fail? (λ () (x 22 1)))
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)
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