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39 lines
1.7 KiB
Racket
39 lines
1.7 KiB
Racket
#lang restructure/racket
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(provide (all-defined-out))
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#| approximates
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https://github.com/mbutterick/restructure/blob/master/src/DecodeStream.coffee
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|#
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(define (read-bytes-exact count p)
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(define bs (read-bytes count p))
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(unless (and (bytes? bs) (= (bytes-length bs) count))
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(raise-argument-error 'read-bytes-exact (format "byte string length ~a" count) bs))
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bs)
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(provide (rename-out [type-sizes TYPES]))
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(define type-sizes (let-values ([(intkeys intvalues)
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(for*/lists (intkeys intvalues)
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([signed (in-list '(U ""))]
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[size (in-list '(8 16 24 32))])
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(values
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(format "~aInt~a" signed size)
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(/ size 8)))])
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(for/hash ([key (in-list (append '(Float Double) intkeys))]
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[value (in-list (append '(4 8) intvalues))]
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#:when key
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[endian '("" BE LE)])
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(values (string->symbol (format "~a~a" key endian)) value))))
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;; basically just a wrapper for a Racket port
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;; but needs to start with a buffer so length can be found
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(define-subclass object% (RDecodeStream [buffer #""])
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(field [_port (if (bytes? buffer)
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(open-input-bytes buffer)
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(raise-argument-error 'RDecodeStream "bytes" buffer))])
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(getter-field [pos (port-position _port)])
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(getter-field [length (bytes-length buffer)])
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(define/public (read count)
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(read-bytes-exact count _port))) |