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typesetting/pitfall/binparser/gif-parse.rkt

37 lines
1.8 KiB
Racket

#lang br
(require pitfall/binprint binparser)
;; http://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp
(define-rule gif (:seq [signature (:bytes 3 #:type string/ascii?)]
[version (:bytes 3 #:type string/ascii?)]
logical-screen-descriptor
#:type hash?))
(define-rule logical-screen-descriptor (:seq [width (:bytes 2 #:type integer?)]
[height (:bytes 2 #:type integer?)]
[lsd-flags (:bitfield [reserved (:bits 3)]
[disposal (:bits 3 #:type integer?)]
[user-input (:bits 1 #:type boolean?)]
[transparent (:bits 1 #:type boolean?)]
#:type hash?)]
[bgcolor-idx (:bytes 1 #:type integer?)]
[aspect (:bytes 1 #:type integer?)]
#:type hash?))
(gif (open-input-file "test.gif"))
(check-equal? (gif (gif (open-input-file "test.gif"))) (read-bytes 13 (open-input-file "test.gif")))
(require rackunit)
#;(check-equal? (parse-with-template "test.gif" gif)
(cons 'gif
(make-hasheq (list (cons 'logical-screen-descriptor '(162 162 (#f #t #f #f #f #t #f #t) 0 0))
'(signature . "GIF")
'(version . "87a")))))
(define-rule bad-bitfield (:bitfield [reserved (:bits 3)]
[disposal (:bits 3 #:type integer?)]))
(bad-bitfield (bad-bitfield (open-input-bytes #"A")))