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racket/draw: fix race in setting up pre-multiply tables for bitmap ops

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This commit is contained in:
Matthew Flatt 2012-12-23 06:34:45 -07:00
parent 6f40e86037
commit 27a1121869
1 changed files with 26 additions and 24 deletions
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50
collects/racket/draw/private/bitmap.rkt
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@ -78,33 +78,35 @@
(define unmult-table #f)
(define (get-mult-table)
(unless mult-table
(set! mult-table (make-bytes (* 256 256)))
(for ([a (in-range 256)])
(for ([v (in-range 256)])
(bytes-set! mult-table
(fx+ (fx* a 256) v)
(unsafe-fl->fx
(unsafe-flround
(unsafe-fl/
(unsafe-fx->fl (fx* a v))
255.0)))))))
(atomically
(unless mult-table
(set! mult-table (make-bytes (* 256 256)))
(for ([a (in-range 256)])
(for ([v (in-range 256)])
(bytes-set! mult-table
(fx+ (fx* a 256) v)
(unsafe-fl->fx
(unsafe-flround
(unsafe-fl/
(unsafe-fx->fl (fx* a v))
255.0))))))))
mult-table)
(define (get-unmult-table)
(unless unmult-table
(set! unmult-table (make-bytes (* 256 256)))
(for ([a (in-range 256)])
(for ([v (in-range 256)])
(bytes-set! unmult-table
(fx+ (fx* a 256) v)
(if (unsafe-fx<= a v)
255
(unsafe-fl->fx
(unsafe-flround
(unsafe-fl/
(unsafe-fx->fl (fx* 255 v))
(unsafe-fx->fl a)))))))))
(atomically
(unless unmult-table
(set! unmult-table (make-bytes (* 256 256)))
(for ([a (in-range 256)])
(for ([v (in-range 256)])
(bytes-set! unmult-table
(fx+ (fx* a 256) v)
(if (unsafe-fx<= a v)
255
(unsafe-fl->fx
(unsafe-flround
(unsafe-fl/
(unsafe-fx->fl (fx* 255 v))
(unsafe-fx->fl a))))))))))
unmult-table)
(define (alpha-mult al v)