guard against bad pre-mult ARGB

Closes PR 11572
2010-12-28 20:03:56 -07:00 · 2010-12-28 20:03:56 -07:00 · 0476ab4fc4
commit 0476ab4fc4
parent 1d89cfc9d7
1 changed files with 6 additions and 2 deletions
--- a/collects/racket/draw/private/bitmap.rkt
+++ b/collects/racket/draw/private/bitmap.rkt
@ -614,9 +614,13 @@
                           [a (bytes-ref data (+ ri A))]
                           [unmult (lambda (a v)
                                     (if use-alpha?
-                                         (if (zero? a)
+                                         (if (unsafe-fx= 0 a)
                                             255
-                                             (unsafe-fxquotient (fx* v 255) a))
+					     ;; `min' shouldn't be necessary, but it's
+					     ;; just in case the data is ill-formed
+                                             (unsafe-fxmin 255 (unsafe-fxquotient 
+								(unsafe-fx* v 255) 
+								a)))
                                         v))])
                      (when alpha-channel?
                        (bytes-set! bstr pi a))