Tricky array related problem

I’ll try to break this down as simple as I can.

I got this array with 5 values in it. they change through a random function like so;
ActionScript Code:
[FONT=Courier New][LEFT][COLOR=#000000]var[/COLOR] tArr:[COLOR=#0000FF]Array[/COLOR] = [COLOR=#000000][[/COLOR][COLOR=#000080]0[/COLOR],[COLOR=#000080]1[/COLOR],[COLOR=#000080]2[/COLOR],[COLOR=#000080]3[/COLOR],[COLOR=#000080]4[/COLOR][COLOR=#000000]][/COLOR];

[COLOR=#000000]function[/COLOR] updateCOLOR=#000000[/COLOR][COLOR=#000000]{[/COLOR]
tArr[COLOR=#000000][[/COLOR]whichone[COLOR=#000000]][/COLOR] = [COLOR=#0000FF]Math[/COLOR].[COLOR=#0000FF]floor[/COLOR][COLOR=#000000]([/COLOR][COLOR=#0000FF]Math[/COLOR].[COLOR=#0000FF]random[/COLOR]COLOR=#000000[/COLOR] * [COLOR=#000080]6[/COLOR][COLOR=#000000])[/COLOR];
[COLOR=#000000]}[/COLOR];
[/LEFT]
[/FONT]

Now, the problem is… I dont want any dups. Any of those 5 values can be 1 to 6, but they need to be unique. I mean, this is no good:

[1,1,2,5,6,6]

How would I do that? bit stumped : )

… oh its worth noting that this is in a time-critical function so I dont really want to “loop until one comes up”