Randomization a few used values with dist

[ryz]

Is there any good way of doing an distributed randomization with dist for a few values that I know will be used and a lot of other values that could be good to test.

I have a field that can take the value 0-511 where the values 63, 127, 255 and 511 will be used in the product but the other values should work. I therefore want to specify that the values 63, 127, 255 and 511 should be generated much more often then other values. What I have come up with is.

1)

top_seg_cfg_length dist {
    63:=4,
    127:=4,
    255:=4,
    511:=4,
    [0:62]    :/ 1,
    [64:126]  :/ 1,
    [128:254] :/ 1,
    [256:510] :/ 1
    };

which I think is ugly and a lot of unnecessary code. What I really would like to specify is

2)

top_seg_cfg_length dist {
    63:=4,
    127:=4,
    255:=4,
    511:=4,
    others    :/ 1,
    };

What will be the result if I would write

3)

top_seg_cfg_length dist {
    63:=4,
    127:=4,
    255:=4,
    511:=4,
    [0:511]   :/ 1,
    };

[dave_59]

You should use 3).

Then the weight of 63, 127, 255, and 511 will be (4 + (1/512))/17= 0.2354. The weight of 'others' will be (1/512)/17 = 1/8704 = 0.0001

[ryz]

3) should of course have been

top_seg_cfg_length dist {

63:=1,

127:=1,

255:=1,

511:=1,

[0:511] :/ 1,

};

to much copy and paste.

The problem with this is that other constrains can affect the distribution quite a lot. lets say we have the constrain

x dist {[0:3]:=1, [0:511]\=1} and then in some test case adds the constrains x < 5; That will boost the probability for [0:3] quite a lot. This would not be a problem with an others clause. In my case this is not a problem and I might never have any problem with it but it is something you have to keep in mind.