How do you calculate %xHKO?

I'm going to concede that my program doesn't calculate it correctly at the moment. Has a problem with not counting all the different ways a certain damage amount can occur (e.g., 42504 can occur 6 different ways). For the case above, I think it should give correct results due to a 50/50 scenario being symmetric... but being correct because of that is hardly satisfactory.
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Also, since I must (at some time) rewrite my program, I have a question.
Question: How exactly is damage calculated? More precisely, at what point in damage calculation does the game (randomly) choose a number?

 Spoiler

So I suppose there are a few possibilities.
a) The game uses your stats to calculate your range; then randomly chooses numbers from your range, then applies WDEF modification, critical/damage multipliers, rounds down (calculates damage).
b) Or does the game calculate the your min/max damage then randomly choose numbers from this range? (So this possibility is: calculate damage then randomly choose.)

c) For Assassin/Hermit/Night Lord, there is a separate range formula for Lucky 7/Triple Throw from that of Normal Attack, Drain, Avenger, etc. So there's a question here similar to a) and b) above.[INDENT]Does the game calculate this range for Lucky 7/Triple Throw and randomly choose a number from that?

Or does the game calculate the min/max damage possibility and choose randomly from this range?[/INDENT][INDENT] Or there can be a 3rd possibility for this case:
L7/TT Min: 2.5*LUK/100*ATT
L7/TT Max: 5.0*LUK/100*ATT
Does the game choose randomly between 2.5 and 5.0? And then do all the other calculations? (This 3rd possibility seems unlikely though...?)[/INDENT]

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So the reason it matters is because:
If the game calculates damage by a), then there are gaps in damage. Your min/max damage will be possibilities but not so for all the numbers in between. For example, damage possibilities might be like: 14167, 14169, 14170, 14172, etc.

And of course, this affects how I should write the calculation section.