ah yes, the ol' "sum of N identically distributed uniform random variables" :P i've wrestled with this in the past, tried to find a generalized closed form approximation for the probability distribution function of XdY for any X and Y. needless to say, i concluded that resorting to summing $r(1, Y) over X iterations was by far the most sane approach to the problem! (see the Irwin-Hall Distribution)

and it's great to see you've avoided the use of regular expressions to locate XdY, it certainly exposes one to clever and more realistic coding techniques ;P realism aside, an example of an alternative to a while loop that can be used once you've identified X and Y is the following:

//tokenize 100 2d20 | echo -a $calc( [ $str(+$r(1, $2), $1) ] )

Champagne, you're well aware that enjoyment of any description is strictly forbidden in #mSL!