HP 50g Double factorial

[Albert Chan]

(05-01-2019 05:05 PM)Giuseppe Donnini Wrote:  
1          @ Initialize result.
SWAP 2     @ Loop down from n to 2.
FOR f f *  @ Multiply with current factor.
-2 STEP    @ Decrement factor by 2 ; repeat until factor < 2.

Taking into account the special case where  n = 0 , we finally have ...

I am not familiar with RPL code, but is there a loop construct where you test the condition first ?
That way, the 0 special case need not be added.

BTW, I like your code. Doing odd n!! as n! / (n-1)!! might overflow the result.