HP 50g Double factorial

[Giuseppe Donnini]

(05-01-2019 06:17 PM)Albert Chan Wrote:  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.

Thanks, Albert, for your valuable comments. Sure there is! Here we go:

\<<
  1 SWAP          @ Initialize result.
  WHILE
    DUP 2 \>=     @ Repeat while factor >= 2.
  REPEAT
    DUP ROT *     @ Multiply product with current factor.
    SWAP 2 -      @ Decrement factor by 2.
  END DROP        @ Drop remaining factor (by now invalid, i.e. < 2).
\>>

Saves 9 bytes, but negative arguments will return 1, too, whereas my former implementation left them unchanged.