Programming Exercise (HP-15C, 15C LE - and others)

[Dave Britten]

Just for fun, here it is for the 20S, a (GASP!) algebraic model. Whenever I code for the 20S, I usually end up having to abuse its features/quirks in unusual ways, and this one is no different. It's been a couple years since I dug into it, though, so there's probably still room for improvement. This completed in just under 10.5 minutes, and yielded a result of 6.93097183E-1.

01- LBL A
02- CLRG
03- 1
04- STO 0
05- E
06- 4
07- STO 4 (Prepare the trickery)
08- LBL 0
09- x
10- RCL 0
11- +/-
12- STO 0
13- =
14- 1/x
15- STO+ 1
16- SIGMA- (Trickery)
17- x=0?
18- GTO 1
19- GTO 0
20- LBL 1
21- RCL 1
22- RTN

Basically, I'm banking on SIGMA- being faster than 1, +/-, RCL+ 4, STO 4. I haven't actually tested that hypothesis yet, mind you.