Example Program to calculate Factorial

[Thomas Okken]

(02-02-2018 06:59 PM)Dieter Wrote:  

(02-02-2018 03:28 PM)Gene Wrote:  A real shame HP kept flipping the included conditional tests back and forth back then. A real pain and one of the real cross-model design failures IMO.

That's something I never understood. Was ROM space or the number of available opcodes really so limited that the full set of 12 test commands could not be realized? In the late Seventies the standard set had only eight of them. But while x<0? exists there is no x<y?, and while there is an x≤y? the corresponding x≤0? is missing. Eventually the 41C then featured ten tests, but it still lacked the two for "greater or equal". Weird.

If there really was room for only eight tests HP better had chosen <, >, = and ≠. From these the missing ≤ and ≥ tests can easily be synthesized: the combination x≠y? x>y? is logically the same as x≥y?.

ROM space was definitely limited. The HP-25 ROM is full to the last byte. This is also the first HP to provide comparisons with zero, which probably explains why it's the only one until the 41C where the set of comparisons with zero exactly matches the set of comparisons with Y... and the lack of ROM space could also explain why the inequalities are each other's logical opposites, because that saves another couple of steps in their implementation. And finally, the full set of 12 as it exists on the 42S would have been hard to fit on the HP-25 keyboard. The only thing that the 25 had absolutely no shortage of was opcodes.

(02-02-2018 06:59 PM)Dieter Wrote:  But who cares today?
Tempi passati. ;-)

Well, we do. Duh.