25C/29C Conditionals
10-09-2021, 09:38 PM
Post: #1
 Matt Agajanian Senior Member Posts: 542 Joined: Dec 2013
25C/29C Conditionals
Hi all,

Why did HP use different x/y conditional between these two Woodstock models?

Thanks
10-10-2021, 12:02 AM
Post: #2
 Thomas Okken Senior Member Posts: 1,357 Joined: Feb 2014
RE: 25C/29C Conditionals
Educated guess:

The early programmable models with eight comparison functions, that is, the 25/25C, 19C/29C, 67/97, 33E/33C, 11C, and 16C, all have the same set: X=0, X≠0, X<0, X>0, X=Y, X≠Y, X≤Y, and X>Y, except for the 25/25C, which has X=0, X≠0, X<0, X≥0, X=Y, X≠Y, X<Y, and X≥Y.

So the 25/25C are different, and I suspect it is significant that the comparison functions on those calculators are more symmetrical: the comparisons with 0 exactly match those with Y, and all comparisons consist of pairs that are exactly complementary. This would have made it possible to implement the 25/25C comparison functions using less code, and given that the HP-25 ROM is completely full, that may have been the only way they could make everything fit.
10-10-2021, 02:38 AM
Post: #3
 rprosperi Senior Member Posts: 5,016 Joined: Dec 2013
RE: 25C/29C Conditionals
Also, recall the 25 was released almost a year before the 67 and 18 months before the 29C, and during this time HP was very active refining both internal machine code and the user programming languages, so it's reasonable to conclude the '29C style' conditionals were deemed improvements, and more likely to be useful more often than the earlier style. Not an exact reply, as program needs vary, but overall those guys have a pretty good track record for making good choices when trying to improve things.

--Bob Prosperi
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