25C/29C Conditionals

[Matt Agajanian]

Hi all,

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

Thanks

[Thomas Okken]

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.

[rprosperi]

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.