Bug in the HP-41 with R/S and stack lift

[Valentin Albillo]

(11-02-2020 01:15 PM)Ángel Martin Wrote:  I keep assuming that ST+ puts the X value in LastX, which it does not.... counter-intuitive for me.

Counter-intuitive ? Why ?

In general, only instructions that do change X are expected to copy the previous value of X to the LastX register.

As STO operations do not change the value in X (except if X is the addressed register, of course) they should not copy the contents of the X register to LastX. That would be counter-intuitive, and wrong. On the other hand, RCL+, RCL-, RCLx and RCL/ do change X and thus the previous X is indeed copied to LastX, as it should.

You're getting old, Ángel.

Best regards.
V.