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Accuracy of Saturn CPU emulators
01-28-2020, 05:37 AM
Post: #2
RE: Accuracy of Saturn CPU emulators
Um, let's clarify.

'Accuracy' terminology somewhat implies that calculated values are generally correct but maybe there are rounding errors or differences, error accumulations in chain calculations differ somewhat, etc.

With emulation of CPUs like Nuts, Saturns or TI TMS01xx calc processors...

- a bad instruction (i.e, not fully emulated) may result in COMPLETELY WRONG ANSWER
or a trivially wrong one - there can be wide variation, depending on type of math
operation, value, etc.

- calculations not using those bad instruction(s) are NOT AFFECTED. You could have a
machine instruction error that conceivably might only affect the 'arc' trig functions,
say, but not others.

So such errors may be more pattern-based than size/scale based.

A proper CPU emulation with all relvant CPU instructions used in user math operations properly
translated will preserve accuracy 100% - and will also preserve original *inaccuracy* 100%.

As we see somehow on some Saturn ARM emulations, some instructions were not translated properly (or all their modes properly understood).

Testing for accuracy errors might be one way to find errors in instruction translation-mock execution. However, it's probably better to build a testbed for each instruction and its parameters [with poss dependence on prior instructions] and see those execute properly.

Bill Wiese
San Jose CA

(01-27-2020 03:29 PM)ldesnogu Wrote:  Hello,

I am wondering what the most accurate Saturn CPU emulator is (I am talking of the CPU emulator accuracy rather than the full calculator one).

Reading Hrast page about his emulators on HP 49g+/HP 50, it looks like the Saturn emulator used by those calculators was not fully accurate, in particular for BCD computation.

Is Christoph Gießelink and Sébastien Carlier Emu48 the most accurate one? I think I read somewhere that Christoph ran many tests on his calc to ensure accuracy (but can't find the info any more). I wonder how far this was pushed.
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RE: Accuracy of Saturn CPU emulators - bwiese - 01-28-2020 05:37 AM

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