Check this guy out!

[Commie]

Hi Chaps,

I have been looking to design a rpn calculator using ieee 754 32bit binary floats and I have accumplished this with a compiler and an 8051 mcu. So, although the rpn functions correctly( after alot of work and testing), the problem is found to be ieee 754 32bit floats, as most compilers only support.I do have an AVR compiler which supports ieee 754 64bit binary floats at my disposal.

I wrote my own transcandential math functions using the pade algorithm, this is the same as Taylors series except the pade algorithm yields more accuracy because it is a polynomial divided by another polynomial. I tried Cordics, got it working but there wasn't much advantage in it so I continued with the pade algorithm, supported by Derive 6.2 math pc package.
Anyways, ieee 754 32bit binary floats turn out to be a pile of crap.I did not not know this until I prototyped and then the ugly truth revealed itself regarding ieee 754 floats during protyping.I have since realised that commercial calculators use bcd floating point and have done so for many years and for good reason, which yields much better accuracy results.

Now, Alex Garza has developed a HP15c called the PX15c and is avalable as kit or ready built, however the interesting thing is, he has squeezed it into a $3 atmega328 AVR mcu which is totally amazing and I wish him well with his endevours.I believe his design is one that uses NUT cpu emulation.

Well, there you have it, and then I came across this guy from the czech republic and it appears as though he is a real pro, heres the link:

https://www.breatharian.eu/hw/et58/index_en.html

His calculator is open source and I think I'm going to have a go at building it.

Cheers
Darren