LONGs with the Bosch sensor
I have read the Bosch datasheet which is very similar to the Intersema MS5540 family. With the exception of absolute altitude, LONGs and a PIC18F part will handle those formulae easily.
The mathematical gymnastics of handling the Bosch 19 bit variables with 16 bit PBP will consume much code space thus ruling out the 12F series. You will get it into a 16F part on code space grounds but you will have to invent your own way to extend WORD variables up to 19 bits. Why bother?
The 18F series costs hardly any more, at least at hobby volumes, so cut your losses and go for a PIC18F part and take advantage of LONGs. This will automatically take care of negative temperatures which your altimeter will certainly need.
Absolute Altitude needs LOG functions to handle the power 1/5.255 so avoid that by using a lookup table which you can make as accurate as you want by adjusting the size of the table and the interpolation method.
HTH
BrianT
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