Calculations on large numbers

[Tom Jetland]

Hi,

I'm getting 3 simultaneous values from a sensor as signed ints with a max value of 650,000 (decimal).

I need to perform the following function on them: -

result = SquareRoot( (a^2) + (b^2) + (c^2))

Just to get started I used floating point numbers, but because I need very high precision and repeatability I know that I'll have to used integers.

How do I deal with numbers in the 64 bit range, i.e. the value I would get when squaring the 650,000?

I've looked around at the GNU big number libraries, but to be honest, I had a job understanding it!

Any input would be much appreciated!

I'm using a PIC18F4620.

Tom

[SherpaDoug]

Unless I was going to do a lot of other math with these big numbers I would write my own function to take 3 32 bit ints and return a 32 bit int using a 48 bit intermediate result. The square root is the only thing that would be difficult.
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