On Thu, Nov 16, 2006 at 06:58:32PM +1300, Brian Harris wrote:
> I've got a modulo arithmetic question to do with a sensor
> outputting data like this:
> 
> bits 31-26 ID and parity
> bits 25,24,23 modulo counter
> bits 22-0 data (LSB bit = 42.91534 micro degrees)
> 
> The 3-bit modulo counter increments when crossing from 359 to 0 deg
> and decrements when crossing from 0 to 359 deg.
> 
> I want  to find the difference between the current reading of the sensor 
> and the previous reading.
> Using the the least sig bit of the modulo  gives angle polarity but only 
> for the rollover between +-360deg.

It looks to me like what you've really got is a 26 bit angle - the
"modulo counter" bits are just the higher bits of the angle.  Can't you
just subtract the two 26-bit values and look at the sign to work out
which direction it's moved?

Chris
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