> you REALLY don't want to use floating point on a PIC.

There are cases where floating point is quite useful, even on a PIC.  Most
of the time fixed point is appropriate, but sometimes the combination of
precision and dynamic range make fixed point impossible to use without
storing rediculously large (many byte) values.  Floating point is also
easier and less prone to programming errors because all the binary point
tracking is handled automatically and the precision is more predictable.

We have developed a library of 24 bit floating point routines that use 1
sign bit, 7 exponent bits, and 16 mantissa bits.  These have worked well in
several projects, including one project which used two nested PID
controllers to regulate the speed of a gasoline engine.  All the PID
calculations were in floating point with the worst case execution time of
7mS.  This fit well with the 10mS (100Hz) output update rate.


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