Hi Al, thanks for sending the source and executable for FPREP.

Since then I've been looking at an application which requires f/p
calculations including a 5th order polynomial and natural logarithms.
There are too many variables involved to use lookup tables.

I'm still searching for a way to handle the log; there may
be an easy algorithm to compute log base 2 and then multiply
by a constant to get the natural log.

Another problem is how to convert Microchip's modified IEEE f/p
format into BCD so I can display it on the LCD. Ideally I'd like
the result in engineering format so that I could use the exponent
to locate the decimal point on the LCD.

The typical 4-digit LCD with all display elements turned on looks
like this: 8.8.8.8. The range of values this can display in normal
format is "0.001" to "9999".

None of the current C compilers seem to support a float data type
with a library like math.lib, nor do they have anything like
sprintf().

Originally my client wanted to use a PIC for this application but
after discussing the complexity of the math involved we decided to
use a processer for which a compiler was available with floating
point built in.

I think the PIC would be able to handle a simpler requirement such
as y = ax + b where x is an acquired value (via a/d, etc); a and b
are f/p calibration constants which may be user settable and
therefore of arbitrary value. Although I could check the user's
input for a valid range, I would still need to determine the
location of the decimal point for the displayed value y.

One thing I would try here is to multiply a & b by 1000 so that
the result Y would ends up 1000 times its actual value y. If
the smallest non-zero displayable value y = 0.001 then Y = 1; for
the largest y = 9999, Y = 9,999,000 which is expressable with 24
bits; this would require the 32-bit f/p library. AN575 does have a
conversion for f/p to integer which I could then convert to BCD
fairly easily. A range check would determine where the decimal point
belonged. However, if there's an easier way to do this I'd
appreciate hearing about it -- surely this must be a common
application for the PIC.

Regards, D.M.