--- Olin Lathrop <olin_piclist@embedinc.com> wrote:
> Which don't contain any description or comments so
> are pointless to try and
> follow.
> 
> What part of your calculations must be done at run
> time versus computed up
> front at assembly time?  Do you really need 64 bits
> of precision (hard to
> imagine why) or just the dynamic range?  If so,
> floating point may be easier
> than very wide integer or fixed point arithmetic. 
> Step back and explain
> what you are trying to accomplish at a higher level.
 

The calculations must all be done at run time, as the
input variable "Fout"  will always change.  Fout can
be 24e9, more than 32 bits, and requires precision in
the tenths place.

Both dynamic range and precision are required, that is
why I am looking for 64 bit math routines.  I cannot
simply scale an imprecise result.

I understand the impulse to ask "Do you really need
what you're asking for?".  Or, "Is there another way
that doesn't require the precision?"  The answer is: I
need the precision.  The application is a microwave
synthesizer operating at frequencies up to 24 X 10^9
Hz, with sub-Herz resolution, a 40-bit number.  To
perform the math without rounding errors requires more
than 40 bits.

Variable "DDS_bits" requires a 48-bit precision
result.  All the inputs to that last equation must be
exact.

I hope that is enough explanation, it probably does
not make sense for me to try and describe the entire
block diagram of the synthesizer in this post.  You
may be sure if there were a mathematically more simple
approach I would have used it.  It may be true that 48
bits are sufficient.

Now that I have taken the time to explain that I need
precision math, will you, if you can, answer my
question?

Regards,

Clay


Fout =    1.212456391800000e+010
a =      118355
seed =      118272
Fref_act =    6.837827795551758e+008
dr =   8.86580086580087
Fdds =    7.026223644140625e+007
DDS_bits =    6.592353788661100e+013


		
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