Re: RFC: Generic Fixed-Point IIR Filter

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 26 Mar 2015 09:25:25 -0700 (PDT), Patrick Noffke wrote:

> I realize my range and precision for Filter_Value_Type are not
> necessarily ideal (the range depends on the filter coefficients, the
> filter architecture, as well as the filter order).  Do you know of any
> references or have suggestions for how to analyze a filter to determine
> the ideal range and precision?

Intermediate values should have some physical sense. E.g. acceleration when
you calculate dv/dt from v and t. Such values are limited by the process
and thus you could estimate their ranges.

This is also a good argument against using a single fixed-point type in
calculations. This is not a problem with floating-point types as they
designed to accommodate all possible intermediate values of practically any
process, though maybe losing some accuracy. But with fixed-point types one
should go after proper dimensional arithmetic with *different* types of
*different* precision for each physical value, intermediates included.

Unfortunately there is basically no support in Ada (or in any other
language I know) for this.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de