Re: RFC: Generic Fixed-Point IIR Filter

[Patrick Noffke <patrick.noffke@gmail.com>]

On Thursday, March 26, 2015 at 4:12:30 PM UTC-5, Randy Brukardt wrote:
> Right. The rule specifically does not allow something like:
>     A * B * C

Ah, okay.

If I change the calculation to

            Filter.Y (1) := Filter.B (1) * Filter.X (1) +
              Filter.B (2) * Filter.X (2) +
              Filter.B (3) * Filter.X (3) -
              Filter.A (2) * Filter.Y (2) -
              Filter.A (3) * Filter.Y (3);
            Filter.Y (1) := Filter.Y (1) / Filter.A (1);

Then it compiles.  So it didn't like me doing the division with a universal_fixed product as the numerator.

In my case, A(1) is 1.0, but that is not always the case, so there could still be overflow.  I suppose I could change this to a Normalized_IIR_Filter (implying A(1) is 1.0).

Thanks for your help.

Patrick