Recursive filter - making it go faster

[nazoa]

I have code for a recursive low pass filter which is working OK but I need to increase its speed. The line which is taking too long is the following:

filt1 = filt1 - ( filt1 >> 4 ) + ad_ref;

In this, filt1 and ad_ref are 32bit unsigned integers. A long shot, but I was wondering if anyone can suggest a way of getting this simple code to go faster. At the moment I am running the PIC at 40MHz and the line executes in a little under 5us.

Thanks

[FvM]

I count exactly 46 instruction cycles (4.6 us). int32 arithmetic is quite bulky with PIC18, I don't see an option to speed it up. Switching to assembly coding can't save more than a few register load operations. If you don't need actually 32 bit, there would be room for timing optimizations.

Or use a faster processor, e.g. PIC24.