On 11/04/2015, Eric Christiansen <eric8939...@gmail.com> wrote: > I haven't done much with SIMD in the past, so my experience is pretty low, > but my understanding is that each data piece must be defined prior to the > operation, correct? Meaning that you can't use result of the operation of > one piece of data as the source data for the next operation, right? > > This came up in thinking about how to optimize an anti-aliasing routine. > If, for example, the process is oversampling by 4 and running each through > a low pass filter and then averaging the results, I was wondering if > there's some way of using some SIMD process to speed this up, specifically > the part sending each sample through the filter. Since each piece has to go > through sequentially, I would need to use the result of the first filter > tick as the input for the second filter tick. > > But that's not possible, right?
Technically you can do it, by keeping the previous result in some temporary register, but since you cannot parallelize the recursion (unless you have actual parallel filters), it rarely gives much speedup for IIR filters, if any. So it's probably not worth the hassle for recursive filters. Quote from a post from 2007: ----- Original Message ----- From: "Eric Brombaugh" <ebrombaugh at earthlink.net> To: "A discussion list for music-related DSP" <music-dsp at music.columbia.edu> Sent: Friday, October 05, 2007 11:38 PM Subject: Re: [music-dsp] Cascaded biquad filter structures > You can vectorize a cascade of biquads if you're willing to accept some > transport delay - just insert pipelines between the stages to hold the > previous results. > > A few years back I coded up an FIR and an IIR biquad in SSE. I got about > 2x speed improvement in the FIR version over plain optimized GCC with > floats, but the IIR implementation was about 70% slower in SSE than plain > optimized GCC. -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp
