Chris@184: function maxabsdiff=tailscrap()
Chris@184: % test code for circular convolution with the scrapped portion 
Chris@184: % at the tail of the buffer, rather than the front
Chris@184: %
Chris@184: % The idea is to rotate the zero-padded h (impulse response) buffer
Chris@184: % to the left nh-1 samples, rotating the junk samples as well.
Chris@184: % This could be very handy in avoiding buffer copies during fast filtering.
Chris@184: nh=10;
Chris@184: nfft=256;
Chris@184: 
Chris@184: h=rand(1,nh);
Chris@184: x=rand(1,nfft);
Chris@184: 
Chris@184: hpad=[ h(nh) zeros(1,nfft-nh) h(1:nh-1) ]; 
Chris@184: 
Chris@184: % baseline comparison
Chris@184: y1 = filter(h,1,x);
Chris@184: y1_notrans = y1(nh:nfft);
Chris@184: 
Chris@184: % fast convolution
Chris@184: y2 = ifft( fft(hpad) .* fft(x) );
Chris@184: y2_notrans=y2(1:nfft-nh+1);
Chris@184: 
Chris@184: maxabsdiff = max(abs(y2_notrans - y1_notrans))
Chris@184: 
Chris@184: end