c@174: function maxabsdiff=tailscrap()
c@174: % test code for circular convolution with the scrapped portion 
c@174: % at the tail of the buffer, rather than the front
c@174: %
c@174: % The idea is to rotate the zero-padded h (impulse response) buffer
c@174: % to the left nh-1 samples, rotating the junk samples as well.
c@174: % This could be very handy in avoiding buffer copies during fast filtering.
c@174: nh=10;
c@174: nfft=256;
c@174: 
c@174: h=rand(1,nh);
c@174: x=rand(1,nfft);
c@174: 
c@174: hpad=[ h(nh) zeros(1,nfft-nh) h(1:nh-1) ]; 
c@174: 
c@174: % baseline comparison
c@174: y1 = filter(h,1,x);
c@174: y1_notrans = y1(nh:nfft);
c@174: 
c@174: % fast convolution
c@174: y2 = ifft( fft(hpad) .* fft(x) );
c@174: y2_notrans=y2(1:nfft-nh+1);
c@174: 
c@174: maxabsdiff = max(abs(y2_notrans - y1_notrans))
c@174: 
c@174: end