test code for avoiding buffer copies of output in fast conv filtering

test/tailscrap.m

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