diff ext/kissfft/test/tailscrap.m @ 409:1f1999b0f577

Bring in kissfft into this repo (formerly a subrepo, but the remote is not responding)

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ext/kissfft/test/tailscrap.m	Tue Jul 21 07:34:15 2015 +0100
@@ -0,0 +1,26 @@
+function maxabsdiff=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=rand(1,nh);
+x=rand(1,nfft);
+
+hpad=[ h(nh) zeros(1,nfft-nh) h(1:nh-1) ]; 
+
+% baseline comparison
+y1 = filter(h,1,x);
+y1_notrans = y1(nh:nfft);
+
+% fast convolution
+y2 = ifft( fft(hpad) .* fft(x) );
+y2_notrans=y2(1:nfft-nh+1);
+
+maxabsdiff = max(abs(y2_notrans - y1_notrans))
+
+end