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function [y,e1]=convol(h,x,e0)
// convol - convolution
//%CALLING SEQUENCE
// [y]=convol(h,x)
// [y,e1]=convol(h,x,e0) (for use with overlap add method)
//%PARAMETERS
// x,h :input sequences (h is a "short" sequence, x a "long" one)
// e0 : old tail to overlap add (not used in first call)
// y : output of convolution
// e1 : new tail to overlap add (not used in last call)
//%DESCRIPTION
// calculates the convolution y= h*x of two discrete sequences by
// using the fft. overlap add method can be used.
//%USE OF OVERLAP ADD METHOD
// For x=[x1,x2,...,xNm1,xN]
// First call : [y1,e1]=convol(h,x1)
// Subsequent calls : [yk,ek]=convol(h,xk,ekm1)
// Final call : [yN]=convol(h,xN,eNm1)
// Finally y=[y1,y2,...,yNm1,yN]
//!
// Copyright INRIA
[lhs,rhs]=argn(0)
n=prod(size(x))
m=prod(size(h))
m1=2^(int(log(n+m-1)/log(2))+1)
x(m1)=0;h(m1)=0
if norm(imag(x))==0&norm(imag(h))==0 then
y=real(fft(fft(matrix(x,1,m1),-1).*fft(matrix(h,1,m1),-1),1))
else
y=fft(fft(matrix(x,1,m1),-1).*fft(matrix(h,1,m1),-1),1)
end
if lhs+rhs==5 then,
e0(n)=0;//update carried from left to right
e1=y(n+1:n+m-1)
y=y(1:n)+e0
elseif lhs+rhs==4 then
if rhs==2 then
e1=y(n+1:n+m-1)
y=y(1:n) //initial update
else
e0(n+m-1)=0 //final update
y=y(1:n+m-1)+e0
end,
else
y=y(1:n+m-1) //no update
end
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