fir_filter(b,x,y)

function y = fir_filter(b,x,y)
%FIR_FILTER  Finite Impulse Response Filter
%   Y = FIR_FILTER(B,X,Y) filters the data in vector X with the finite
%   impulse response (FIR) filter described by vector B to create the
%   filtered data Y.  The filter implements the moving average:
%     
%     y(n) = b(1)*x(n) + b(2)*x(n-1) + ... + b(nb+1)*x(n-nb)
%
%   where nb = length(b)-1.
%
%   The output vector Y is used as an input to this function so that it
%   will be aware of its data type.

% This M-code was used to produce the plots in the News and Notes article
% Fixed-point Signal Processing: Getting Started, by Darel A. Linebarger 
% and Thomas A. Bryan, 2004.

z = zeros(length(b),1);
for k=1:length(x)
  z = [x(k); z(1:end-1)];
  y(k) = b*z;  % Inner product
end