angle2rotate.m

Cordic算法的Matlab实现

%% decriptioin
% this file is very important for at least two reasons.
% the one is DATAs, which is suppose to be stored in ROM,
% will be provided in the first part of the routine. The
% other is, in fact, it has great effect on the steps of 
% iteration.Of course, the angle to rotate at each step
% is based on the stored DATAs. And angles will be chosen
% to get the result as quickly as possible accordingly.
% How many DATAs are required to obtain the acceptable 
% results,further study is badly needed.
% inputs
%       y or z can be both chosen to decrease.HOWEVER,
%       the same algorithm was employed.
%       NumofData and wordwidth offer the parameters to 
%       generate those DATAs. The method is discussed 
%       below.
%           Since wordwidth limits range of the datas, 
%           and the smallest angle to rotate is 
%           arctan(2^(-wordwidth)),the second smallest
%           one is arctan(2^(-wordwidth+1)), and so on.
%           There will be NumOfData of those smallest
%           datas generated and stored unless the last
%           parameter is provided.Or those angles are 
%           defined in ROM.
% outputs
%       out, the best choice for the places to shift
%       and the current angle to rotate
%           format  Fi arctan(2^(-Fi))
% data format in ROM
%               F0 arctanh(2^-(F0))
%               F1 arctanh(2^-(F1))
%               ...
%            and so on

%% code
function [Fi ei]=Angle2rotate(z,m,wordwidth,NumOfData,ROM)
% DATAs generator
if(nargin<4)
    wordwidth=64;
end
if(nargin<5)
    NumOfData=wordwidth+1;
end
if(nargin<6)
    % F is in an increasing order
    F=wordwidth-(NumOfData-1:-1:0)';
    theta=2.^(-F);
    if(m~=-1)
        ROM=[F atan(theta)];
    else% m=-1
        ROM=[F atanh(theta)];
        if(~F(1))% F0=0 must be removed
            ROM=[F(2:end),atanh(theta(2:end))];
        end
    end
save ROM.dat ROM -ascii
end

% FIND THE BEST CHOICE FOR ANGLE TO ROTATE
% there's only one angle stored
if(NumOfData==1 || length(ROM)==1)
    Fi=ROM(1);ei=ROM(2);
% there's more than one choice
else% find the minumal difference
    for i=1:length(z)
        Remaider=abs(z(i,1));
        [v,index]=min(abs(Remaider-ROM(:,2)));
        % v is useless
        Fi(i)=ROM(index(1),1);
        ei(i)=ROM(index(1),2);
    end
    Fi=Fi';ei=ei';
end
% ends function
end