MATLAB: Speeding up a function

speedvectorization

Hi all, I have the following function that takes x which is a unit32 vector of about 2 billion elements. Basically it expands the decimal numbers and then classify each element based on the structure of the binary string:
function class = classX( x )
class=uint32(zeros(size(x)));
parfor i=1:length(x)
    binary=de2bi(x(i),32);
    if binary(1)==0 && binary(2)==0
        class(i)=1;
    elseif binary(1)==0 && binary(2)==1
        class(i)=2;
    end
end
I'm looking for a possible way to speed this function as much as possible. I look forward to your creative ideas.
AD

Best Answer

Ok, somehow my post got deleted. I asked whether you have other classes or there are just these two classes.
here is a sample:
fprintf('Initiating a sample vector ...');tic
xSize=1e6;
x=randi(xSize,[xSize ,1],'single'); 
fprintf('- took %0.2f[s].\n',toc);
fprintf('Running a serial version of the code ...');tic;
tmpVar=de2bi(x(:));
classList=uint8([1 0 2 0])';
%binary(1), binary(2), decimal value, class
%   0     ,     0    ,        0     ,   1
%   0     ,     1    ,        1     ,   0
%   1     ,     0    ,        2     ,   2
%   1     ,     1    ,        3     ,   0
type=classList( bi2de(tmpVar(:,1:2)) +1);
fprintf('- took %0.2f[s].\n',toc);
pay attention to how classList is created. You can use this to classify them into as many classes as you want and the execution time does not change. This is usually better when dealing with integer classes relative to the case when you want to do logical indexing. Checking conditions take longer cycles.
Note that this code is in serial; On my system it takes about 0.36 seconds for 1M elements, and it takes about 3.73 for 10M elements. So if it holds the same ratio (which most possibly won't) for 2B elements it should take about 750seconds. However, this is serial. No parallel at all.
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