Doped De-Accumulator using BCJR Algorithm ?

Hello, I wrote a matlab code for the doped accumulator

    function [accumulated_bits] = accumulator(uncoded_bits,P)
 accumulated_bits=uncoded_bits;

    coded_bits=zeros(1,length(uncoded_bits));
    coded_bits(1) = uncoded_bits(1);
    for i = 2:length(uncoded_bits)
       coded_bits(i) = mod(coded_bits(i-1)+uncoded_bits(i),2);
    end

    for i=P:P:length(uncoded_bits)
        accumulated_bits(i)=coded_bits(i);
    end

but I didn't find how to implement a decoder for this doped accumulator (using the BCJR algo) Could you help me?