You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: snr_fwd_dsss.m
    path of file: ./repos/mpsim/lib/snr/fwd
    
    the code of the file until where you have to start completion: % Direct-sequence spread-spectrum (DSSS) modulation -- 
% currently only binary phase shift keying (BPSK), for both GPS and GLONASS.
function [delay_replica, phasor_replica, delay_update, ...
phasor_direct_post, phasor_reflected_post, phasor_reflected_post_net, ...
correl_direct, correl_reflected] ...
= snr_fwd_dsss (opt, ...
phasor_direct_pre, phasor_reflected_pre, ...
delay_reflected, doppler_reflected, ...
delay_replica)
    %TODO: add test for PO
    %TODO: stress test for PO large-magnitude reflections (hint: material_bottom = 'pec';  ant_model = 'isotropic';  ant_radome = '';)
    %TODO: make tests pass for coherent 
    
function of number of chips 
    % (its mathematical definition is given on p.20-21 of the textbook;
    % this particular implementation is given on p.105):
     answer = (1 - abs(delay_in_chips)) .* heaviside(1 - abs(delay_in_chips));
    %answer = (1 - abs(delay_in_chips)) .*     (0 < (1 - abs(delay_in_chips)));
    % the textbook is Borre, Akos et al., "GPS SDR".
    %TODO: support BOC modulation (is it just a diff DSS correl fnc?).
end

function [phasor_replica, phasor_direct_post, ...
phasor_reflected_post, phasor_reflected_post_net, ...
correl_direct, correl_reflected] ...
= get_dsss_correlation_composite (opt, ...
phasor_direct_pre, phasor_reflected_pre, ...
delay_reflected, doppler_reflected, ...
delay_replica, delay_offset)
    if (nargin < 6) || isempty(delay_replica),  delay_replica = 0;  end