Sigma Delta calculation of SNR

can anyone pls explain this code to me:

function outx = sinusx(in,f,n)
%
% Extraction of a sinusoidal signal
%
sinx=sin(2*pi*f*[1:n]);
cosx=cos(2*pi*f*[1:n]);
in=in(1:n);
a1=2*sinx.*in;
a=sum(a1)/n;
b1=2*cosx.*in;
b=sum(b1)/n;
outx=a.*sinx + b.*cosx;

and also this one:

function [snrdB,ptotdB,psigdB,pnoisedB] = calcSNR(vout,f,fB,w,N,Vref)
% SNR calculation in the time domain (P. Malcovati, S. Brigati)
% vout: Sigma-Delta bit-stream taken at the modulator output
% f: Normalized signal frequency (fs -> 1)
% fB: Base-band frequency bins
% w: windowing vector
% N: samples number
% Vref: feedback reference voltage
%
% snrdB: SNR in dB
% ptotdB: Bit-stream power spectral density (vector)
% psigdB: Extracted signal power spectral density (vector)
% pnoisedB: Noise power spectral density (vector)
%
fB=ceil(fB);
signal=(N/sum(w))*sinusx(vout(1:N).*w,f,N); % Extracts sinusoidal signal
noise=vout(1:N)-signal; % Extracts noise components
stot=((abs(fft((vout(1:N).*w)'))).^2); % Bit-stream PSD
ssignal=(abs(fft((signal(1:N).*w)'))).^2; % Signal PSD
snoise=(abs(fft((noise(1:N).*w)'))).^2; % Noise PSD
pwsignal=sum(ssignal(1:fB)); % Signal power
pwnoise=sum(snoise(1:fB)); % Noise power
snr=pwsignal/pwnoise;
snrdB=dbp(snr);
norm=sum(stot)/Vref^2; % PSD normalization
if nargout > 1
ptot=stot/norm;
ptotdB=dbp(ptot);
end

if nargout > 2
psig=ssignal/norm;
psigdB=dbp(psig);
end

if nargout > 3
pnoise=snoise/norm;
pnoisedB=dbp(pnoise);
end

i am starting to study how sigma delta ADCs work and i would very much appreciate if anyone can explain the codes above to me found in Richard Schreier's Understanding Delta-Sigma Data Converters.