sig=shiftcircular(sig,shifttime)

function sig=shiftcircular(sig,shifttime)
% shift the period in time circlular
% if shifttime > 0then circle positiv, otherwise negative


bin=time2bin(sig,shifttime);
nrpoints=getnrpoints(sig);
if bin<1
    bin=nrpoints+bin;
end

if bin>nrpoints
	bin=mod(bin,nrpoints);
end

vals=getvalues(sig);
valnew=zeros(size(vals));

valnew(1:bin)=vals(end-bin+1:end);
valnew(bin+1:end)=vals(1:end-bin);

sig=setvalues(sig,valnew);