How to make the if statement more faster?

I have an if statement as follows:

coeff = zeros(1,255);
for ii = 1:255
    if (alpha1 == 0)
        error('Trying to retrieve the multiplicative inverse of 0!')
    elseif (alpha1 == 1)
        coeff(ii) = ii;        
    elseif (ii == 1)
        coeff(ii) = alpha1;
    else
        coeff(ii) = func( ii, alpha1 );
    end
end

where func is another function. How could I make my code faster because when I check time-consuming, the elseif state takes a lot of time? Thanks