[Croatoan]

Can sb give me a tip for recursive multiplication of two binary numbers (their lenght is 2^n)! I need only recursive to implement it in c++ code,

[xpi0t0s]

What's recursive multiplication? Could you outline the algorithm, i.e. how would you do it on paper?

[Croatoan]

x=xl * 2^(n/2)+xr (n=2^k, k e 1,2,3)
y=yl * 2^(n/2)+yr

x*y=xl * 2^(n/2) * yl * 2^(n/2) + xl * 2^(n/2) * yr +
xr*yl * 2^(n/2) + xr*yr

how to implement that in c++

[xpi0t0s]

Where are you stuck?
2^(n/2) appears to be a constant (let's say you put that in c), so the first equation
x=xl*c+xr
translates into C++ as
x=xl*c+xr;

You should be able to take it from there.