i = S[n-1] + 256 * S[n-2] + 256^2 * S[n-3] + ... + 256^(n-1) * S[0]9

 

 

(S(n-1)+256 S(n-2)+256^2 S(n-3)+...+256^(n-1) S(0) 9) = sum_(k=1)^n 256^(-1+k) S(1-k) = sum_(k=1)^n 256^(k-1) S(1-k)

 

i = sum_(k=1)^n 256^(k-1) S(1-k)