Efficient way to compute the exponentiation of a fraction and an integer

gistfile1.txt

// https://ethereum.stackexchange.com/a/10432/24989
// Approximate solution using the binomial expansion
// The following is a decent, low-cost approximation:

// Computes `k * (1+1/q) ^ N`, with precision `p`. The higher
// the precision, the higher the gas cost. It should be
// something around the log of `n`. When `p == n`, the
// precision is absolute (sans possible integer overflows). <edit: NOT true, see comments>
// Much smaller values are sufficient to get a great approximation.
function fracExp(uint k, uint q, uint n, uint p) returns (uint) {
  uint s = 0;
  uint N = 1;
  uint B = 1;
  for (uint i = 0; i < p; ++i){
    s += k * N / B / (q**i);
    N  = N * (n-i);
    B  = B * (i+1);
  }
  return s;
}