SQRT(P**2 + Q**2)
Moler and Morrison have described a fast algorithm for computing SQRT(P**2+Q**2). This algorithm has cubic convergence. It means that the result is accurate to 6.5 decimal digits after two iterations, to 20 digits after three iterations, and to 62 digits after four iterations.
Unit: internal function, external function without procedure statement
Parameters: numbers P, Q, a positive integer IterCount - number of iterations
Returns: value SQRT(P**2+Q**2) with IterCount**3 decimal digits
Bentley J., Programming Pearls
CACM, December 1986, Vol. 29, No. 12, p. 1161