Tips on Spline fitting and arc length calculation

I have large data sets with around 5000 values for an x and y array. I am trying to determine the arc length of these arrays using piecewise spline fits. I am able to retrieve the coefficients and break points of the pieces however the while loop I am using takes too long to calculate the arc length of 5000 4th order splines. I was wondering if anyone has any suggestions to shorten the time needed or use a different function for piecewise splines. I am using cspai currently to get my break and coefs for the pieces.