This is an implementation of the 2000a nutation algorithm as described in The IAU Resolutions on Astronomical Reference Systems, Time Scales, and Earth Rotation Models Explanation and Implementation (George H. Kaplan) and IERS Tech Note 32. I have tested it against the IAU SOFA routine iauNut00a(). A set of test data is available.
The error compared to the IAU SOFA implementation is within 100 pico arcseconds for +/- 10,000 years, which is more than 1000 times more precise than the micro arcsecond accuracy of the 2000a model. But, if exact agreement is needed, then an IAU SOFA implementaiton should be used.