ASA005 is a FORTRAN77 library which evaluates the lower tail of the noncentral T distribution, by BE Cooper.
ASA005 is Applied Statistics Algorithm 5. Source code for many Applied Statistics Algorithms is available through STATLIB.
ASA005 is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.
ASA076, a FORTRAN77 library which evaluates the Owen's T function, needed to compute the CDF of the noncentral T distribution.
ASA243, a FORTRAN77 library which evaluates the CDF of the noncentral T distribution.
OWENS, a FORTRAN77 library which evaluates Owen's T function.
Original FORTRAN77 version by BE Cooper; This FORTRAN77 version by John Burkardt.
You can go up one level to the FORTRAN77 source codes.