QD, double–double and quad double package. QD (A C++/Fortran-90 double-double and quad-double package) Unix-based systems (including Apple Macintosh systems): qd-2.3.17.tar.gz. Before downloading or installing this software, please read LBNL-BSD-License.doc (which contains license information) and the README file. This package supports both a double-double datatype (approx. 32 decimal digits) and a quad-double datatype (approx. 64 decimal digits). The computational library is written in C++. Both C++ and Fortran-90 high-level language interfaces are provided to permit one to use convert an existing C++ or Fortran-90 program to use the library with only minor changes to the source code. In most cases only a few type statements and (for Fortran-90 programs) read/write statements need to be changed. PSLQ and numerical quadrature programs are included.