In order to simplify the use of machine dependent features,
preprocessor variables have been defined which describe particular features.
For example, the declarations of double precision variables in Fortran
is given by the symbol,
DOUBLE_TYPE. On most machines, this
DOUBLE PRECISION, but on the Cray, it
REAL. The source code file, config.h,
contains all these configuration variables. The values are set using
a small number of machine identifiers which are set by the makefiles
used to build CONGEN.