The function statement involves type, name, and formal arguments.
If type is not present in the FUNCTION statement, then the type of the function is determined by default and by any subsequent IMPLICIT or type statement. If type is present, then the function name cannot appear in other type statements.
Compiling with any of the options -dbl, -r8, -i2, or -xtypemap can alter the default data size assumed in the call to or definition of functions unless the data type size is explicitly declared. See Chapter 2 and the Fortran User Guide for details on these options.