HP Fortran Programmer's Guide (B3908-90031; September 2011)

Compiling and linking
Special-purpose compilations
Chapter 296
However, the C language has some differences in data type sizes. If your Fortran program calls functions
written in C and is compiled in 64-bit mode, the size differences may require promoting the data items that
are passed to or from the C functions. See Table on page 181 and Table on page 181 for the size differences
between Fortran and C data types when compiled in 64-bit mode.
NOTE If your program does not need to run in 64-bit mode, there is no benefit to compiling it in
64-bit mode. In fact, the executable program may run slower than if compiled in 32-bit
mode.