  The R functions .C() and .Fortran() can be used to call compiled C/C++ and
Fortran code from R. This so-called foreign function interface is convenient,
since it does not require any interactions with the C API of R. However, it
does not support long vectors (i.e., vectors of more than 2^31 elements). To
overcome this limitation, the R package dotCall64 provides .C64(), which can be
used to call compiled C/C++ and Fortran functions. It transparently supports
long vectors and does the necessary castings to pass numeric R vectors to
64-bit integer arguments of the compiled code. Moreover, .C64() features a
mechanism to avoid unnecessary copies of function arguments, making it
efficient in terms of speed and memory usage.
