This entry is basically my memorandum so that I won't make mistake.
We have type gnupg_fd_t, assuan_fd_t to represent file descriptor of POSIX or HANDLE of Windows.
On 32-bit machine, HANDLE can be represented by int, so, no problem.
On 64-bit machine, it's intptr_t as integer type to represent HANDLE.
For now, it works (as long as the value of HANDLE is small enough), but there are places where we need fix.