ffi_id_int(-42)         = -42
ffi_id_short(-1234)     = -1234
ffi_id_s64(huge)        = 9000000000000000000
ffi_id_uint(0xDEADBEEF) = 3735928559
ffi_id_ushort(0xFFFF)   = 65535
ffi_id_u64(0x7FEE...)   = 9218551421072305134
ffi_id_schar(127)       = 127
ffi_id_uchar(255)       = 255
ffi_id_f32(3.5)         = 3.500000
ffi_id_f64(1.5)         = 1.500000
ffi_id_ptr roundtrip    = true
ffi_add_int(7, 8)       = 15
ffi_add_double(0.25, 0.75) = 1.000000