int64_t
is guaranteed by the C99 standard to be exactly 64 bits wide on platforms that implement it, there's no such guarantee for a long
which is at least 32 bits so it could be more.
§7.18.1.3 Exact-width integer types 1 The typedef name intN_t designates a signed integer type with width N , no padding bits, and a two’s complement representation. Thus, int8_t denotes a signed integer type with a width of exactly 8 bits.