uint64_t setting a range of bits to 1 [duplicate]

Answer 1

unsigned is unsigned int, so a 32 bits value, as well as constant 1 which is a signed int, so when you're shifting 1 << (high-low + 1) you're doing it on 32 bits integers.

Use ull to transform all your constants to unsigned 64 bits int during the shifts.

mask = ((1ull << (high-low + 1ull))-1ull) << low

Answer 2

You need to make the initial bit into the type unsigned long long (or uint64_t) so that it doesn't overflow when bitshifted.

mask = ((1ULL << (high - low + 1)) - 1) << low;
          ^^^

For number 1 of int type, it'll overflow when leftshifted for 32 bits:

((1 << (high-low + 1))-1) // Where (high-low + 1) == 31 - 0 + 1 == 32
  ^

    00000000 00000000 00000000 00000001 = 1
 v <-- Left shift for 32 bits --------<
(1) 00000000 00000000 00000000 00000000 = 0

But that would work for a 64-bit integer type. So change it to 1ULL and the problem is gone.