c++ - in bitset, can i use "to_ulong" for a specific range of bits?

Question

I'm working on something that requires me to get access to specific bits and ranges of bits. I decided to use bitset because it is easy to get access to specific bits; how can I extract a range (subset) of bits?

Answer 1

Method A:

return (the_bitset >> start_bit).to_ulong();

Method B (faster than method A by 100 times on my machine):

unsigned long mask = 1;
unsigned long result = 0;
for (size_t i = start_bit; i < end_bit; ++ i) {
    if (the_bitset.test(i))
       result |= mask;
    mask <<= 1;
}
return result;