Counting bits in the segmented sieve of Eratosthenes

segmented_bit_sieve2.cpp

// unset bits > limit
if (high == limit)
{
  int64_t bits = 0xff << (limit % 16 + 1) / 2;
  sieve[sieve_size - 1] &= ~bits;
}

// count primes
for (int64_t n = 0; n < sieve_size; n++)
  count += popcnt[sieve[n]];