Optimizing Calculation to Get Length of Longest Sequence of Zero Bytes in Binary File

I need to calculate the length of the longest sequence of zero bytes in a binary file as fast as possible. I have a basic implementation in C++ below:

#include <iostream>
#include <fstream>
#include <algorithm>
#include <string>

int get_max_zero_streak(std::string fname)
{
  std::ifstream myfile(fname, std::ios_base::binary);
  int length = 0;
  int streak = 0;
  while(myfile) 
  {
    unsigned char x = myfile.get(); // unsigned 8 bit integer
    if(x == 0)
    {
      streak += 1;
    }
    else
    {
      length = std::max(length, streak);
      streak = 0;
    }
  }
  return length;
}

int main() 
{
  std::cout << get_max_zero_streak("000_c.aep") << std::endl;
  std::cout << get_max_zero_streak("000_g1.aep") << std::endl;
  std::cout << get_max_zero_streak("000_g2.aep") << std::endl;
  std::cout << get_max_zero_streak("001_c.aep") << std::endl;
  std::cout << get_max_zero_streak("001_g1.aep") << std::endl;
  std::cout << get_max_zero_streak("001_g2.aep") << std::endl;
  std::cout << get_max_zero_streak("002_c.aep") << std::endl;
  std::cout << get_max_zero_streak("002_g1.aep") << std::endl;
  std::cout << get_max_zero_streak("002_g2.aep") << std::endl;
  return 0;
}

This is OK on smaller files, but is extraordinarily slow on larger files (such as 50 GB+). Is there a more efficient way to write this, or is parallelizing it my only hope? I'm reading the files from an NVMe SSD, so I don't think the drive read speed is the limitation.