Programming Pearls - disk sort

generate.py

#!/usr/bin/env python3
import random

sample_size = 9000000
numbers = list(range(0, 10000000))
random.shuffle(numbers)

with open('numbers.txt', 'w') as f:
    for i in numbers[0:sample_size]:
        print('{}'.format(i))

main.c

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

int main(int argc, char *argv[]) {
  FILE *file = fopen("numbers.txt", "r");
  FILE *out  = fopen("sorted.txt", "w");
  char line[256];
  int number;
  char vb[10000000 / 8];
  char current;
  char mask;
  int k;

  while (fgets(line, sizeof(line), file)) {
    number = atoi(line);
    k = (int)floor(number / 8);
    current = vb[k];
    mask = 1 << (8 - (number % 8));
    vb[k] = current | mask;
  }

  for (int i = 0; i < 10000000 / 8; i += 1) {
    current = vb[i];

    for (int j = 1; j < 8; j += 1) {
      mask = 1 << (8 - j);

      if (current & (!current | mask) != 0) {
        fprintf(out, "%d\n", i * 8 + j);
      }
    }
  }

  fclose(file);
  fclose(out);

  return 0;
}