ex1c.c

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#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>

#define MAX_NUMS  ((INT_MAX >> 5) + 1)  


int main(int argc, char** argv)
{
   const char* usage = "usage: %s filename\n";

   /* made static, because otherwise, the stack size might be too small.
    */
   static unsigned int have_num[MAX_NUMS];

   struct stat stat;
   int*        map;
   int         fd;
   int         total_nums = 0;

   /* we assume 32 bit integers, otherwise it will not work
    */
   assert(sizeof(int) == 4);
   
   /* Check arguments, we need a filename.
    */
   if (argc < 2)
   {
      fprintf(stderr, usage, argv[0]);
      exit(EXIT_FAILURE);
   }
   memset(have_num, 0, sizeof(have_num)); // Proably uneccessary

   /* Open file
    */
   if (0 > (fd = open(argv[1], O_RDONLY)))
   {
      perror(argv[1]);
      exit(EXIT_FAILURE);
   }

   if (fstat(fd, &stat))
   {
      perror("fstat: ");
      exit(EXIT_FAILURE);
   }
      
   if (MAP_FAILED == (map = mmap(0, stat.st_size, PROT_READ, MAP_SHARED, fd, 0)))
   {
      close(fd);
      perror("mmap: ");
      exit(EXIT_FAILURE);
   }
       
   /* Read from file until data exhausted
    */
   total_nums = stat.st_size / sizeof(int);

   for(int i = 0; i < total_nums; i++)
   {
      /* Check input: really >= 0 ? Otherwise ignore
       */
      if (map[i] >= 0)
      {
         int          idx = map[i] >> 5;         // n / 32
         unsigned int msk = 1 << (map[i] & 31);  // bit number n mod 32 

         assert(idx >= 0 && idx < MAX_NUMS);
            
         have_num[idx] |= msk;
      }
   }

   if (munmap(map, stat.st_size))
   {
      perror("munmap: ");
      exit(EXIT_FAILURE);
   }
   if (close(fd))
   {
      perror("close: ");
      exit(EXIT_FAILURE);
   }

   fprintf(stderr, "Total numbers read = %d\n", total_nums);
   
   for(int i = 0; i < MAX_NUMS; i++)
      if (have_num[i])  // just for speed up
         for(int k = 0; k < 31; k++)
            if (have_num[i] & (1 << k))
               printf("%d\n", (i << 5) + k);

   return EXIT_SUCCESS;
}