ex1c.c File Reference

Appfs Exercise 1: memory mapped file input. More...

#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>

Go to the source code of this file.

Macros
#define	MAX_NUMS   ((INT_MAX >> 5) + 1)
	Maximum number of 32 bit ints we need to store bits. More...

Functions
int	main (int argc, char **argv)
	Program to read a file with binary positive 32 bit integers, sort the numbers and print them sorted. More...

Detailed Description

Author

Thorsten Koch

Date

18Oct2014

gcc -O3 -Wall -std=c99 -o ex1c ex1c.c

Use memory mapped file for input

Definition in file ex1c.c.

Macro Definition Documentation

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

Definition at line 21 of file ex1c.c.

Function Documentation

int main	(	int	argc,
		char **	argv
	)

Actually, the numbers are not sorted. There is an array with one bit for each possible number. Upon reading the respective bit is set for the number recognized. At the end the array is scanned in order and the numbers present are printed.

Parameters

argv	[1] name of file to read

Definition at line 31 of file ex1c.c.

{
   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;
}