file permission

filepermission.c

/* filepermission.c
 * 
 * Date: 11/01/2012
 *
 */

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

int pack_value(int,int,int);
int unpack_value(int,int,int);
void get_date(int holder,int *a,int *b,int *c);
void get_permissions(int,int,int *, int *, int *);

int main() {
	int day,month,year;
	printf("Date\n");
	printf("Enter a day: ");
	scanf("%d",&day);
	printf("Enter a month: ");
	scanf("%d",&month);
	printf("Enter a year: ");
	scanf("%d",&year);
	
	if (day >31) {
		printf("attempt to store %d in 5 bits\n",day);
		exit(1);
	}
	else if (month > 12) {
		printf("attempt to store %d in 4 bits\n",month);
		exit(1);
	}
	else if (year > pow(2,12)) {
		printf("attempt to store %d in 32 bits\n",year);
		exit(1);
	}
	
	int date = pack_value(day,5,0)|pack_value(month,4,5)|pack_value(year,12,20);
	printf("The date is %d\n",date);
	
	get_date(date,&day,&month,&year);
	printf("day: %d, month: %d, year: %d\n\n",day,month,year);

	char read,write,execute;
	int count = 0;
	char *users[] = {"owner","groups","others"};
	/*while (count < 3) {
		printf("\nPermissions for %s:\n", users[count]);
		printf("\tread: ");
		scanf("%c",read);
		printf("\twrite: ");
		scanf("%c",write);
		printf("\texecute: ");
		scanf("%c",execute);
		count++;
	}*/
	printf("\nPermissions for owner:\n");
	printf("\tread: ");
	scanf("%c",read);
	printf("\twrite: ");
	scanf("%c",write);
	printf("\texecute: ");
	scanf("%c",execute);

	int owner = pack_value(read,2,1)|pack_value(write,2,4)|pack_value(execute,2,7);
	
}

int pack_value(int value, int size, int low_bit) {
	int bitmask = pow(2,size)-1;
	int newVal = value&0xfffff;
	printf("newval: %d\n",newVal);
	if (newVal != value) {
		printf("value is too high. Exiting...\n");
		exit(1);
	}
	return newVal << low_bit;
}

int unpack_value(int holder, int size, int low_bit) {
	int bitmask = pow(2,size)-1;
	int newVal = holder&(bitmask<<low_bit);
	return newVal >> low_bit;
}

void get_date(int holder, int *day, int *month, int *year) {
	*day = unpack_value(holder,5,0);
	*month = unpack_value(holder,4,5);
	*year = unpack_value(holder,12,20);
}

void get_permissions(int permission_int, int class, int *read, int *write, int *execute) {

}