minix/commands/factor/factor.c
2010-05-12 16:28:54 +00:00

53 lines
885 B
C

/* factor - print the prime factors of a number Author: Andy Tanenbaum */
#include <stdlib.h>
#include <stdio.h>
_PROTOTYPE(int main, (int argc, char **argv));
_PROTOTYPE(long first, (long k));
int main(argc, argv)
int argc;
char *argv[];
{
/* Factor a number */
long i, n, flag = 0;
if (argc != 2 || (n = atol(argv[1])) < 2) {
printf("Usage: factor n (2 <= n < 2**31)\n");
exit(1);
}
if (n == 2) {
printf("2 is a prime\n");
exit(0);
}
while (1) {
i = first(n);
if (i == 0) {
if (flag == 0)
printf("%ld is a prime\n", n);
else
printf("%ld\n", n);
exit(0);
}
printf("%ld ", i);
n = n / i;
flag = 1;
}
}
long first(k)
long k;
{
/* Return the first factor of k. If it is a prime, return 0; */
long i;
if (k == 2) return(0);
if (k % 2 == 0) return (2);
for (i = 3; i <= k / 3; i += 2)
if (k % i == 0) return(i);
return(0);
}