add directory study

study/linux-travel/MINIX-1.5/1.5/Source/commands/factor.c

@@ -0,0 +1,47 @@
+/* factor - print the prime factors of a number      Author: Andy Tanenbaum */
+
+main(argc, argv)
+int argc;
+char *argv[];
+{
+/* Factor a number */
+
+  long i, n, flag = 0, first(), atol();
+
+  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);
+}