.

1 files changed, 86 insertions, 0 deletions

diff --git a/src/factor.c b/src/factor.c
new file mode 100644
index 000000000..967799e1c
--- /dev/null
+++ b/src/factor.c
@@ -0,0 +1,86 @@
+/* factor -- print factors of n.  lose if n > 2^32.
+   Copyright (C) 1986 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+/* Written by Paul Rubin <phr@ocf.berkeley.edu>.  */
+
+#include <stdio.h>
+
+void do_stdin ();
+void factor ();
+
+void
+main (argc, argv)
+     int argc;
+     char **argv;
+{
+  if (argc == 1)
+    do_stdin ();
+  else if (argc == 2)
+    factor ((unsigned) atoi (argv[1]));
+  else
+    {
+      fprintf (stderr, "Usage: %s [number]\n", argv[0]);
+      exit (1);
+    }
+  exit (0);
+}
+
+void
+factor (n0)
+     unsigned long n0;
+{
+  register unsigned long n = n0, d;
+
+  if (n < 1)
+    return;
+
+  while (n % 2 == 0)
+    {
+      printf ("\t2\n");
+      n /= 2;
+    }
+  /* The exit condition in the following loop is correct because
+     any time it is tested one of these 3 conditions holds:
+      (1) d divides n
+      (2) n is prime
+      (3) n is composite but has no factors less than d.
+     If (1) or (2) obviously the right thing happens.
+     If (3), then since n is composite it is >= d^2. */
+  for (d = 3; d * d <= n; d += 2)
+    {
+      while (n % d == 0)
+	{
+	  printf ("\t%d\n", d);
+	  n /= d;
+	}
+    }
+  if (n != 1 || n0 == 1)
+    printf ("\t%d\n", n);
+}
+
+void
+do_stdin ()
+{
+  char buf[1000];
+
+  for (;;)
+    {
+      if (fgets (buf, sizeof buf, stdin) == 0)
+	exit (0);
+      factor ((unsigned long) atoi (buf));
+    }
+}