/*
 * fact.c
 *
 * Compute factorial of input integer
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is the MPI Arbitrary Precision Integer Arithmetic library.
 *
 * The Initial Developer of the Original Code is
 * Michael J. Fromberger.
 * Portions created by the Initial Developer are Copyright (C) 1998
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */
/* $Id: fact.c,v 1.3 2004/04/27 23:04:37 gerv%gerv.net Exp $ */

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

#include "mpi.h"

mp_err mp_fact(mp_int *a, mp_int *b);

int main(int argc, char *argv[])
{
  mp_int  a;
  mp_err  res;

  if(argc < 2) {
    fprintf(stderr, "Usage: %s <number>\n", argv[0]);
    return 1;
  }

  mp_init(&a);
  mp_read_radix(&a, argv[1], 10);

  if((res = mp_fact(&a, &a)) != MP_OKAY) {
    fprintf(stderr, "%s: error: %s\n", argv[0],
	    mp_strerror(res));
    mp_clear(&a);
    return 1;
  }

  {
    char  *buf;
    int    len;

    len = mp_radix_size(&a, 10);
    buf = malloc(len);
    mp_todecimal(&a, buf);

    puts(buf);

    free(buf);
  }

  mp_clear(&a);
  return 0;
}

mp_err mp_fact(mp_int *a, mp_int *b)
{
  mp_int    ix, s;
  mp_err    res = MP_OKAY;

  if(mp_cmp_z(a) < 0)
    return MP_UNDEF;

  mp_init(&s);
  mp_add_d(&s, 1, &s);   /* s = 1  */
  mp_init(&ix);
  mp_add_d(&ix, 1, &ix); /* ix = 1 */

  for(/*  */; mp_cmp(&ix, a) <= 0; mp_add_d(&ix, 1, &ix)) {
    if((res = mp_mul(&s, &ix, &s)) != MP_OKAY)
      break;
  }

  mp_clear(&ix);

  /* Copy out results if we got them */
  if(res == MP_OKAY)
    mp_copy(&s, b);

  mp_clear(&s);

  return res;
}