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/*
* fact.c
*
* Compute factorial of input integer
*
* 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 Michael J. Fromberger are
* Copyright (C) 1998, 1999, 2000 Michael J. Fromberger.
* All Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the
* terms of the GNU General Public License Version 2 or later (the
* "GPL"), in which case the provisions of the GPL are applicable
* instead of those above. If you wish to allow use of your
* version of this file only under the terms of the GPL and not to
* allow others to use your version of this file under the MPL,
* indicate your decision by deleting the provisions above and
* replace them with the notice and other provisions required by
* the GPL. If you do not delete the provisions above, a recipient
* may use your version of this file under either the MPL or the GPL.
*
* $Id$
*/
#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;
}
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