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/*
* fact.c
*
* Compute factorial of input integer
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#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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