michael@0: /*
michael@0:  * fact.c
michael@0:  *
michael@0:  * Compute factorial of input integer
michael@0:  *
michael@0:  * This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #include <stdio.h>
michael@0: #include <stdlib.h>
michael@0: #include <string.h>
michael@0: 
michael@0: #include "mpi.h"
michael@0: 
michael@0: mp_err mp_fact(mp_int *a, mp_int *b);
michael@0: 
michael@0: int main(int argc, char *argv[])
michael@0: {
michael@0:   mp_int  a;
michael@0:   mp_err  res;
michael@0: 
michael@0:   if(argc < 2) {
michael@0:     fprintf(stderr, "Usage: %s <number>\n", argv[0]);
michael@0:     return 1;
michael@0:   }
michael@0: 
michael@0:   mp_init(&a);
michael@0:   mp_read_radix(&a, argv[1], 10);
michael@0: 
michael@0:   if((res = mp_fact(&a, &a)) != MP_OKAY) {
michael@0:     fprintf(stderr, "%s: error: %s\n", argv[0],
michael@0: 	    mp_strerror(res));
michael@0:     mp_clear(&a);
michael@0:     return 1;
michael@0:   }
michael@0: 
michael@0:   {
michael@0:     char  *buf;
michael@0:     int    len;
michael@0: 
michael@0:     len = mp_radix_size(&a, 10);
michael@0:     buf = malloc(len);
michael@0:     mp_todecimal(&a, buf);
michael@0: 
michael@0:     puts(buf);
michael@0: 
michael@0:     free(buf);
michael@0:   }
michael@0: 
michael@0:   mp_clear(&a);
michael@0:   return 0;
michael@0: }
michael@0: 
michael@0: mp_err mp_fact(mp_int *a, mp_int *b)
michael@0: {
michael@0:   mp_int    ix, s;
michael@0:   mp_err    res = MP_OKAY;
michael@0: 
michael@0:   if(mp_cmp_z(a) < 0)
michael@0:     return MP_UNDEF;
michael@0: 
michael@0:   mp_init(&s);
michael@0:   mp_add_d(&s, 1, &s);   /* s = 1  */
michael@0:   mp_init(&ix);
michael@0:   mp_add_d(&ix, 1, &ix); /* ix = 1 */
michael@0: 
michael@0:   for(/*  */; mp_cmp(&ix, a) <= 0; mp_add_d(&ix, 1, &ix)) {
michael@0:     if((res = mp_mul(&s, &ix, &s)) != MP_OKAY)
michael@0:       break;
michael@0:   }
michael@0: 
michael@0:   mp_clear(&ix);
michael@0: 
michael@0:   /* Copy out results if we got them */
michael@0:   if(res == MP_OKAY)
michael@0:     mp_copy(&s, b);
michael@0: 
michael@0:   mp_clear(&s);
michael@0: 
michael@0:   return res;
michael@0: }