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fact.c
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00001 /*
00002  * fact.c
00003  *
00004  * Compute factorial of input integer
00005  *
00006  * ***** BEGIN LICENSE BLOCK *****
00007  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
00008  *
00009  * The contents of this file are subject to the Mozilla Public License Version
00010  * 1.1 (the "License"); you may not use this file except in compliance with
00011  * the License. You may obtain a copy of the License at
00012  * http://www.mozilla.org/MPL/
00013  *
00014  * Software distributed under the License is distributed on an "AS IS" basis,
00015  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
00016  * for the specific language governing rights and limitations under the
00017  * License.
00018  *
00019  * The Original Code is the MPI Arbitrary Precision Integer Arithmetic library.
00020  *
00021  * The Initial Developer of the Original Code is
00022  * Michael J. Fromberger.
00023  * Portions created by the Initial Developer are Copyright (C) 1998
00024  * the Initial Developer. All Rights Reserved.
00025  *
00026  * Contributor(s):
00027  *
00028  * Alternatively, the contents of this file may be used under the terms of
00029  * either the GNU General Public License Version 2 or later (the "GPL"), or
00030  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
00031  * in which case the provisions of the GPL or the LGPL are applicable instead
00032  * of those above. If you wish to allow use of your version of this file only
00033  * under the terms of either the GPL or the LGPL, and not to allow others to
00034  * use your version of this file under the terms of the MPL, indicate your
00035  * decision by deleting the provisions above and replace them with the notice
00036  * and other provisions required by the GPL or the LGPL. If you do not delete
00037  * the provisions above, a recipient may use your version of this file under
00038  * the terms of any one of the MPL, the GPL or the LGPL.
00039  *
00040  * ***** END LICENSE BLOCK ***** */
00041 /* $Id: fact.c,v 1.3 2004/04/27 23:04:37 gerv%gerv.net Exp $ */
00042 
00043 #include <stdio.h>
00044 #include <stdlib.h>
00045 #include <string.h>
00046 
00047 #include "mpi.h"
00048 
00049 mp_err mp_fact(mp_int *a, mp_int *b);
00050 
00051 int main(int argc, char *argv[])
00052 {
00053   mp_int  a;
00054   mp_err  res;
00055 
00056   if(argc < 2) {
00057     fprintf(stderr, "Usage: %s <number>\n", argv[0]);
00058     return 1;
00059   }
00060 
00061   mp_init(&a);
00062   mp_read_radix(&a, argv[1], 10);
00063 
00064   if((res = mp_fact(&a, &a)) != MP_OKAY) {
00065     fprintf(stderr, "%s: error: %s\n", argv[0],
00066            mp_strerror(res));
00067     mp_clear(&a);
00068     return 1;
00069   }
00070 
00071   {
00072     char  *buf;
00073     int    len;
00074 
00075     len = mp_radix_size(&a, 10);
00076     buf = malloc(len);
00077     mp_todecimal(&a, buf);
00078 
00079     puts(buf);
00080 
00081     free(buf);
00082   }
00083 
00084   mp_clear(&a);
00085   return 0;
00086 }
00087 
00088 mp_err mp_fact(mp_int *a, mp_int *b)
00089 {
00090   mp_int    ix, s;
00091   mp_err    res = MP_OKAY;
00092 
00093   if(mp_cmp_z(a) < 0)
00094     return MP_UNDEF;
00095 
00096   mp_init(&s);
00097   mp_add_d(&s, 1, &s);   /* s = 1  */
00098   mp_init(&ix);
00099   mp_add_d(&ix, 1, &ix); /* ix = 1 */
00100 
00101   for(/*  */; mp_cmp(&ix, a) <= 0; mp_add_d(&ix, 1, &ix)) {
00102     if((res = mp_mul(&s, &ix, &s)) != MP_OKAY)
00103       break;
00104   }
00105 
00106   mp_clear(&ix);
00107 
00108   /* Copy out results if we got them */
00109   if(res == MP_OKAY)
00110     mp_copy(&s, b);
00111 
00112   mp_clear(&s);
00113 
00114   return res;
00115 }