1 /* raisemod.c: bcmath library file. */
2 /*
3 Copyright (C) 1991, 1992, 1993, 1994, 1997 Free Software Foundation, Inc.
4 Copyright (C) 2000 Philip A. Nelson
5
6 This library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2 of the License, or (at your option) any later version.
10
11 This library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details. (COPYING.LIB)
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with this library; if not, write to:
18
19 The Free Software Foundation, Inc.
20 59 Temple Place, Suite 330
21 Boston, MA 02111-1307 USA.
22
23 You may contact the author by:
24 e-mail: philnelson@acm.org
25 us-mail: Philip A. Nelson
26 Computer Science Department, 9062
27 Western Washington University
28 Bellingham, WA 98226-9062
29
30 *************************************************************************/
31
32 #include <config.h>
33 #include <stdio.h>
34 #include <assert.h>
35 #include <stdlib.h>
36 #include <ctype.h>
37 #include <stdarg.h>
38 #include "bcmath.h"
39 #include "private.h"
40
41 /* Raise BASE to the EXPO power, reduced modulo MOD. The result is
42 placed in RESULT. If a EXPO is not an integer,
43 only the integer part is used. */
44
45 int
46 bc_raisemod (bc_num base, bc_num expo, bc_num mod, bc_num *result, int scale)
47 {
48 bc_num power, exponent, parity, temp;
49 int rscale;
50
51 /* Check for correct numbers. */
52 if (bc_is_zero(mod)) return -1;
53 if (bc_is_neg(expo)) return -1;
54
55 /* Set initial values. */
56 power = bc_copy_num (base);
57 exponent = bc_copy_num (expo);
58 temp = bc_copy_num (BCG(_one_));
59 bc_init_num(&parity);
60
61 /* Check the base for scale digits. */
62 if (base->n_scale != 0)
63 bc_rt_warn ("non-zero scale in base");
64
65 /* Check the exponent for scale digits. */
66 if (exponent->n_scale != 0)
67 {
68 bc_rt_warn ("non-zero scale in exponent");
69 bc_divide (exponent, BCG(_one_), &exponent, 0); /*truncate */
70 }
71
72 /* Check the modulus for scale digits. */
73 if (mod->n_scale != 0)
74 bc_rt_warn ("non-zero scale in modulus");
75
76 /* Do the calculation. */
77 rscale = MAX(scale, base->n_scale);
78 while ( !bc_is_zero(exponent) )
79 {
80 (void) bc_divmod (exponent, BCG(_two_), &exponent, &parity, 0);
81 if ( !bc_is_zero(parity) )
82 {
83 bc_multiply (temp, power, &temp, rscale);
84 (void) bc_modulo (temp, mod, &temp, scale);
85 }
86
87 bc_multiply (power, power, &power, rscale);
88 (void) bc_modulo (power, mod, &power, scale);
89 }
90
91 /* Assign the value. */
92 bc_free_num (&power);
93 bc_free_num (&exponent);
94 bc_free_num (result);
95 bc_free_num (&parity);
96 *result = temp;
97 return 0; /* Everything is OK. */
98 }