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
bc_raisemod(bc_num base,bc_num expo,bc_num mod,bc_num * result,int scale)46 bc_raisemod (bc_num base, bc_num expo, bc_num mod, bc_num *result, int scale)
47 {
48 bc_num power, exponent, modulus, 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 modulus = bc_copy_num (mod);
59 temp = bc_copy_num (BCG(_one_));
60 bc_init_num(&parity);
61
62 /* Check the base for scale digits. */
63 if (power->n_scale != 0)
64 {
65 bc_rt_warn ("non-zero scale in base");
66 bc_divide (power, BCG(_one_), &power, 0); /*truncate */
67 }
68
69 /* Check the exponent for scale digits. */
70 if (exponent->n_scale != 0)
71 {
72 bc_rt_warn ("non-zero scale in exponent");
73 bc_divide (exponent, BCG(_one_), &exponent, 0); /*truncate */
74 }
75
76 /* Check the modulus for scale digits. */
77 if (modulus->n_scale != 0)
78 {
79 bc_rt_warn ("non-zero scale in modulus");
80 bc_divide (modulus, BCG(_one_), &modulus, 0); /*truncate */
81 }
82
83 /* Do the calculation. */
84 rscale = MAX(scale, power->n_scale);
85 if ( !bc_compare(modulus, BCG(_one_)) )
86 {
87 temp = bc_new_num (1, scale);
88 }
89 else
90 {
91 while ( !bc_is_zero(exponent) )
92 {
93 (void) bc_divmod (exponent, BCG(_two_), &exponent, &parity, 0);
94 if ( !bc_is_zero(parity) )
95 {
96 bc_multiply (temp, power, &temp, rscale);
97 (void) bc_modulo (temp, modulus, &temp, scale);
98 }
99
100 bc_multiply (power, power, &power, rscale);
101 (void) bc_modulo (power, modulus, &power, scale);
102 }
103 }
104
105 /* Assign the value. */
106 bc_free_num (&power);
107 bc_free_num (&exponent);
108 bc_free_num (&modulus);
109 bc_free_num (result);
110 bc_free_num (&parity);
111 *result = temp;
112 return 0; /* Everything is OK. */
113 }
114
