1 /* raise.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
42 /* Raise NUM1 to the NUM2 power. The result is placed in RESULT.
43 Maximum exponent is LONG_MAX. If a NUM2 is not an integer,
44 only the integer part is used. */
45
46 void
47 bc_raise (bc_num num1, bc_num num2, bc_num *result, int scale)
48 {
49 bc_num temp, power;
50 long exponent;
51 int rscale;
52 int pwrscale;
53 int calcscale;
54 char neg;
55
56 /* Check the exponent for scale digits and convert to a long. */
57 if (num2->n_scale != 0)
58 bc_rt_warn ("non-zero scale in exponent");
59 exponent = bc_num2long (num2);
60 if (exponent == 0 && (num2->n_len > 1 || num2->n_value[0] != 0))
61 bc_rt_error ("exponent too large in raise");
62
63 /* Special case if exponent is a zero. */
64 if (exponent == 0)
65 {
66 bc_free_num (result);
67 *result = bc_copy_num (BCG(_one_));
68 return;
69 }
70
71 /* Other initializations. */
72 if (exponent < 0)
73 {
74 neg = TRUE;
75 exponent = -exponent;
76 rscale = scale;
77 }
78 else
79 {
80 neg = FALSE;
81 rscale = MIN (num1->n_scale*exponent, MAX(scale, num1->n_scale));
82 }
83
84 /* Set initial value of temp. */
85 power = bc_copy_num (num1);
86 pwrscale = num1->n_scale;
87 while ((exponent & 1) == 0)
88 {
89 pwrscale = 2*pwrscale;
90 bc_multiply (power, power, &power, pwrscale);
91 exponent = exponent >> 1;
92 }
93 temp = bc_copy_num (power);
94 calcscale = pwrscale;
95 exponent = exponent >> 1;
96
97 /* Do the calculation. */
98 while (exponent > 0)
99 {
100 pwrscale = 2*pwrscale;
101 bc_multiply (power, power, &power, pwrscale);
102 if ((exponent & 1) == 1) {
103 calcscale = pwrscale + calcscale;
104 bc_multiply (temp, power, &temp, calcscale);
105 }
106 exponent = exponent >> 1;
107 }
108
109 /* Assign the value. */
110 if (neg)
111 {
112 bc_divide (BCG(_one_), temp, result, rscale);
113 bc_free_num (&temp);
114 }
115 else
116 {
117 bc_free_num (result);
118 *result = temp;
119 if ((*result)->n_scale > rscale)
120 (*result)->n_scale = rscale;
121 }
122 bc_free_num (&power);
123 }
124