1 /* sub.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. (LICENSE)
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 "bcmath.h"
33 #include "private.h"
34 #include <stddef.h>
35 #include <stdbool.h>
36 #include <string.h>
37
38 /* Here is the full subtract routine that takes care of negative numbers.
39 N2 is subtracted from N1 and the result placed in RESULT. SCALE_MIN
40 is the minimum scale for the result. */
41
bc_sub(bc_num n1,bc_num n2,size_t scale_min)42 bc_num bc_sub(bc_num n1, bc_num n2, size_t scale_min)
43 {
44 bc_num diff = NULL;
45
46 if (n1->n_sign != n2->n_sign) {
47 diff = _bc_do_add(n1, n2);
48 diff->n_sign = n1->n_sign;
49 } else {
50 /* subtraction must be done. */
51 /* Compare magnitudes. */
52 switch (_bc_do_compare(n1, n2, scale_min, false)) {
53 case BCMATH_RIGHT_GREATER:
54 /* n1 is less than n2, subtract n1 from n2. */
55 diff = _bc_do_sub(n2, n1);
56 diff->n_sign = (n2->n_sign == PLUS ? MINUS : PLUS);
57 break;
58 case BCMATH_EQUAL: {
59 /* They are equal! return zero! */
60 size_t res_scale = MAX (scale_min, MAX(n1->n_scale, n2->n_scale));
61 diff = bc_new_num (1, res_scale);
62 break;
63 }
64 case BCMATH_LEFT_GREATER:
65 /* n2 is less than n1, subtract n2 from n1. */
66 diff = _bc_do_sub(n1, n2);
67 diff->n_sign = n1->n_sign;
68 break;
69 }
70 }
71
72 return diff;
73 }
74
