1// SPDX-License-Identifier: GPL-2.0-or-later
2/* mpi-sub-ui.c - Subtract an unsigned integer from an MPI.
3 *
4 * Copyright 1991, 1993, 1994, 1996, 1999-2002, 2004, 2012, 2013, 2015
5 * Free Software Foundation, Inc.
6 *
7 * This file was based on the GNU MP Library source file:
8 * https://gmplib.org/repo/gmp-6.2/file/510b83519d1c/mpz/aors_ui.h
9 *
10 * The GNU MP Library is free software; you can redistribute it and/or modify
11 * it under the terms of either:
12 *
13 * * the GNU Lesser General Public License as published by the Free
14 * Software Foundation; either version 3 of the License, or (at your
15 * option) any later version.
16 *
17 * or
18 *
19 * * the GNU General Public License as published by the Free Software
20 * Foundation; either version 2 of the License, or (at your option) any
21 * later version.
22 *
23 * or both in parallel, as here.
24 *
25 * The GNU MP Library is distributed in the hope that it will be useful, but
26 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
27 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
28 * for more details.
29 *
30 * You should have received copies of the GNU General Public License and the
31 * GNU Lesser General Public License along with the GNU MP Library. If not,
32 * see https://www.gnu.org/licenses/.
33 */
34
35#include <linux/export.h>
36
37#include "mpi-internal.h"
38
39int mpi_sub_ui(MPI w, MPI u, unsigned long vval)
40{
41 if (u->nlimbs == 0) {
42 if (mpi_resize(a: w, nlimbs: 1) < 0)
43 return -ENOMEM;
44 w->d[0] = vval;
45 w->nlimbs = (vval != 0);
46 w->sign = (vval != 0);
47 return 0;
48 }
49
50 /* If not space for W (and possible carry), increase space. */
51 if (mpi_resize(a: w, nlimbs: u->nlimbs + 1))
52 return -ENOMEM;
53
54 if (u->sign) {
55 mpi_limb_t cy;
56
57 cy = mpihelp_add_1(res_ptr: w->d, s1_ptr: u->d, s1_size: u->nlimbs, s2_limb: (mpi_limb_t) vval);
58 w->d[u->nlimbs] = cy;
59 w->nlimbs = u->nlimbs + cy;
60 w->sign = 1;
61 } else {
62 /* The signs are different. Need exact comparison to determine
63 * which operand to subtract from which.
64 */
65 if (u->nlimbs == 1 && u->d[0] < vval) {
66 w->d[0] = vval - u->d[0];
67 w->nlimbs = 1;
68 w->sign = 1;
69 } else {
70 mpihelp_sub_1(res_ptr: w->d, s1_ptr: u->d, s1_size: u->nlimbs, s2_limb: (mpi_limb_t) vval);
71 /* Size can decrease with at most one limb. */
72 w->nlimbs = (u->nlimbs - (w->d[u->nlimbs - 1] == 0));
73 w->sign = 0;
74 }
75 }
76
77 mpi_normalize(a: w);
78 return 0;
79}
80EXPORT_SYMBOL_GPL(mpi_sub_ui);
81