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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 "mpi-internal.h" | |
36 | ||
37 | int mpi_sub_ui(MPI w, MPI u, unsigned long vval) | |
38 | { | |
39 | if (u->nlimbs == 0) { | |
40 | if (mpi_resize(w, 1) < 0) | |
41 | return -ENOMEM; | |
42 | w->d[0] = vval; | |
43 | w->nlimbs = (vval != 0); | |
44 | w->sign = (vval != 0); | |
45 | return 0; | |
46 | } | |
47 | ||
48 | /* If not space for W (and possible carry), increase space. */ | |
49 | if (mpi_resize(w, u->nlimbs + 1)) | |
50 | return -ENOMEM; | |
51 | ||
52 | if (u->sign) { | |
53 | mpi_limb_t cy; | |
54 | ||
55 | cy = mpihelp_add_1(w->d, u->d, u->nlimbs, (mpi_limb_t) vval); | |
56 | w->d[u->nlimbs] = cy; | |
57 | w->nlimbs = u->nlimbs + cy; | |
58 | w->sign = 1; | |
59 | } else { | |
60 | /* The signs are different. Need exact comparison to determine | |
61 | * which operand to subtract from which. | |
62 | */ | |
63 | if (u->nlimbs == 1 && u->d[0] < vval) { | |
64 | w->d[0] = vval - u->d[0]; | |
65 | w->nlimbs = 1; | |
66 | w->sign = 1; | |
67 | } else { | |
68 | mpihelp_sub_1(w->d, u->d, u->nlimbs, (mpi_limb_t) vval); | |
69 | /* Size can decrease with at most one limb. */ | |
70 | w->nlimbs = (u->nlimbs - (w->d[u->nlimbs - 1] == 0)); | |
71 | w->sign = 0; | |
72 | } | |
73 | } | |
74 | ||
75 | mpi_normalize(w); | |
76 | return 0; | |
77 | } | |
78 | EXPORT_SYMBOL_GPL(mpi_sub_ui); |