| Marcelo Henrique Cerri | 4278e9d | 2020-07-20 19:08:09 +0200 | [diff] [blame] | 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); |