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78 lines
2.3 KiB
78 lines
2.3 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* mpi-sub-ui.c - Subtract an unsigned integer from an MPI. |
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* |
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* Copyright 1991, 1993, 1994, 1996, 1999-2002, 2004, 2012, 2013, 2015 |
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* Free Software Foundation, Inc. |
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* |
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* This file was based on the GNU MP Library source file: |
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* https://gmplib.org/repo/gmp-6.2/file/510b83519d1c/mpz/aors_ui.h |
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* |
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* The GNU MP Library is free software; you can redistribute it and/or modify |
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* it under the terms of either: |
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* |
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* * the GNU Lesser General Public License as published by the Free |
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* Software Foundation; either version 3 of the License, or (at your |
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* option) any later version. |
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* |
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* or |
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* |
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* * the GNU General Public License as published by the Free Software |
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* Foundation; either version 2 of the License, or (at your option) any |
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* later version. |
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* |
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* or both in parallel, as here. |
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* |
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* The GNU MP Library is distributed in the hope that it will be useful, but |
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* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* for more details. |
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* |
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* You should have received copies of the GNU General Public License and the |
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* GNU Lesser General Public License along with the GNU MP Library. If not, |
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* see https://www.gnu.org/licenses/. |
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*/ |
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#include "mpi-internal.h" |
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int mpi_sub_ui(MPI w, MPI u, unsigned long vval) |
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{ |
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if (u->nlimbs == 0) { |
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if (mpi_resize(w, 1) < 0) |
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return -ENOMEM; |
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w->d[0] = vval; |
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w->nlimbs = (vval != 0); |
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w->sign = (vval != 0); |
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return 0; |
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} |
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/* If not space for W (and possible carry), increase space. */ |
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if (mpi_resize(w, u->nlimbs + 1)) |
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return -ENOMEM; |
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if (u->sign) { |
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mpi_limb_t cy; |
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cy = mpihelp_add_1(w->d, u->d, u->nlimbs, (mpi_limb_t) vval); |
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w->d[u->nlimbs] = cy; |
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w->nlimbs = u->nlimbs + cy; |
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w->sign = 1; |
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} else { |
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/* The signs are different. Need exact comparison to determine |
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* which operand to subtract from which. |
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*/ |
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if (u->nlimbs == 1 && u->d[0] < vval) { |
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w->d[0] = vval - u->d[0]; |
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w->nlimbs = 1; |
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w->sign = 1; |
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} else { |
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mpihelp_sub_1(w->d, u->d, u->nlimbs, (mpi_limb_t) vval); |
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/* Size can decrease with at most one limb. */ |
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w->nlimbs = (u->nlimbs - (w->d[u->nlimbs - 1] == 0)); |
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w->sign = 0; |
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} |
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} |
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mpi_normalize(w); |
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return 0; |
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} |
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EXPORT_SYMBOL_GPL(mpi_sub_ui);
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