79 строки
2.3 KiB
C
79 строки
2.3 KiB
C
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// 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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