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1// SPDX-License-Identifier: GPL-2.0-or-later2/* mpi-sub-ui.c - Subtract an unsigned integer from an MPI.3 *4 * Copyright 1991, 1993, 1994, 1996, 1999-2002, 2004, 2012, 2013, 20155 * 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.h9 *10 * The GNU MP Library is free software; you can redistribute it and/or modify11 * it under the terms of either:12 *13 * * the GNU Lesser General Public License as published by the Free14 * Software Foundation; either version 3 of the License, or (at your15 * option) any later version.16 *17 * or18 *19 * * the GNU General Public License as published by the Free Software20 * Foundation; either version 2 of the License, or (at your option) any21 * 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, but26 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY27 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License28 * for more details.29 *30 * You should have received copies of the GNU General Public License and the31 * 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 37int 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 determine61 * 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}78EXPORT_SYMBOL_GPL(mpi_sub_ui);79