| // SPDX-License-Identifier: GPL-2.0-or-later |

| /* mpi-sub-ui.c - Subtract an unsigned integer from an MPI. |

| * |

| * Copyright 1991, 1993, 1994, 1996, 1999-2002, 2004, 2012, 2013, 2015 |

| * Free Software Foundation, Inc. |

| * |

| * This file was based on the GNU MP Library source file: |

| * https://gmplib.org/repo/gmp-6.2/file/510b83519d1c/mpz/aors_ui.h |

| * |

| * The GNU MP Library is free software; you can redistribute it and/or modify |

| * it under the terms of either: |

| * |

| * * the GNU Lesser General Public License as published by the Free |

| * Software Foundation; either version 3 of the License, or (at your |

| * option) any later version. |

| * |

| * or |

| * |

| * * the GNU General Public License as published by the Free Software |

| * Foundation; either version 2 of the License, or (at your option) any |

| * later version. |

| * |

| * or both in parallel, as here. |

| * |

| * The GNU MP Library is distributed in the hope that it will be useful, but |

| * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |

| * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |

| * for more details. |

| * |

| * You should have received copies of the GNU General Public License and the |

| * GNU Lesser General Public License along with the GNU MP Library. If not, |

| * see https://www.gnu.org/licenses/. |

| */ |

| |

| #include "mpi-internal.h" |

| |

| int mpi_sub_ui(MPI w, MPI u, unsigned long vval) |

| { |

| if (u->nlimbs == 0) { |

| if (mpi_resize(w, 1) < 0) |

| return -ENOMEM; |

| w->d[0] = vval; |

| w->nlimbs = (vval != 0); |

| w->sign = (vval != 0); |

| return 0; |

| } |

| |

| /* If not space for W (and possible carry), increase space. */ |

| if (mpi_resize(w, u->nlimbs + 1)) |

| return -ENOMEM; |

| |

| if (u->sign) { |

| mpi_limb_t cy; |

| |

| cy = mpihelp_add_1(w->d, u->d, u->nlimbs, (mpi_limb_t) vval); |

| w->d[u->nlimbs] = cy; |

| w->nlimbs = u->nlimbs + cy; |

| w->sign = 1; |

| } else { |

| /* The signs are different. Need exact comparison to determine |

| * which operand to subtract from which. |

| */ |

| if (u->nlimbs == 1 && u->d[0] < vval) { |

| w->d[0] = vval - u->d[0]; |

| w->nlimbs = 1; |

| w->sign = 1; |

| } else { |

| mpihelp_sub_1(w->d, u->d, u->nlimbs, (mpi_limb_t) vval); |

| /* Size can decrease with at most one limb. */ |

| w->nlimbs = (u->nlimbs - (w->d[u->nlimbs - 1] == 0)); |

| w->sign = 0; |

| } |

| } |

| |

| mpi_normalize(w); |

| return 0; |

| } |

| EXPORT_SYMBOL_GPL(mpi_sub_ui); |