linux-mm / kernel / git / torvalds / linux / cceb634774efca60f8cc57041234f00faf97f22d / . / lib / mpi / mpi-sub-ui.c

// 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); |