github.com/aergoio/aergo@v1.3.1/libtool/src/gmp-6.1.2/mpz/invert.c (about)

     1  /* mpz_invert (inv, x, n).  Find multiplicative inverse of X in Z(N).
     2     If X has an inverse, return non-zero and store inverse in INVERSE,
     3     otherwise, return 0 and put garbage in INVERSE.
     4  
     5  Copyright 1996-2001, 2005, 2012, 2014 Free Software Foundation, Inc.
     6  
     7  This file is part of the GNU MP Library.
     8  
     9  The GNU MP Library is free software; you can redistribute it and/or modify
    10  it under the terms of either:
    11  
    12    * the GNU Lesser General Public License as published by the Free
    13      Software Foundation; either version 3 of the License, or (at your
    14      option) any later version.
    15  
    16  or
    17  
    18    * the GNU General Public License as published by the Free Software
    19      Foundation; either version 2 of the License, or (at your option) any
    20      later version.
    21  
    22  or both in parallel, as here.
    23  
    24  The GNU MP Library is distributed in the hope that it will be useful, but
    25  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    26  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    27  for more details.
    28  
    29  You should have received copies of the GNU General Public License and the
    30  GNU Lesser General Public License along with the GNU MP Library.  If not,
    31  see https://www.gnu.org/licenses/.  */
    32  
    33  #include "gmp.h"
    34  #include "gmp-impl.h"
    35  
    36  int
    37  mpz_invert (mpz_ptr inverse, mpz_srcptr x, mpz_srcptr n)
    38  {
    39    mpz_t gcd, tmp;
    40    mp_size_t xsize, nsize, size;
    41    TMP_DECL;
    42  
    43    xsize = ABSIZ (x);
    44    nsize = ABSIZ (n);
    45  
    46    size = MAX (xsize, nsize) + 1;
    47    TMP_MARK;
    48  
    49    MPZ_TMP_INIT (gcd, size);
    50    MPZ_TMP_INIT (tmp, size);
    51    mpz_gcdext (gcd, tmp, (mpz_ptr) 0, x, n);
    52  
    53    /* If no inverse existed, return with an indication of that.  */
    54    if (!MPZ_EQUAL_1_P (gcd))
    55      {
    56        TMP_FREE;
    57        return 0;
    58      }
    59  
    60    /* Make sure we return a positive inverse.  */
    61    if (SIZ (tmp) < 0)
    62      {
    63        if (SIZ (n) < 0)
    64  	mpz_sub (inverse, tmp, n);
    65        else
    66  	mpz_add (inverse, tmp, n);
    67      }
    68    else
    69      mpz_set (inverse, tmp);
    70  
    71    TMP_FREE;
    72    return 1;
    73  }