Coverage Report

Created: 2024-11-21 07:03

/src/libgmp/mpz/invert.c
Line
Count
Source (jump to first uncovered line)
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-impl.h"
34
35
int
36
mpz_invert (mpz_ptr inverse, mpz_srcptr x, mpz_srcptr n)
37
1.58k
{
38
1.58k
  mpz_t gcd, tmp;
39
1.58k
  mp_size_t xsize, nsize, size;
40
1.58k
  TMP_DECL;
41
42
1.58k
  xsize = ABSIZ (x);
43
1.58k
  nsize = ABSIZ (n);
44
45
1.58k
  size = MAX (xsize, nsize) + 1;
46
1.58k
  TMP_MARK;
47
48
1.58k
  MPZ_TMP_INIT (gcd, size);
49
1.58k
  MPZ_TMP_INIT (tmp, size);
50
1.58k
  mpz_gcdext (gcd, tmp, (mpz_ptr) 0, x, n);
51
52
  /* If no inverse existed, return with an indication of that.  */
53
1.58k
  if (!MPZ_EQUAL_1_P (gcd))
54
559
    {
55
559
      TMP_FREE;
56
559
      return 0;
57
559
    }
58
59
  /* Make sure we return a positive inverse.  */
60
1.02k
  if (SIZ (tmp) < 0)
61
511
    {
62
511
      if (SIZ (n) < 0)
63
0
  mpz_sub (inverse, tmp, n);
64
511
      else
65
511
  mpz_add (inverse, tmp, n);
66
511
    }
67
513
  else
68
513
    mpz_set (inverse, tmp);
69
70
1.02k
  TMP_FREE;
71
1.02k
  return 1;
72
1.58k
}