mirror of https://github.com/macssh/macssh.git
78 lines
2.1 KiB
C
Executable File
78 lines
2.1 KiB
C
Executable File
/* mpz_invert (inv, x, n). Find multiplicative inverse of X in Z(N).
|
|
If X has an inverse, return non-zero and store inverse in INVERSE,
|
|
otherwise, return 0 and put garbage in INVERSE.
|
|
|
|
Copyright (C) 1996, 1997, 1998, 1999, 2000 Free Software Foundation, Inc.
|
|
|
|
This file is part of the GNU MP Library.
|
|
|
|
The GNU MP Library is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU Lesser General Public License as published by
|
|
the Free Software Foundation; either version 2.1 of the License, or (at your
|
|
option) any later version.
|
|
|
|
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 Lesser General Public
|
|
License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public License
|
|
along with the GNU MP Library; see the file COPYING.LIB. If not, write to
|
|
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
|
|
MA 02111-1307, USA. */
|
|
|
|
#include "gmp.h"
|
|
#include "gmp-impl.h"
|
|
|
|
int
|
|
#if __STDC__
|
|
mpz_invert (mpz_ptr inverse, mpz_srcptr x, mpz_srcptr n)
|
|
#else
|
|
mpz_invert (inverse, x, n)
|
|
mpz_ptr inverse;
|
|
mpz_srcptr x, n;
|
|
#endif
|
|
{
|
|
mpz_t gcd, tmp;
|
|
mp_size_t xsize, nsize, size;
|
|
TMP_DECL (marker);
|
|
|
|
xsize = SIZ (x);
|
|
nsize = SIZ (n);
|
|
xsize = ABS (xsize);
|
|
nsize = ABS (nsize);
|
|
size = MAX (xsize, nsize) + 1;
|
|
|
|
/* No inverse exists if the leftside operand is 0. Likewise, no
|
|
inverse exists if the mod operand is 1. */
|
|
if (xsize == 0 || (nsize == 1 && (PTR (n))[0] == 1))
|
|
return 0;
|
|
|
|
TMP_MARK (marker);
|
|
|
|
MPZ_TMP_INIT (gcd, size);
|
|
MPZ_TMP_INIT (tmp, size);
|
|
mpz_gcdext (gcd, tmp, (mpz_ptr) 0, x, n);
|
|
|
|
/* If no inverse existed, return with an indication of that. */
|
|
if (gcd->_mp_size != 1 || (gcd->_mp_d)[0] != 1)
|
|
{
|
|
TMP_FREE (marker);
|
|
return 0;
|
|
}
|
|
|
|
/* Make sure we return a positive inverse. */
|
|
if (SIZ (tmp) < 0)
|
|
{
|
|
if (SIZ (n) < 0)
|
|
mpz_sub (inverse, tmp, n);
|
|
else
|
|
mpz_add (inverse, tmp, n);
|
|
}
|
|
else
|
|
mpz_set (inverse, tmp);
|
|
|
|
TMP_FREE (marker);
|
|
return 1;
|
|
}
|