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/* 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 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 Library General Public License as published by
the Free Software Foundation; either version 2 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 Library General Public
License for more details.
You should have received a copy of the GNU Library 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;
}
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