73 lines
2.1 KiB
C
73 lines
2.1 KiB
C
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/* mpz_invert (inv, x, n). Find multiplicative inverse of X in Z(N).
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If X has an inverse, return non-zero and store inverse in INVERSE,
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otherwise, return 0 and put garbage in INVERSE.
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Copyright 1996, 1997, 1998, 1999, 2000, 2001, 2005 Free Software Foundation,
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Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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int
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mpz_invert (mpz_ptr inverse, mpz_srcptr x, mpz_srcptr n)
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{
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mpz_t gcd, tmp;
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mp_size_t xsize, nsize, size;
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TMP_DECL;
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xsize = SIZ (x);
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nsize = SIZ (n);
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xsize = ABS (xsize);
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nsize = ABS (nsize);
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size = MAX (xsize, nsize) + 1;
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/* No inverse exists if the leftside operand is 0. Likewise, no
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inverse exists if the mod operand is 1. */
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if (xsize == 0 || (nsize == 1 && (PTR (n))[0] == 1))
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return 0;
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TMP_MARK;
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MPZ_TMP_INIT (gcd, size);
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MPZ_TMP_INIT (tmp, size);
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mpz_gcdext (gcd, tmp, (mpz_ptr) 0, x, n);
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/* If no inverse existed, return with an indication of that. */
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if (SIZ (gcd) != 1 || PTR(gcd)[0] != 1)
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{
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TMP_FREE;
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return 0;
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}
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/* Make sure we return a positive inverse. */
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if (SIZ (tmp) < 0)
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{
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if (SIZ (n) < 0)
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mpz_sub (inverse, tmp, n);
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else
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mpz_add (inverse, tmp, n);
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}
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else
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mpz_set (inverse, tmp);
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TMP_FREE;
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return 1;
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}
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