pqc/external/flint-2.4.3/fmpz_mod_poly/invmod.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
This file is part of FLINT.
FLINT is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
FLINT 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2011 William Hart
Copyright (C) 2012 Sebastian Pancratz
******************************************************************************/
#include <stdlib.h>
#include "fmpz_mod_poly.h"
int _fmpz_mod_poly_invmod(fmpz *A,
const fmpz *B, slong lenB,
const fmpz *P, slong lenP, const fmpz_t p)
{
fmpz *G;
slong lenG;
FMPZ_VEC_NORM(B, lenB);
G = _fmpz_vec_init(lenB);
lenG = _fmpz_mod_poly_gcdinv(G, A, B, lenB, P, lenP, p);
if (lenG == 1 && !fmpz_is_one(G + 0))
{
fmpz_t invG;
fmpz_init(invG);
fmpz_invmod(invG, G + 0, p);
_fmpz_mod_poly_scalar_mul_fmpz(A, A, lenP - 1, invG, p);
fmpz_clear(invG);
}
_fmpz_vec_clear(G, lenB);
return (lenG == 1);
}
int fmpz_mod_poly_invmod(fmpz_mod_poly_t A,
const fmpz_mod_poly_t B, const fmpz_mod_poly_t P)
{
const slong lenB = B->length, lenP = P->length;
fmpz *t;
int ans;
if (lenP < 2)
{
flint_printf("Exception (fmpz_mod_poly_invmod). lenP < 2.\n");
abort();
}
if (lenB == 0)
{
fmpz_mod_poly_zero(A);
return 0;
}
if (lenB >= lenP)
{
fmpz_mod_poly_t T;
fmpz_mod_poly_init(T, &B->p);
fmpz_mod_poly_rem(T, B, P);
ans = fmpz_mod_poly_invmod(A, T, P);
fmpz_mod_poly_clear(T);
return ans;
}
if (A != B && A != P)
{
fmpz_mod_poly_fit_length(A, lenP - 1);
t = A->coeffs;
}
else
{
t = _fmpz_vec_init(lenP);
}
ans = _fmpz_mod_poly_invmod(t, B->coeffs, lenB, P->coeffs, lenP, &B->p);
if (A == B || A == P)
{
_fmpz_vec_clear(A->coeffs, A->alloc);
A->coeffs = t;
A->alloc = lenP - 1;
}
_fmpz_mod_poly_set_length(A, lenP - 1);
_fmpz_mod_poly_normalise(A);
return ans;
}