pqc/external/flint-2.4.3/fmpz_mod_poly/gcdinv.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_vec.h"
#include "fmpz_mod_poly.h"
slong _fmpz_mod_poly_gcdinv(fmpz *G, fmpz *S,
const fmpz *A, slong lenA, const fmpz *B, slong lenB,
const fmpz_t p)
{
fmpz *T;
fmpz_t inv;
slong ans;
T = _fmpz_vec_init(lenA - 1);
fmpz_init(inv);
fmpz_invmod(inv, A + (lenA - 1), p);
ans = _fmpz_mod_poly_xgcd(G, T, S, B, lenB, A, lenA, inv, p);
fmpz_clear(inv);
_fmpz_vec_clear(T, lenA - 1);
return ans;
}
void fmpz_mod_poly_gcdinv(fmpz_mod_poly_t G, fmpz_mod_poly_t S,
const fmpz_mod_poly_t A, const fmpz_mod_poly_t B)
{
const slong lenA = A->length, lenB = B->length;
if (lenB < 2)
{
flint_printf("Exception (fmpz_mod_poly_gcdinv). lenB < 2.\n");
abort();
}
if (lenA >= lenB)
{
fmpz_mod_poly_t T;
fmpz_mod_poly_init(T, &A->p);
fmpz_mod_poly_rem(T, A, B);
fmpz_mod_poly_gcdinv(G, S, T, B);
fmpz_mod_poly_clear(T);
return;
}
if (lenA == 0)
{
fmpz_mod_poly_zero(G);
fmpz_mod_poly_zero(S);
}
else
{
fmpz *g, *s;
slong lenG;
if (G == A || G == B)
{
g = _fmpz_vec_init(lenA);
}
else
{
fmpz_mod_poly_fit_length(G, lenA);
g = G->coeffs;
}
if (S == A || S == B)
{
s = _fmpz_vec_init(lenB - 1);
}
else
{
fmpz_mod_poly_fit_length(S, lenB - 1);
s = S->coeffs;
}
lenG = _fmpz_mod_poly_gcdinv(g, s,
A->coeffs, lenA, B->coeffs, lenB, &A->p);
if (G == A || G == B)
{
_fmpz_vec_clear(G->coeffs, G->alloc);
G->coeffs = g;
G->alloc = lenA;
}
if (S == A || S == B)
{
_fmpz_vec_clear(S->coeffs, S->alloc);
S->coeffs = s;
S->alloc = lenB - 1;
}
_fmpz_mod_poly_set_length(G, lenG);
_fmpz_mod_poly_set_length(S, lenB - lenG);
_fmpz_mod_poly_normalise(S);
if (!fmpz_is_one(fmpz_mod_poly_lead(G)))
{
fmpz_t inv;
fmpz_init(inv);
fmpz_invmod(inv, fmpz_mod_poly_lead(G), &A->p);
fmpz_mod_poly_scalar_mul_fmpz(G, G, inv);
fmpz_mod_poly_scalar_mul_fmpz(S, S, inv);
fmpz_clear(inv);
}
}
}