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/*
Copyright (C) 2010, 2011 Sebastian Pancratz
This file is part of FLINT.
FLINT is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License (LGPL) as published
by the Free Software Foundation; either version 3 of the License, or
(at your option) any later version. See <https://www.gnu.org/licenses/>.
*/
#include "mpn_extras.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_mod.h"
#include "fmpz_mod_poly.h"
void fmpz_mod_poly_inv_series_f(fmpz_t f, fmpz_mod_poly_t Qinv,
const fmpz_mod_poly_t Q, slong n, const fmpz_mod_ctx_t ctx)
{
const fmpz *p = fmpz_mod_ctx_modulus(ctx);
fmpz_t cinv;
fmpz *Qcopy;
int Qalloc;
if (Q->length >= n)
{
Qcopy = Q->coeffs;
Qalloc = 0;
}
else
{
slong i;
Qcopy = (fmpz *) flint_malloc(n * sizeof(fmpz));
for (i = 0; i < Q->length; i++)
Qcopy[i] = Q->coeffs[i];
flint_mpn_zero((nn_ptr) Qcopy + i, n - i);
Qalloc = 1;
}
fmpz_init(cinv);
fmpz_gcdinv(f, cinv, Q->coeffs, p);
if (!fmpz_is_one(f))
goto cleanup;
if (Qinv != Q)
{
fmpz_mod_poly_fit_length(Qinv, n, ctx);
/*
TODO: _fmpz_mod_poly_inv_series no longer accepts a precomputed
inverse leading coefficient; add back a version that does this.
*/
/* _fmpz_mod_poly_inv_series(Qinv->coeffs, Qcopy, n, cinv, ctx); */
_fmpz_mod_poly_inv_series(Qinv->coeffs, Qcopy, n, n, ctx);
}
else
{
fmpz *t = _fmpz_vec_init(n);
/* _fmpz_mod_poly_inv_series(t, Qcopy, n, cinv, ctx); */
_fmpz_mod_poly_inv_series(Qinv->coeffs, Qcopy, n, n, ctx);
_fmpz_vec_clear(Qinv->coeffs, Qinv->alloc);
Qinv->coeffs = t;
Qinv->alloc = n;
Qinv->length = n;
}
_fmpz_mod_poly_set_length(Qinv, n);
_fmpz_mod_poly_normalise(Qinv);
cleanup:
if (Qalloc)
flint_free(Qcopy);
fmpz_clear(cinv);
}