pqc/external/flint-2.4.3/fmpq_poly/revert_series_lagrange.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) 2010 Sebastian Pancratz
Copyright (C) 2011 Fredrik Johansson
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_poly.h"
#include "fmpq_poly.h"
static void
_set_vec(fmpz * rnum, fmpz_t den,
const fmpz * xnum, const fmpz * xden, slong len)
{
slong j;
fmpz_t t;
fmpz_init(t);
fmpz_one(den);
for (j = 0; j < len; j++)
fmpz_lcm(den, den, xden + j);
for (j = 0; j < len; j++)
{
fmpz_divexact(t, den, xden + j);
fmpz_mul(rnum + j, xnum + j, t);
}
fmpz_clear(t);
}
void
_fmpq_poly_revert_series_lagrange(fmpz * Qinv, fmpz_t den,
const fmpz * Q, const fmpz_t Qden, slong n)
{
slong i;
fmpz *R, *S, *T, *dens, *tmp;
fmpz_t Rden, Sden, Tden;
if (fmpz_is_one(Qden) && (n > 1) && fmpz_is_pm1(Q + 1))
{
_fmpz_poly_revert_series(Qinv, Q, n);
fmpz_one(den);
}
else if (n <= 2)
{
fmpz_zero(Qinv);
if (n == 2)
{
fmpz_set(Qinv + 1, Qden);
fmpz_set(den, Q + 1);
_fmpq_poly_canonicalise(Qinv, den, 2);
}
}
else
{
dens = _fmpz_vec_init(n);
R = _fmpz_vec_init(n - 1);
S = _fmpz_vec_init(n - 1);
T = _fmpz_vec_init(n - 1);
fmpz_init(Rden);
fmpz_init(Sden);
fmpz_init(Tden);
fmpz_zero(Qinv);
fmpz_one(dens);
fmpz_set(Qinv + 1, Qden);
fmpz_set(dens + 1, Q + 1);
_fmpq_poly_inv_series(R, Rden, Q + 1, Qden, n - 1);
_fmpq_poly_canonicalise(R, Rden, n - 1);
_fmpz_vec_set(S, R, n - 1);
fmpz_set(Sden, Rden);
for (i = 2; i < n; i++)
{
_fmpq_poly_mullow(T, Tden, S, Sden, n - 1, R, Rden, n - 1, n - 1);
_fmpq_poly_canonicalise(T, Tden, n - 1);
fmpz_set(Qinv + i, T + i - 1);
fmpz_mul_ui(dens + i, Tden, i);
tmp = S; S = T; T = tmp;
fmpz_swap(Sden, Tden);
}
_set_vec(Qinv, den, Qinv, dens, n);
_fmpq_poly_canonicalise(Qinv, den, n);
_fmpz_vec_clear(R, n - 1);
_fmpz_vec_clear(S, n - 1);
_fmpz_vec_clear(T, n - 1);
_fmpz_vec_clear(dens, n);
fmpz_clear(Rden);
fmpz_clear(Sden);
fmpz_clear(Tden);
}
}
void
fmpq_poly_revert_series_lagrange(fmpq_poly_t res,
const fmpq_poly_t poly, slong n)
{
fmpz *copy;
int alloc;
if (poly->length < 2 || !fmpz_is_zero(poly->coeffs)
|| fmpz_is_zero(poly->coeffs + 1))
{
flint_printf("Exception (fmpq_poly_revert_series_lagrange). Input must have \n"
"zero constant term and nonzero coefficient of x^1.\n");
abort();
}
if (n < 2)
{
fmpq_poly_zero(res);
return;
}
if (poly->length >= n)
{
copy = poly->coeffs;
alloc = 0;
}
else
{
slong i;
copy = (fmpz *) flint_malloc(n * sizeof(fmpz));
for (i = 0; i < poly->length; i++)
copy[i] = poly->coeffs[i];
for ( ; i < n; i++)
copy[i] = 0;
alloc = 1;
}
if (res != poly)
{
fmpq_poly_fit_length(res, n);
_fmpq_poly_revert_series_lagrange(res->coeffs,
res->den, copy, poly->den, n);
}
else
{
fmpq_poly_t t;
fmpq_poly_init2(t, n);
_fmpq_poly_revert_series_lagrange(t->coeffs,
t->den, copy, poly->den, n);
fmpq_poly_swap(res, t);
fmpq_poly_clear(t);
}
_fmpq_poly_set_length(res, n);
_fmpq_poly_normalise(res);
if (alloc)
flint_free(copy);
}