pqc/external/flint-2.4.3/fmpz_poly/bound_roots.c
2014-05-24 23:16:06 +02:00

88 lines
2.3 KiB
C

/*=============================================================================
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) 2012 Fredrik Johansson
******************************************************************************/
#include "fmpz_poly.h"
/* quotient of absolute value, rounded up */
static __inline__ void
fmpz_cdiv_abs_q(fmpz_t q, const fmpz_t x, const fmpz_t y)
{
if (fmpz_sgn(x) == fmpz_sgn(y))
{
fmpz_cdiv_q(q, x, y);
}
else
{
fmpz_fdiv_q(q, x, y);
fmpz_neg(q, q);
}
}
void
_fmpz_poly_bound_roots(fmpz_t bound, const fmpz * poly, slong len)
{
if (len <= 1)
{
fmpz_zero(bound);
}
else if (len == 2)
{
fmpz_cdiv_abs_q(bound, poly + 0, poly + 1);
}
else
{
slong i;
fmpz_t t;
fmpz_init(t);
fmpz_mul_2exp(t, poly + len - 1, 1);
fmpz_cdiv_abs_q(bound, poly + 0, t);
fmpz_root(bound, bound, len - 1);
for (i = 1; i < len - 1; i++)
{
fmpz_cdiv_abs_q(t, poly + len - i - 1, poly + len - 1);
fmpz_root(t, t, i);
fmpz_add_ui(t, t, 1);
if (fmpz_cmp(t, bound) > 0)
fmpz_swap(t, bound);
}
fmpz_mul_2exp(bound, bound, 1);
fmpz_clear(t);
}
}
void
fmpz_poly_bound_roots(fmpz_t bound, const fmpz_poly_t poly)
{
_fmpz_poly_bound_roots(bound, poly->coeffs, poly->length);
}