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

124 lines
3.2 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) 2010 Sebastian Pancratz
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"
void
_fmpz_poly_pow_binomial(fmpz * res, const fmpz * poly, ulong e)
{
ulong i, f;
fmpz_t a, b, c;
*a = WORD(1);
*b = WORD(1);
*c = WORD(1);
fmpz_one(res);
fmpz_one(res + e);
for (i = UWORD(1), f = e - UWORD(1); i <= (e - UWORD(1)) >> 1; i++, f--)
{
fmpz_mul(a, a, poly);
fmpz_mul(b, b, poly + 1);
fmpz_mul_ui(c, c, f + UWORD(1));
fmpz_divexact_ui(c, c, i);
fmpz_mul(res + i, b, c);
fmpz_mul(res + f, a, c);
}
if ((e & UWORD(1)) == UWORD(0))
{
fmpz_mul(a, a, poly);
fmpz_mul(b, b, poly + 1);
fmpz_mul_ui(c, c, f + UWORD(1));
fmpz_divexact_ui(c, c, i);
fmpz_mul(res + i, b, c);
fmpz_mul(res + i, res + i, a);
i++, f--;
}
for ( ; i <= e; i++, f--)
{
fmpz_mul(a, a, poly);
fmpz_mul(b, b, poly + 1);
fmpz_mul(res + i, res + i, b);
fmpz_mul(res + f, res + f, a);
}
fmpz_clear(a);
fmpz_clear(b);
fmpz_clear(c);
}
void
fmpz_poly_pow_binomial(fmpz_poly_t res, const fmpz_poly_t poly, ulong e)
{
const slong len = poly->length;
slong rlen;
if (len != 2)
{
flint_printf("Exception (fmpz_poly_pow_binomial). poly->length not equal to 2.\n");
abort();
}
if (e < UWORD(3))
{
if (e == UWORD(0))
fmpz_poly_set_ui(res, UWORD(1));
else if (e == UWORD(1))
fmpz_poly_set(res, poly);
else /* e == UWORD(2) */
fmpz_poly_sqr(res, poly);
return;
}
rlen = (slong) e + 1;
if (res != poly)
{
fmpz_poly_fit_length(res, rlen);
_fmpz_poly_set_length(res, rlen);
_fmpz_poly_pow_binomial(res->coeffs, poly->coeffs, e);
}
else
{
fmpz_poly_t t;
fmpz_poly_init2(t, rlen);
_fmpz_poly_set_length(t, rlen);
_fmpz_poly_pow_binomial(t->coeffs, poly->coeffs, e);
fmpz_poly_swap(res, t);
fmpz_poly_clear(t);
}
}