pqc/external/flint-2.4.3/fmpz_mod_poly/powmod_ui_binexp.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) 2010 William Hart
Copyright (C) 2011 Fredrik Johansson
Copyright (C) 2012 Lina Kulakova
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "fmpz_vec.h"
#include "fmpz_mod_poly.h"
#include "ulong_extras.h"
void
_fmpz_mod_poly_powmod_ui_binexp(fmpz * res, const fmpz * poly,
ulong e, const fmpz * f, slong lenf, const fmpz_t p)
{
fmpz * T, * Q;
fmpz_t invf;
slong lenT, lenQ;
int i;
if (lenf == 2)
{
fmpz_powm_ui(res, poly, e, p);
return;
}
lenT = 2 * lenf - 3;
lenQ = FLINT_MAX(lenT - lenf + 1, 1);
T = _fmpz_vec_init(lenT + lenQ);
Q = T + lenT;
fmpz_init(invf);
fmpz_invmod(invf, f + lenf - 1, p);
_fmpz_vec_set(res, poly, lenf - 1);
for (i = ((int) FLINT_BIT_COUNT(e) - 2); i >= 0; i--)
{
_fmpz_mod_poly_sqr(T, res, lenf - 1, p);
_fmpz_mod_poly_divrem(Q, res, T, 2 * lenf - 3, f, lenf, invf, p);
if (e & (UWORD(1) << i))
{
_fmpz_mod_poly_mul(T, res, lenf - 1, poly, lenf - 1, p);
_fmpz_mod_poly_divrem(Q, res, T, 2 * lenf - 3, f, lenf, invf, p);
}
}
fmpz_clear(invf);
_fmpz_vec_clear(T, lenT + lenQ);
}
void
fmpz_mod_poly_powmod_ui_binexp(fmpz_mod_poly_t res,
const fmpz_mod_poly_t poly, ulong e,
const fmpz_mod_poly_t f)
{
fmpz * q;
slong len = poly->length;
slong lenf = f->length;
slong trunc = lenf - 1;
int qcopy = 0;
if (lenf == 0)
{
flint_printf("Exception (fmpz_mod_poly_powmod). Divide by zero\n");
abort();
}
if (len >= lenf)
{
fmpz_mod_poly_t t, r;
fmpz_mod_poly_init(t, &res->p);
fmpz_mod_poly_init(r, &res->p);
fmpz_mod_poly_divrem(t, r, poly, f);
fmpz_mod_poly_powmod_ui_binexp(res, r, e, f);
fmpz_mod_poly_clear(t);
fmpz_mod_poly_clear(r);
return;
}
if (e <= 2)
{
if (e == UWORD(0))
{
fmpz_mod_poly_fit_length(res, 1);
fmpz_one(res->coeffs);
_fmpz_mod_poly_set_length(res, 1);
}
else if (e == UWORD(1))
{
fmpz_mod_poly_set(res, poly);
}
else
fmpz_mod_poly_mulmod(res, poly, poly, f);
return;
}
if (lenf == 1 || len == 0)
{
fmpz_mod_poly_zero(res);
return;
}
if (len < trunc)
{
q = _fmpz_vec_init(trunc);
_fmpz_vec_set(q, poly->coeffs, len);
_fmpz_vec_zero(q + len, trunc - len);
qcopy = 1;
} else
q = poly->coeffs;
if ((res == poly && !qcopy) || (res == f))
{
fmpz_mod_poly_t t;
fmpz_mod_poly_init2(t, &poly->p, 2 * lenf - 3);
_fmpz_mod_poly_powmod_ui_binexp(t->coeffs,
q, e, f->coeffs, lenf, &poly->p);
fmpz_mod_poly_swap(res, t);
fmpz_mod_poly_clear(t);
}
else
{
fmpz_mod_poly_fit_length(res, 2 * lenf - 3);
_fmpz_mod_poly_powmod_ui_binexp(res->coeffs,
q, e, f->coeffs, lenf, &poly->p);
}
if (qcopy)
_fmpz_vec_clear(q, trunc);
_fmpz_mod_poly_set_length(res, trunc);
_fmpz_mod_poly_normalise(res);
}