pqc/external/flint-2.4.3/fmpz/fdiv_r_2exp.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) 2009 William Hart
Copyright (C) 2011 Sebastian Pancratz
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "ulong_extras.h"
#include "fmpz.h"
void fmpz_fdiv_r_2exp(fmpz_t f, const fmpz_t g, ulong exp)
{
fmpz d = *g;
if (!COEFF_IS_MPZ(d)) /* g is small */
{
if (d >= 0)
{
fmpz_set_ui(f, exp < (FLINT_BITS - 2) ? d & ((WORD(1) << exp) - 1) : d);
}
else
{
if (exp <= FLINT_BITS - 2)
{
fmpz_set_ui(f, d & ((WORD(1) << exp) - 1));
}
else
{
__mpz_struct * mpz_ptr = _fmpz_promote(f);
flint_mpz_set_ui(mpz_ptr, 1);
mpz_mul_2exp(mpz_ptr, mpz_ptr, exp);
flint_mpz_sub_ui(mpz_ptr, mpz_ptr, -d);
}
}
}
else /*g is large */
{
__mpz_struct * mpz_ptr = _fmpz_promote(f); /* g is already large */
mpz_fdiv_r_2exp(mpz_ptr, COEFF_TO_PTR(d), exp);
_fmpz_demote_val(f); /* division may make value small */
}
}