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

86 lines
2.4 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) 2009 William Hart
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "ulong_extras.h"
#include "fmpz.h"
ulong
z_gcd(slong a, slong b)
{
ulong ua = FLINT_ABS(a);
ulong ub = FLINT_ABS(b);
return n_gcd_full(ua, ub);
}
void
fmpz_gcd(fmpz_t f, const fmpz_t g, const fmpz_t h)
{
fmpz c1 = *g;
fmpz c2 = *h;
if (fmpz_is_zero(g))
{
fmpz_abs(f, h);
return;
}
if (fmpz_is_zero(h))
{
fmpz_abs(f, g);
return;
}
if (!COEFF_IS_MPZ(c1)) /* g is small */
{
if (!COEFF_IS_MPZ(c2)) /* h is also small */
{
fmpz_set_si(f, z_gcd(c1, c2));
}
else /* h is large, but g is small */
{
fmpz c2d = fmpz_fdiv_ui(h, FLINT_ABS(c1));
fmpz_set_si(f, z_gcd(c1, c2d));
}
}
else
{
if (!COEFF_IS_MPZ(c2)) /* h is small, but g is large */
{
fmpz c1d = fmpz_fdiv_ui(g, FLINT_ABS(c2));
fmpz_set_si(f, z_gcd(c2, c1d));
}
else /* g and h are both large */
{
__mpz_struct *mpz_ptr = _fmpz_promote(f); /* aliasing fine as g, h already large */
mpz_gcd(mpz_ptr, COEFF_TO_PTR(c1), COEFF_TO_PTR(c2));
_fmpz_demote_val(f); /* gcd may be small */
}
}
}