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

83 lines
2.6 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"
void
fmpz_mod(fmpz_t f, const fmpz_t g, const fmpz_t h)
{
fmpz c1 = *g;
fmpz c2 = *h;
if (!COEFF_IS_MPZ(c1)) /* g is small */
{
if (!COEFF_IS_MPZ(c2)) /* h is also small */
{
slong r;
if (c2 < WORD(0))
c2 = -c2;
if (c1 < WORD(0))
{
r = c2 - (-c1 % c2); /* C doesn't correctly handle negative mods */
if (r == c2)
r = 0;
}
else
r = c1 % c2;
fmpz_set_si(f, r);
}
else /* h is large and g is small */
{
if (c1 < WORD(0))
{
fmpz_abs(f, h);
fmpz_sub_ui(f, f, -c1);
}
else
fmpz_set_ui(f, c1);
}
}
else /* g is large */
{
if (!COEFF_IS_MPZ(c2)) /* h is small */
{
if (c2 < WORD(0))
fmpz_set_si(f, flint_mpz_fdiv_ui(COEFF_TO_PTR(c1), -c2));
else
fmpz_set_ui(f, flint_mpz_fdiv_ui(COEFF_TO_PTR(c1), c2));
}
else /* both are large */
{
__mpz_struct *mpz_ptr = _fmpz_promote(f);
mpz_mod(mpz_ptr, COEFF_TO_PTR(c1), COEFF_TO_PTR(c2));
_fmpz_demote_val(f); /* reduction mod h may result in small value */
}
}
}