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

61 lines
2.1 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_sub_ui(fmpz_t f, const fmpz_t g, ulong x)
{
fmpz c = *g;
if (!COEFF_IS_MPZ(c)) /* coeff is small */
{
mp_limb_t sum[2];
if (c < WORD(0)) /* g negative, x positive, so difference is negative */
{
add_ssaaaa(sum[1], sum[0], 0, -c, 0, x);
fmpz_neg_uiui(f, sum[1], sum[0]);
}
else /* coeff is non-negative, x non-negative */
{
if (x < c)
fmpz_set_ui(f, c - x); /* won't be negative and is smaller than c */
else
fmpz_neg_ui(f, x - c); /* positive or zero */
}
}
else
{
__mpz_struct *mpz_ptr, *mpz_ptr2;
mpz_ptr2 = _fmpz_promote(f); /* g is already large */
mpz_ptr = COEFF_TO_PTR(c);
flint_mpz_sub_ui(mpz_ptr2, mpz_ptr, x);
_fmpz_demote_val(f); /* cancellation may have occurred */
}
}