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

108 lines
3.5 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 <stdio.h>
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "ulong_extras.h"
#include "fmpz.h"
void
fmpz_fdiv_qr(fmpz_t f, fmpz_t s, const fmpz_t g, const fmpz_t h)
{
fmpz c1 = *g;
fmpz c2 = *h;
if (fmpz_is_zero(h))
{
flint_printf("Exception (fmpz_fdiv_q). Division by zero.\n");
abort();
}
if (!COEFF_IS_MPZ(c1)) /* g is small */
{
if (!COEFF_IS_MPZ(c2)) /* h is also small */
{
fmpz q = c1 / c2; /* compute C quotient */
fmpz r = c1 - c2 * q; /* compute remainder */
if ((c2 > WORD(0) && r < WORD(0)) || (c2 < WORD(0) && r > WORD(0)))
{
q--; /* q cannot overflow as remainder implies |c2| != 1 */
r += c2;
}
fmpz_set_si(f, q);
fmpz_set_si(s, r);
}
else /* h is large and g is small */
{
if (c1 == WORD(0))
{
fmpz_set_ui(f, WORD(0)); /* g is zero */
fmpz_set_si(s, c1);
}
else if ((c1 < WORD(0) && fmpz_sgn(h) < 0) || (c1 > WORD(0) && fmpz_sgn(h) > 0)) /* signs are the same */
{
fmpz_zero(f); /* quotient is positive, round down to zero */
fmpz_set_si(s, c1);
}
else
{
fmpz_add(s, g, h);
fmpz_set_si(f, WORD(-1)); /* quotient is negative, round down to minus one */
}
}
}
else /* g is large */
{
__mpz_struct *mpz_ptr, *mpz_ptr2;
_fmpz_promote(f); /* must not hang on to ptr whilst promoting s */
mpz_ptr2 = _fmpz_promote(s);
mpz_ptr = COEFF_TO_PTR(*f);
if (!COEFF_IS_MPZ(c2)) /* h is small */
{
if (c2 > 0) /* h > 0 */
{
flint_mpz_fdiv_qr_ui(mpz_ptr, mpz_ptr2, COEFF_TO_PTR(c1), c2);
}
else
{
flint_mpz_cdiv_qr_ui(mpz_ptr, mpz_ptr2, COEFF_TO_PTR(c1), -c2);
mpz_neg(mpz_ptr, mpz_ptr);
}
}
else /* both are large */
{
mpz_fdiv_qr(mpz_ptr, mpz_ptr2, COEFF_TO_PTR(c1), COEFF_TO_PTR(c2));
}
_fmpz_demote_val(f); /* division by h may result in small value */
_fmpz_demote_val(s); /* division by h may result in small value */
}
}