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/*=============================================================================
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) 2012 William Hart
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "ulong_extras.h"
#include "fmpz.h"
void
fmpz_xgcd(fmpz_t d, fmpz_t a, fmpz_t b, const fmpz_t f, const fmpz_t g)
{
fmpz_t t1, t2;
fmpz *f1, *g1;
if (fmpz_is_zero(f))
{
int sign = fmpz_sgn(g);
fmpz_abs(d, g);
fmpz_set_ui(a, 0);
if (sign == 0)
fmpz_set_ui(b, 0);
else if (sign > 0)
fmpz_set_ui(b, 1);
else
fmpz_set_si(b, -1);
}
else if (fmpz_cmp(f, g) == 0)
{
if (fmpz_sgn(f) > 0)
{
fmpz_set(d, f);
fmpz_set_ui(a, 1);
}
else
{
fmpz_neg(d, f);
fmpz_set_si(a, -1);
}
fmpz_set_si(b, 0);
}
else
{
int sign1 = fmpz_sgn(f);
int sign2 = fmpz_sgn(g);
fmpz_init(t1);
fmpz_init(t2);
/* support aliasing */
if (d == f || a == f || sign1 < 0)
{
f1 = t1;
if (sign1 < 0)
fmpz_neg(f1, f);
else
fmpz_set(f1, f);
}
else
f1 = (fmpz *) f;
if (d == g || a == g || sign2 < 0)
{
g1 = t2;
if (sign2 < 0)
fmpz_neg(g1, g);
else
fmpz_set(g1, g);
}
else
g1 = (fmpz *) g;
if (fmpz_cmp(f1, g1) < 0)
{
fmpz_gcdinv(d, a, f1, g1);
fmpz_mul(t1, a, f1);
fmpz_sub(t1, d, t1);
fmpz_divexact(b, t1, g1);
}
else /* g < f */
{
fmpz_gcdinv(d, b, g1, f1);
fmpz_mul(t2, b, g1);
fmpz_sub(t2, d, t2);
fmpz_divexact(a, t2, f1);
}
if (sign1 < 0)
fmpz_neg(a, a);
if (sign2 < 0)
fmpz_neg(b, b);
fmpz_clear(t1);
fmpz_clear(t2);
}
}
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