freebsd-dev/contrib/libgmp/mpz/gcdext.c

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/* mpz_gcdext(g, s, t, a, b) -- Set G to gcd(a, b), and S and T such that
g = as + bt.
Copyright (C) 1991, 1993, 1994, 1995 Free Software Foundation, Inc.
This file is part of the GNU MP Library.
The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
The GNU MP Library 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 Library General Public
License for more details.
You should have received a copy of the GNU Library General Public License
along with the GNU MP Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "gmp-impl.h"
/* Botch: SLOW! */
void
#if __STDC__
mpz_gcdext (mpz_ptr g, mpz_ptr s, mpz_ptr t, mpz_srcptr a, mpz_srcptr b)
#else
mpz_gcdext (g, s, t, a, b)
mpz_ptr g;
mpz_ptr s;
mpz_ptr t;
mpz_srcptr a;
mpz_srcptr b;
#endif
{
mpz_t s0, s1, q, r, x, d0, d1;
mpz_init_set_ui (s0, 1L);
mpz_init_set_ui (s1, 0L);
mpz_init (q);
mpz_init (r);
mpz_init (x);
mpz_init_set (d0, a);
mpz_init_set (d1, b);
while (d1->_mp_size != 0)
{
mpz_tdiv_qr (q, r, d0, d1);
mpz_set (d0, d1);
mpz_set (d1, r);
mpz_mul (x, s1, q);
mpz_sub (x, s0, x);
mpz_set (s0, s1);
mpz_set (s1, x);
}
if (t != NULL)
{
mpz_mul (x, s0, a);
mpz_sub (x, d0, x);
if (b->_mp_size == 0)
t->_mp_size = 0;
else
mpz_tdiv_q (t, x, b);
}
mpz_set (s, s0);
mpz_set (g, d0);
if (g->_mp_size < 0)
{
g->_mp_size = -g->_mp_size;
s->_mp_size = -s->_mp_size;
if (t != NULL)
t->_mp_size = -t->_mp_size;
}
mpz_clear (s0);
mpz_clear (s1);
mpz_clear (q);
mpz_clear (r);
mpz_clear (x);
mpz_clear (d0);
mpz_clear (d1);
}