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gcdex.c
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gcdex.c
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/* This file is part of the MAYLIB libray.
Copyright 2007-2018 Patrick Pelissier
This Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.
This 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 Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with th Library; see the file COPYING.LESSER.txt.
If not, write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston,
MA 02110-1301, USA. */
#include "may-impl.h"
static int
HalfExtendedEuclidian2 (may_t *s, may_t *g, may_t a, may_t b, may_t x)
{
may_t a1, b1;
may_mark_t mark;
may_mark (mark);
/* Naive & Slow implementation of the Euclidean algorithm */
a1 = may_set_ui (1);
b1 = may_set_ui (0);
while (!may_zero_p (b)) {
may_t q, r;
int i = may_div_qr (&q, &r, a, b, x);
if (i == 0)
return 0;
a = b;
b = r;
r = may_eval (may_sub_c (a1, may_mul_c (q, b1)));
a1 = b1;
b1 = r;
may_compact_va (mark, &a, &b, &a1, &b1, NULL);
}
*s = a1;
*g = a;
return 1;
}
int
may_gcdex (may_t *s_p, may_t *t_p, may_t *g_p,
may_t a, may_t b, may_t c, may_t x)
{
may_t s, t, g, q, r;
int i;
may_mark_t mark;
may_mark (mark);
s = t = g = 0;
/* Compute (s, g) */
i = HalfExtendedEuclidian2 (&s, &g, a, b, x);
if (i == 0)
return may_keep (mark, NULL), 0;
/* Find the solution for c if requested */