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/*
Copyright (C) 2009 William Hart
This file is part of FLINT.
FLINT is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License (LGPL) as published
by the Free Software Foundation; either version 3 of the License, or
(at your option) any later version. See <https://www.gnu.org/licenses/>.
*/
#include "test_helpers.h"
#include "ulong_extras.h"
TEST_FUNCTION_START(n_gcdinv, state)
{
slong ix;
int result;
/* test modulo 1 */
{
ulong a, b, s, g;
a = 0;
b = 1;
g = n_gcdinv(&s, a, b);
result = (g == 1 && s == 0);
if (!result)
TEST_FUNCTION_FAIL(
"GCD modulo 1 does not return g = 1 and s = 0\n"
"g = %wu, s = %wu\n",
g, s);
}
/* check gcd not 1 when a = 0 (and b != 1) */
for (ix = 0; ix < 1000 * flint_test_multiplier(); ix++)
{
ulong a, b, s, g;
a = 0;
b = n_randtest_not_zero(state);
g = n_gcdinv(&s, a, b);
result = (g != 1 || b == 1);
if (!result)
TEST_FUNCTION_FAIL(
"gcd(0, b) == 1\n"
"b = %wu, s = %wu\n",
b, s);
}
for (ix = 0; ix < 10000 * flint_test_multiplier(); ix++)
{
ulong a, b, c, g, g2, s, t2, t, bits1, bits2, bits3, ainv;
bits1 = n_randint(state, FLINT_BITS - 1) + 2;
bits2 = n_randint(state, bits1) + 1;
bits3 =
bits1 == FLINT_BITS ? 0 : n_randint(state, FLINT_BITS - bits1) + 1;
do
{
a = n_randtest_bits(state, bits1);
b = n_randtest_bits(state, bits2);
} while (n_gcd(a, b) != UWORD(1) || b >= a);
c = bits3 == 0 ? 1 : n_randtest_bits(state, bits3);
/* compare n_gcdinv with n_xgcd */
g = n_xgcd(&s, &t, a * c, b * c);
g2 = n_gcdinv(&t2, b * c, a * c);
/* compute second cofactor modulo ac */
t %= (a * c); /* t is non-negative... */
t = a * c - t; /* ... but minus the actual cofactor */
result = (g == g2 && t == t2);
if (!result)
TEST_FUNCTION_FAIL(
"Cofactor doesn't agree with n_xgcd\n"
"a = %wu, b = %wu, c = %wu\n"
"g = %wu, g2 = %wu, t = %wd, t2 = %wd\n",
a, b, c, g, g2, t, t2);
/* test b*t2 == 1 mod a */
ainv = n_preinvert_limb(a);
s = n_mulmod2_preinv(t2, b, a, ainv);
result = (s == 1);
if (!result)
TEST_FUNCTION_FAIL(
"Incorrect inverse\n"
"a = %wu, b = %wu, c = %wu\n"
"g2 = %wu, s = %wd, t2 = %wd\n",
a, b, c, g2, s, t2);
}
TEST_FUNCTION_END(state);
}