void
nmod_poly_xgcd_hgcd(nmod_poly_t G, nmod_poly_t S, nmod_poly_t T,
const nmod_poly_t A, const nmod_poly_t B)
{
if (A->length < B->length)
{
nmod_poly_xgcd_hgcd(G, T, S, B, A);
}
else /* lenA >= lenB >= 0 */
{
const slong lenA = A->length, lenB = B->length;
mp_limb_t inv;
if (lenA == 0) /* lenA = lenB = 0 */
{
nmod_poly_zero(G);
nmod_poly_zero(S);
nmod_poly_zero(T);
}
else if (lenB == 0) /* lenA > lenB = 0 */
{
inv = n_invmod(A->coeffs[lenA - 1], A->mod.n);
nmod_poly_scalar_mul_nmod(G, A, inv);
nmod_poly_zero(T);
nmod_poly_set_coeff_ui(S, 0, inv);
S->length = 1;
}
else if (lenB == 1) /* lenA >= lenB = 1 */
{
nmod_poly_fit_length(T, 1);
T->length = 1;
T->coeffs[0] = n_invmod(B->coeffs[0], A->mod.n);
nmod_poly_one(G);
nmod_poly_zero(S);
}
else /* lenA >= lenB >= 2 */
{
mp_ptr g, s, t;
slong lenG;
if (G == A || G == B)
{
g = _nmod_vec_init(FLINT_MIN(lenA, lenB));
}
else
{
nmod_poly_fit_length(G, FLINT_MIN(lenA, lenB));
g = G->coeffs;
}
if (S == A || S == B)
{
s = _nmod_vec_init(FLINT_MAX(lenB - 1, 2));
}
else
{
nmod_poly_fit_length(S, FLINT_MAX(lenB - 1, 2));
s = S->coeffs;
}
if (T == A || T == B)
{
t = _nmod_vec_init(FLINT_MAX(lenA - 1, 2));
}
else
{
nmod_poly_fit_length(T, FLINT_MAX(lenA - 1, 2));
t = T->coeffs;
}
if (lenA >= lenB)
lenG = _nmod_poly_xgcd_hgcd(g, s, t, A->coeffs, lenA,
B->coeffs, lenB, A->mod);
else
lenG = _nmod_poly_xgcd_hgcd(g, t, s, B->coeffs, lenB,
A->coeffs, lenA, A->mod);
if (G == A || G == B)
{
flint_free(G->coeffs);
G->coeffs = g;
G->alloc = FLINT_MIN(lenA, lenB);
}
if (S == A || S == B)
{
flint_free(S->coeffs);
S->coeffs = s;
S->alloc = FLINT_MAX(lenB - 1, 2);
}
if (T == A || T == B)
{
flint_free(T->coeffs);
T->coeffs = t;
T->alloc = FLINT_MAX(lenA - 1, 2);
}
G->length = lenG;
S->length = FLINT_MAX(lenB - lenG, 1);
T->length = FLINT_MAX(lenA - lenG, 1);
MPN_NORM(S->coeffs, S->length);
MPN_NORM(T->coeffs, T->length);
if (G->coeffs[lenG - 1] != 1)
{
inv = n_invmod(G->coeffs[lenG - 1], A->mod.n);
nmod_poly_scalar_mul_nmod(G, G, inv);
nmod_poly_scalar_mul_nmod(S, S, inv);
nmod_poly_scalar_mul_nmod(T, T, inv);
}
}
}
}
int
main(void)
{
int i, result;
flint_rand_t state;
flint_randinit(state);
printf("xgcd_hgcd....");
fflush(stdout);
/*
Compare with result from gcd and check a*s + b*t = g
*/
for (i = 0; i < 1000; i++)
{
nmod_poly_t a, b, c, g1, g2, s, t, sum, temp;
mp_limb_t n;
do n = n_randtest_not_zero(state);
while (!n_is_probabprime(n));
nmod_poly_init(a, n);
nmod_poly_init(b, n);
nmod_poly_init(c, n);
nmod_poly_init(g1, n);
nmod_poly_init(g2, n);
nmod_poly_init(s, n);
nmod_poly_init(t, n);
nmod_poly_init(sum, n);
nmod_poly_init(temp, n);
nmod_poly_randtest(a, state, n_randint(state, 600));
nmod_poly_randtest(b, state, n_randint(state, 600));
nmod_poly_randtest(c, state, n_randint(state, 400));
nmod_poly_mul(a, a, c);
nmod_poly_mul(b, b, c);
nmod_poly_gcd(g1, a, b);
nmod_poly_xgcd_hgcd(g2, s, t, a, b);
nmod_poly_mul(sum, s, a);
nmod_poly_mul(temp, t, b);
nmod_poly_add(sum, sum, temp);
result = (nmod_poly_equal(g1, g2) && nmod_poly_equal(g1, sum)
&& (g1->length == 0 || g1->coeffs[g1->length - 1] == 1));
if (!result)
{
printf("FAIL:\n");
nmod_poly_print(a), printf("\n\n");
nmod_poly_print(b), printf("\n\n");
nmod_poly_print(c), printf("\n\n");
nmod_poly_print(g1), printf("\n\n");
nmod_poly_print(g2), printf("\n\n");
nmod_poly_print(sum), printf("\n\n");
nmod_poly_print(s), printf("\n\n");
nmod_poly_print(t), printf("\n\n");
printf("n = %ld\n", n);
abort();
}
nmod_poly_clear(a);
nmod_poly_clear(b);
nmod_poly_clear(c);
nmod_poly_clear(g1);
nmod_poly_clear(g2);
nmod_poly_clear(s);
nmod_poly_clear(t);
nmod_poly_clear(sum);
nmod_poly_clear(temp);
}
/* Check aliasing of a and g */
for (i = 0; i < 200; i++)
{
nmod_poly_t a, b, g, s, t;
mp_limb_t n;
do n = n_randtest(state);
while (!n_is_probabprime(n));
nmod_poly_init(a, n);
nmod_poly_init(b, n);
nmod_poly_init(g, n);
nmod_poly_init(s, n);
nmod_poly_init(t, n);
nmod_poly_randtest(a, state, n_randint(state, 200));
nmod_poly_randtest(b, state, n_randint(state, 200));
nmod_poly_xgcd_hgcd(g, s, t, a, b);
nmod_poly_xgcd_hgcd(a, s, t, a, b);
result = (nmod_poly_equal(a, g));
if (!result)
{
printf("FAIL:\n");
nmod_poly_print(a), printf("\n\n");
nmod_poly_print(b), printf("\n\n");
nmod_poly_print(g), printf("\n\n");
printf("n = %ld\n", n);
abort();
}
nmod_poly_clear(a);
nmod_poly_clear(b);
nmod_poly_clear(g);
nmod_poly_clear(s);
nmod_poly_clear(t);
}
/* Check aliasing of b and g */
for (i = 0; i < 200; i++)
{
nmod_poly_t a, b, g, s, t;
mp_limb_t n;
do n = n_randtest(state);
while (!n_is_probabprime(n));
nmod_poly_init(a, n);
nmod_poly_init(b, n);
nmod_poly_init(g, n);
nmod_poly_init(s, n);
nmod_poly_init(t, n);
nmod_poly_randtest(a, state, n_randint(state, 200));
nmod_poly_randtest(b, state, n_randint(state, 200));
nmod_poly_xgcd_hgcd(g, s, t, a, b);
nmod_poly_xgcd_hgcd(b, s, t, a, b);
result = (nmod_poly_equal(b, g));
if (!result)
{
printf("FAIL:\n");
nmod_poly_print(a), printf("\n\n");
nmod_poly_print(b), printf("\n\n");
nmod_poly_print(g), printf("\n\n");
printf("n = %ld\n", n);
abort();
}
nmod_poly_clear(a);
nmod_poly_clear(b);
nmod_poly_clear(g);
nmod_poly_clear(s);
nmod_poly_clear(t);
}
/* Check aliasing of s and a */
for (i = 0; i < 200; i++)
{
nmod_poly_t a, b, g, s, t;
mp_limb_t n;
do n = n_randtest(state);
while (!n_is_probabprime(n));
nmod_poly_init(a, n);
nmod_poly_init(b, n);
nmod_poly_init(g, n);
nmod_poly_init(s, n);
nmod_poly_init(t, n);
nmod_poly_randtest(a, state, n_randint(state, 200));
nmod_poly_randtest(b, state, n_randint(state, 200));
nmod_poly_xgcd_hgcd(g, s, t, a, b);
nmod_poly_xgcd_hgcd(g, a, t, a, b);
result = (nmod_poly_equal(s, a));
if (!result)
{
printf("FAIL:\n");
nmod_poly_print(a), printf("\n\n");
nmod_poly_print(s), printf("\n\n");
printf("n = %ld\n", n);
abort();
}
nmod_poly_clear(a);
nmod_poly_clear(b);
nmod_poly_clear(g);
nmod_poly_clear(s);
nmod_poly_clear(t);
}
/* Check aliasing of s and b */
for (i = 0; i < 200; i++)
{
nmod_poly_t a, b, g, s, t;
mp_limb_t n;
do n = n_randtest(state);
while (!n_is_probabprime(n));
nmod_poly_init(a, n);
nmod_poly_init(b, n);
nmod_poly_init(g, n);
nmod_poly_init(s, n);
nmod_poly_init(t, n);
nmod_poly_randtest(a, state, n_randint(state, 200));
nmod_poly_randtest(b, state, n_randint(state, 200));
nmod_poly_xgcd_hgcd(g, s, t, a, b);
nmod_poly_xgcd_hgcd(g, b, t, a, b);
result = (nmod_poly_equal(s, b));
if (!result)
{
printf("FAIL:\n");
nmod_poly_print(b), printf("\n\n");
nmod_poly_print(s), printf("\n\n");
printf("n = %ld\n", n);
abort();
}
nmod_poly_clear(a);
nmod_poly_clear(b);
nmod_poly_clear(g);
nmod_poly_clear(s);
nmod_poly_clear(t);
}
/* Check aliasing of t and a */
for (i = 0; i < 200; i++)
{
nmod_poly_t a, b, g, s, t;
mp_limb_t n;
do n = n_randtest(state);
while (!n_is_probabprime(n));
nmod_poly_init(a, n);
nmod_poly_init(b, n);
nmod_poly_init(g, n);
nmod_poly_init(s, n);
nmod_poly_init(t, n);
nmod_poly_randtest(a, state, n_randint(state, 200));
nmod_poly_randtest(b, state, n_randint(state, 200));
nmod_poly_xgcd_hgcd(g, s, t, a, b);
nmod_poly_xgcd_hgcd(g, s, a, a, b);
result = (nmod_poly_equal(t, a));
if (!result)
{
printf("FAIL:\n");
nmod_poly_print(a), printf("\n\n");
nmod_poly_print(t), printf("\n\n");
printf("n = %ld\n", n);
abort();
}
nmod_poly_clear(a);
nmod_poly_clear(b);
nmod_poly_clear(g);
nmod_poly_clear(s);
nmod_poly_clear(t);
}
/* Check aliasing of t and b */
for (i = 0; i < 200; i++)
{
nmod_poly_t a, b, g, s, t;
mp_limb_t n;
do n = n_randtest(state);
while (!n_is_probabprime(n));
nmod_poly_init(a, n);
nmod_poly_init(b, n);
nmod_poly_init(g, n);
nmod_poly_init(s, n);
nmod_poly_init(t, n);
nmod_poly_randtest(a, state, n_randint(state, 200));
nmod_poly_randtest(b, state, n_randint(state, 200));
nmod_poly_xgcd_hgcd(g, s, t, a, b);
nmod_poly_xgcd_hgcd(g, s, b, a, b);
result = (nmod_poly_equal(t, b));
if (!result)
{
printf("FAIL:\n");
nmod_poly_print(b), printf("\n\n");
nmod_poly_print(t), printf("\n\n");
printf("n = %ld\n", n);
abort();
}
nmod_poly_clear(a);
nmod_poly_clear(b);
nmod_poly_clear(g);
nmod_poly_clear(s);
nmod_poly_clear(t);
}
flint_randclear(state);
printf("PASS\n");
return 0;
}
