void
fmpq_poly_revert_series_lagrange_fast(fmpq_poly_t res,
const fmpq_poly_t poly, slong n)
{
fmpz *copy;
int alloc;
if (poly->length < 2 || !fmpz_is_zero(poly->coeffs)
|| fmpz_is_zero(poly->coeffs + 1))
{
flint_printf("Exception (fmpq_poly_revert_series_lagrange_fast). Input must \n"
"have zero constant term and nonzero coefficient of x^1.\n");
abort();
}
if (n < 2)
{
fmpq_poly_zero(res);
return;
}
if (poly->length >= n)
{
copy = poly->coeffs;
alloc = 0;
}
else
{
slong i;
copy = (fmpz *) flint_malloc(n * sizeof(fmpz));
for (i = 0; i < poly->length; i++)
copy[i] = poly->coeffs[i];
for ( ; i < n; i++)
copy[i] = 0;
alloc = 1;
}
if (res != poly)
{
fmpq_poly_fit_length(res, n);
_fmpq_poly_revert_series_lagrange_fast(res->coeffs,
res->den, copy, poly->den, n);
}
else
{
fmpq_poly_t t;
fmpq_poly_init2(t, n);
_fmpq_poly_revert_series_lagrange_fast(t->coeffs,
t->den, copy, poly->den, n);
fmpq_poly_swap(res, t);
fmpq_poly_clear(t);
}
_fmpq_poly_set_length(res, n);
_fmpq_poly_normalise(res);
if (alloc)
flint_free(copy);
}
void
_fmpq_poly_revert_series(fmpz * Qinv, fmpz_t den,
const fmpz * Q, const fmpz_t Qden, long n)
{
_fmpq_poly_revert_series_lagrange_fast(Qinv, den, Q, Qden, n);
}
