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/*
Copyright (C) 2021 Fredrik Johansson
This file is part of Arb.
Arb 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 2.1 of the License, or
(at your option) any later version. See <http://www.gnu.org/licenses/>.
*/
#include "acb_hypgeom.h"
static void
bsplit(acb_ptr res, const acb_t x, ulong a, ulong b, slong trunc, slong prec)
{
trunc = FLINT_MIN(trunc, b - a + 1);
if (b - a <= 12)
{
if (a == 0)
{
acb_hypgeom_rising_ui_jet_powsum(res, x, b - a, FLINT_MIN(trunc, b - a + 1), prec);
}
else
{
acb_t t;
acb_init(t);
acb_add_ui(t, x, a, prec);
acb_hypgeom_rising_ui_jet_powsum(res, t, b - a, FLINT_MIN(trunc, b - a + 1), prec);
acb_clear(t);
}
}
else
{
acb_ptr L, R;
slong len1, len2;
slong m = a + (b - a) / 2;
len1 = poly_pow_length(2, m - a, trunc);
len2 = poly_pow_length(2, b - m, trunc);
L = _acb_vec_init(len1 + len2);
R = L + len1;
bsplit(L, x, a, m, trunc, prec);
bsplit(R, x, m, b, trunc, prec);
_acb_poly_mullow(res, L, len1, R, len2,
FLINT_MIN(trunc, len1 + len2 - 1), prec);
_acb_vec_clear(L, len1 + len2);
}
}
void
acb_hypgeom_rising_ui_jet_bs(acb_ptr res, const acb_t x, ulong n, slong len, slong prec)
{
if (len == 0)
return;
if (len > n + 1)
{
_acb_vec_zero(res + n + 1, len - n - 1);
len = n + 1;
}
if (len == n + 1)
{
acb_one(res + n);
len = n;
}
if (n <= 1)
{
if (n == 1)
acb_set_round(res, x, prec);
return;
}
bsplit(res, x, 0, n, len, prec);
}
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